International Workshop on Radiation Imaging Detectors iWoRID 2011

3 Jul 2011, 15:30 → 7 Jul 2011, 18:00 Europe/Zurich

HG E7 (ETH Zurich, Switzerland)

Bernd Schmitt (Head of SLS Detector Group)

© Zurich Tourismus

The International Workshop on Radiation Imaging Detectors is held yearly and provides an international forum for discussing current research and developments in the area of position sensitive detectors for radiation imaging, including semiconductor detectors, gas- and scintillator-based detectors. Topics include processing and characterization of detector materials, design of photon counting or charge integrating electronics, hybridization and interconnect technologies, readout systems and application in various scientific and industrial fields.

Sponsors:

1rst Announcment iworid13_announcement.pdf

Flyer IWoRID_2011_flyer.pdf

Poster IWoRID_2011_Poster.pdf

Sunday, 3 July

17:00 Registration and reception

Alumni Pavillon (former GEP-Pavillon). It is located left from the entrance to Polybahn.

Monday, 4 July

08:00 Registration

Get all the documentation, batches, vouchers etc.

Opening

Convener: Prof. Christer Frojdh (Mid-Sweden University)

1 Opening & Welcome

Speaker: Johannes Friso van der Veen (Paul Scherrer Institut)

2 Honorary Speaker: The History of Silicon Detectors in Particle and X-ray Physics

The talk presents the historical development of silicon detectors. Emphasis is put on the different sensor concepts which have been realized, the performances achieved and selected results from experiments in particle and X-ray science which became possible thanks to silicon detectors.

Speaker: Prof. Robert Klanner

Slides 01_IWORID-RK-110704.pdf

3 Protein Crystallography, present and future detector requirements

Protein crystallography (PX) is particularly demanding of detector performance and historically it has always been the detector that has been the limiting factor in the majority, if not all, diffraction experiments. Ultimately this is due to the need to obtain data with an excellent signal to noise ratio from samples that are limited in size, inherently weakly diffracting and highly susceptible to radiation damage. The requirements of an “ideal” detector for PX will be presented, and the performance of current commercially available detectors will be assessed in the light of these requirements. From this assessment it becomes clear that hybrid pixel detectors satisfy most of the requirements for many experiments, and very fast readout CCDs are also very promising. The remaining shortcomings will be discussed, together with the special requirements of more novel PX experiments.

Speaker: Dr Andrew Leslie (MRC Laboratory of Molecular Biology (LMB) , Cambridge UK)

Minutes Abstract.docx

Slides Detectors_Zurich_Leslie.pptx

10:05 Coffee Break

Sensor Materials, Device Processing & Technologies I: 4 contributions

Convener: Dr Cinzia Da Via (The University of Manchester)

4 State of the art neutron detection, 3He problem and solutions

Over the last years 3He has been widely used in gas filled detectors for neutron scattering due to its outstanding characteristics. Driven by the escalating supply shortage of 3He an International Detector Initiative to develop alternative technologies to 3He detectors for neutron scattering applications was initiated by the major neutron facilities worldwide. Focused on the development of large area detectors the Initiative pursues three potential technologies: - ZnS:6LiF(Ag) or ZnS:10B2O3(Ag) scintillator based detectors read out by coded arrays of clear or wavelength shifting fibres and PMTs recently have been built at several facilities. To substitute 3He-detectors however, these devices need considerable improvement with respect to efficiency, count rate capability, ghosting and production cost. - Gaseous detectors with solid 10Boron converter are presently used in very low efficiency or small area applications only. The deposition of uniform ~1µm thin 10Boron layers on very large areas at reasonable cost and the detector design of multilayer arrangements using up to 30 Boron layers to achieve adequate efficiency is a considerable challenge to apply this technology for neutron scattering applications. - Widely used in the past 10BF3 was abandoned as detector gas due to its intrinsically lower efficiency and toxicity. Improved multilayer detector designs and the availability of high purity gas nowadays are considered as a potential replacement of 3He detectors on a short term. Details of the three different development lines pursued by the International Detector Initiative and present results will be reported.

Speaker: Dr Karl Zeitelhack (TU München, Forschungs-Neutronenquelle Heinz Maier-Leibnitz)

Slides ICNDD-IWORID-2011.ppt

5 Edgeless planar semiconductor sensors for a Medipix3-based digital radiography detector

Due to its advanced pixel circuitry, the Medipix3 chip is an interesting read-out alternative to today’s CCD- and TFT-based digital radiography detectors. Hybridised to a mono-crystalline high-Z semiconductor sensor, it can provide electronic-noise free and fine-grained colour X-ray images of high contrast. Nevertheless, the limited active area of the Medipix3 chip as well as single-crystal sensor wafers currently prevents replacement of large-area X-ray imaging systems. A seamless tessellation of multiple detector modules with edgeless sensors could solve this. We therefore study phenomena affecting the charge collection at the edge of slim-edge and active-edge planar sensors. Two 150 µm thick active-edge n-in-n planar silicon sensors, hybridised to Timepix read-out chips, were mounted side-by-side and placed longitudinally in the CERN-SPS H6 beamline. Consequently, 120 GeV/c muons and pions traversed both sensors practically parallel to chip’s plane and left behind long trails for accurate track reconstruction. The response of the edge pixels to particles traversing the detector under a small inclination and azimuthal angle was studied with two main objectives in mind: (i) to determine the minimum distance from the physical edge at which charge is collected; (ii) to map the electric-field distribution at the edge by relating the Time-over-Threshold information to the reconstructed interaction depth. Additionally, we investigate the potential of reducing the electric field distortion at the edge by seamlessly mounting multiple pieces of slim-edge cadmium telluride on one Medipix chip. Supported by TCAD simulations, the flood-field uniformity of the adjacent edges is compared with that of the perimeter.

Speaker: Mr Marten Bosma (Nikhef)

Slides 02_BOSMA_IWORID13.pptx

6 Recent Results of VTT's Edgeless Detector Prototypes

During past five years VTT has actively developed edgeless detector fabrication process. Our straightforward and high yield process relies on ion-implantation to active the edges of the detector. The presentation covers latest edgeless pixel detector prototype results from CERN’s SPS beam test and X-ray response characterization. In these evaluations 150 um thick n-on-n edgeless detectors have been flip-chip bonded to Medipix2 and Timepix readouts. The focus of the characterization has been in evaluation of the edge response. The results demonstrate that VTT’s edgeless pixel detectors can reliable construct X-ray images and track minimum ionizing particles without information loss at the edge regions. These detectors are suitable for seamless tiling to construct a large area imaging detector. During 2010, latest fabrication process was performed for p-on-n edgeless detectors. The layout contained DC- and AC-coupled strip detectors and pixel detectors for Medipix/Timepix readouts. The fabricated detector thicknesses were 50, 100 and 150 um. The presentation covers electrical characterization results of the edgeless diodes, comprising leakage current, capacitance and breakdown voltage measurements. The results are compared with TCAD simulations of the diode structures to understand the found thickness dependences of the electrical properties.

Speaker: Xiaopeng Wu (VTT)

Slides Recent_Results_of_VTT's_Edgeless_Detector_iWoRID2011.pdf

7 Slim edges in double-sided silicon 3D detectors

Owing to several advantages provided by their peculiar structure, where the electrode distance is decoupled from the active thickness, silicon 3D detectors are emerging as one of the most promising technologies for future experiments at high luminosity particle colliders. An additional feature available with the original 3D technology is the active edge, enabling to reduce the insensitive edge region to less than 10 μm [1]. These interesting properties come at the expense of a rather complicated technology, involving several non standard steps such as wafer bonding and Deep Re-active Ion Etching. Since 2004, we have developed modified 3D architectures aimed at a simplification of the manufacturing technology with respect to the original design. In particular, in the past few years, we have thoroughly investigated 3D-DTTC (Double-side, Double-Type-Column) detectors [2], which involve columnar electrodes of both doping types etched from both wafer sides (junction columns from the front side and ohmic columns from the back side), and stopping at a short distance from the opposite surface. A similar approach is pursued by CNM-IMB (Barcelona, Spain) [3]. In 3D-DDTC detectors, the charge collection efficiency and the radiation hardness critically depend on the columnar electrode overlap. In order to rule out the effects of the column depth non uniformities on the detector characteristics, we have developed a modified 3D-DDTC process allowing for passing-through columns [4]. This advanced 3D-DDTC process still does not require a support wafer, thus avoiding the related wafer bonding and final removal. One additional advantage is that the wafer back-side is fully accessible: the detector substrate bias can be provided from the back-side, and dual-readout detector systems can be easily achieved. Two batches of these new detectors have been fabricated and are currently being tested both in laboratory and in beam tests. A few more batches are being fabricated as a pre-production for the ATLAS Insertable B Layer. In this paper, we focus on one additional design option offered by these detectors, the so called “slim edge”. In fact, the considered technology is not suitable for active edges, due to the absence of the support wafers. However, the active area can be terminated by a multiple ohmic column fence aimed at preventing the depletion region spreading from the outermost junction columns to reach the device physical edge. By doing so, no leakage current contribution from the highly damaged cut-line can reach the active area. Slim edge terminations have been designed with the aid of TCAD simulations and experimentally validated, showing that the insensitive region at the sensor edge can be reduced to less than 100 μm. At the conference, the main design and technological issues will be reviewed and selected results from electrical and position resolved laser tests will be presented. References [1] C. Kenney, et al., IEEE Trans. Nucl. Sci., NS-48 (2001) 2405 [2] A. Zoboli, et al., IEEE Trans. Nucl. Sci., NS-55 (2008) 2775 [3] G. Pellegrini, Nucl. Instrum. Methods A, 592 (2008) 38. [4] G. F. Dalla Betta, et al., 2010 IEEE NSS, Conference Record, paper N15-3

Speaker: Mr Marco Povoli (Università di Trento and INFN Trento, Via Sommarive, 14, 38123 Trento, Italy)

Slides iWORID11_Marco_Povoli.pdf

8 Methods for the characterization of the long-term behaviour of X-ray detectors

Computed tomography (CT) is a non-destructive imaging method that is able to visualize the entire test specimen including inner structures. Its image quality depends on the accuracy of the system components, especially the X-ray detector, X-ray source and the manipulation system. Only the knowledge of characteristics of the components and their influence on image quality allows conclusions about the repeatability of the accuracy of the measurement data. This knowledge is used to ensure the stability of a CT-system as an experimental mould and measurement instrument. In this contribution we will present methods for the characterization of the long-term stability of X-ray detectors. These methods are compared upon their usability on photon counting and charge integrating detectors. For integrating industrial detectors, well-known characterization procedures as the ASTM standards already exist. Some of these methods (e.g. dark current behaviour) cannot be applied to photon counting detectors because of the very different working principles of the detectors. For these new detector technologies, new application fields can be made accessible according to lower energies and lower intensities. Therefore using the standardized spectra required by the ASTM standard for industrial X-ray detectors may not be reasonable. Spectra that are relevant for practical applications of the respective detector have to be chosen for characterization measurements. Other characteristics for photon counting detectors i.e. MTF and efficiency are in contrast to the integrating detectors also functions of the threshold level. Additionally, small active areas of the X-ray detectors may require modified test specimens and expirations. Adapted characterization methods of the long-term behaviour of integrating and photon counting X-ray detectors and their comparison will be presented and discussed in terms of their practicability on different types of detectors and significance to image quality.

Speaker: Mr Stefan Reisinger (Fraunhofer Institut)

Slides Methods_for_the_characterization_of_the_long-term_behaviour_of_X-ray_detectors.pdf

Poster MiniTalks I

Convener: Dr Cinzia Da Via (The University of Manchester)

9 Detection of fast neutrons using detectors based on semi-insulating GaAs

Gallium arsenide (GaAs) is III-V semiconductor compound with promising physical properties (wide bang gap, fast reaction rate and good radiation hardness) for fabrication of detectors for various type of ionizing radiation. In this work we focused on detection of fast neutrons. As GaAs does not directly interacts with fast neutrons, the conversion layer has to be applied. Its task lies on the transformation of the energy of fast neutron to charged particle, which is simply detectable. In our experiments, we used HDPE (High Density PolyEthylene) conversion layer, which has relatively high elastic cross section for fast neutrons scattering. Output products of interaction between HDPE and fast neutrons are recoiled protons. The 238-Pu-Be fast neutrons source was used in our experiment. The energy of generated neutrons varied between 0.5 and 12 MeV with maximum about 3 MeV. Fabricated detectors had Ti/Pt/Au square Schottky contact with the area of 2.5 × 2.5 mm2. On the back side, the whole area AuGeNi eutectic ohmic contact was evaporated. The thickness of the base material (semi-insulating GaAs) was 200 um. The connection of four detectors in parallel was tested to get the detection area of 25 mm2. We have investigated the optimal thickness of HDPE conversion layer for fast neutron source used. The spectra of neutrons were measured by detectors covered by HDPE converter of different thicknesses (150 – 1500 um). The fast neutron detection efficiency proved experimentally was compared with results from simulations performed by MCNP and TRIM/SRIM code.

Speaker: Dr Zaťko Bohumír (Institute of Electrical Engineering, Slovak Academy of Sciences, Bratislava)

Slides Iworid-Zatko_ID133.pptx

10 Development of a highly efficient, high resolution X-ray sensor based on self-organizing aluminum oxide

State of the art X-ray imaging sensors comprise a trade-off between the achievable efficiency and the spatial resolution. For instance a scintillator with a high thickness (i. e. high absorption length), yields a high efficiency but suffers from a decrease in spatial resolution due to (optical) light spreading in the scintillation layer. For thinner scintillators the opposing case is observed. In general, an increase in spatial resolution leads to a decrease in efficiency and vice versa. The goal of the Fraunhofer-internal project WISA Honeris, which has launched in March 2009, is to overcome such limitations to provide ‘ready for the market’ X-ray imaging sensors which offer both high efficiency and high spatial resolution. This is achieved by filling structures (hexagonal arranged channels) of porous self-organized aluminium oxide (AlOx) matrices with appropriate scintillator materials. The process of self-organization itself is based on electrochemical oxidation. Due to its channel-like structures which act as light guides, the high spatial resolution is assured almost independently from the scintillator thickness. This permits the fabrication of very thick and therefore highly efficient scintillator matrices without losing spatial resolution. We used Monte-Carlo X-ray simulations to determine the X-ray imaging quality of the AlOx matrices. Important factors which influence the behaviour of the matrices are: filling factor (ratio between channels and ‘closed’ AlOx), channel diameter, aspect ratio, filling method, filling material etc. Therefore we modelled the porous AlOx matrix with the MC X-ray simulation tool ROSI [1] and evaluated its properties in many different ways to investigate: the performance at different acceleration voltages, antialiasing possibilities, crosstalk between channels as a function of acceleration voltage and filling factor, achievable spatial resolution, homogeneity, etc. We present the results of the simulations which incorporate the response of the matrix to be expected and give a comparison of these results with experimental characterisation measurements for both image and fabrication/filling quality and also a comparison with present available scintillator-filled matrices. [1] J. Giersch, A. Weidemann, G. Anton: ROSI - an Object-Oriented and Parallel-Computing Monte Carlo Simulation for X-Ray Imaging. Nuclear Inst. and Methods in Physics Research A, 509:151–156, 2003.

Speaker: Dr Frank Sukowski (Fraunhofer Development Center X-Ray Technology (EZRT))

11 Evaluation of the limited response property in Silicon Photomultiplier with different micro cell size

The SiPM(silicon photomultiplier) consists of several thousand of micro cells which are operated in geiger mode. In this Geiger mode, only one micro cell is fired when several photons are incident on the same micro cell at the same time. Therefore the dynamic range of the SiPM is determined by the total number of micro cells. The output pulse is shown a linear response when small amount of photons are incident on the detector. However the pulse height became saturated as increasing the amount of the light intensity because of the overlapping of incident photons into same micro cell. This non-linearity response is a severe problem when the number of photoelectrons exceeds the total number of micro cells. A commonly used simple exponential model for the evaluation of the number of fired micro cells from the amount of generated photoelectron is described by poisson distribution. The number of photoelectron is a generated photoelectron from incident photons which contribute to the triggering signal that can be calculated by multiplying the number of incident photons and PDE(photo detection efficiency) of the SiPM. In this study different size of the micro cells are considered with different intensity of incident photons. The energy resolution of the SiPM with considerations of the non linear response was calculated [1] and the statistic photon loss can be considered from the simple exponential model. The SiPM test sample is fabricated with <100> oriented 6 um thick epitaxial wafers having 12 Ω·cm at National Nano Fab Center (NNFC) in Korea. The SiPM is designed with 2 mm of width including 4 different sizes of the microcell; 15, 20, 30, 50 um respectively. Incident photons which have a pulse width less than a recovery time of the SiPM are tested to prevent additional triggering of the micro cell after recharging of the micro cell using a picoseconds laser pulse diode with several wavelengths. Reference [1] A. Stoykov et al “On the limited amplitude resolution of multipixel Geiger-mode APDs, “ J. instrum., vol. 2, p. P06005, Jun. 2007

Speaker: Mr Hyoungtaek Kim (Korea Advanced Institute of Science and Technology)

12 Analasis of CMOS APD with Geiger mode

Because of enhancive integration and advantageous characteristic of high speed and low power dissipation, research on CMOS Geiger mode APD is actively conducted. However, APD fabricated through CMOS process demands higher efficiency of fill factor and modification of interfering noise. Therefore, the study is conducted to derive optimum size of CMOS APD by comparison and analysis of characteristics between P+/N structure APD pixel type 0(fill factor 23.23%) and APD pixel type 1(fill factor 17.46%). The shapes of open PDs and pixels of the two CMOS APDs are same as square. However the sizes are different from each other, pixel type 1 is 83.3um x 83.3um, and the other is 67um x 67um. The area of open PDs are set as 40.6um x 40.6um and 28um x 28um for pixel type 0 and pixel type 1 respectively. Main body of CMOS APD consists of arrays of pixel type 1. We tested Dark Current, Photocurrent, Quantum Efficiency, Dead Time, Gain, Dark Count Rate to analyze the characteristics of the CMOS APDs in this research. We also tested and analyzed the Photon Count Measurement of main body of 8 x 1-array-CMOS-APD with Geiger mode through sequential mode. The result of the study will be announced in detail.

Speaker: Mr Hyun Tae Leem (CMOS APD)

Poster iworid2011_Analysis_of_CMOS_APD_with_Geiger_mode_edition4.pptx

Slides Analysis_of_CMOS_APD_with_Geiger_mode._minitalk.pptx

13 Fluence dependent barrier capacitance and compensation effects in neutron irradiated Si pin diodes

The high resistivity particle Si pin-detectors, operating at full depletion regime, are commonly employed for detection of the ionizing radiation. Radiation induced defects acting as carrier trapping, generation and compensation centers affect the operational parameters of diodes by the increase of leakage current, by reduction of charge collection efficiency and signal to noise ratio. Commonly, these characteristics are examined by employing current-voltage (I-V), capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) techniques, etc. However, at high irradiation fluences (>10^14 cm-2), the mentioned techniques are unacceptable, as C-V characteristics are distorted by generation current leading to misinterpretation of doping effects, while DLTS technique is only applicable if trap density is significantly less than that of dopants. Therefore, techniques capable to separate trapping, generation and compensation effects are needed. In this work, a technique, based on analysis of transients of barrier capacitance charging current induced by linearly increasing voltage pulse, is presented. To extract barrier parameters, the transients for reverse and forward biasing are examined. Fluence dependent variations of barrier capacitance, of space charge generation current and doping compensation effects in neutron irradiated diodes are discussed. It has been shown that generation current, caused by radiation induced traps of high density, distorts capacitance measurements in irradiated devices, while there is no sign inversion effect, however, heavily irradiated detectors become fully depleted in equilibrium.

Speaker: Mr Tomas Ceponis (Vinius University, Institute of Applied Research)

Slides Ceponis-poster_minitalk-101.ppt

14 In situ analysis of carrier lifetime and barrier capacitance variations in silicon during 1.5 MeV protons implantation

Ion implantation technology is commonly employed for modification of material properties, device structures, as well as for introducing fast recombination centers in microelectronic, nanoelectronic and optoelectronic devices. Despite beneficial recombination centers, detrimental defects that affect the device operation are introduced during implantation as well. Therefore, it is essential to analyze the characteristics of these defects. Usually, combined analysis of current-voltage (I-V), capacitance-voltage (C-V), deep level transient spectroscopy (DLTS), transient current technique (TCT) characteristics is employed for investigation of radiation induced defects. However, these techniques are applied in the post irradiated state and do not provide direct information of defects creation processes. Therefore, in situ techniques, capable to reveal the peculiarities of defects creation during ion implantation, are desirable. In this work, results of the in situ analysis of recombination lifetime and barrier capacitance variations in Si substrates and pin diodes, respectively, during 1.5 MeV protons implantation are presented. Carrier recombination lifetime has been measured by employing microwave probed photoconductivity method (MW-PCD), while parameters of barrier capacitance changes have been extracted by transient technique of barrier capacitance charging current measurements using linearly increasing voltage pulses. Sub-linear decrease of carrier lifetime as a function of fluence has been revealed and peculiarities of such characteristic are explained in terms of formation of two layered structure within implanted Si material. Barrier capacitance variations in pin diode structures during 1.5 MeV protons implantation are discussed.

Speaker: Mr Tomas Ceponis (Vinius University, Institute of Applied Research)

Slides Ceponis-poster_minitalk-102.ppt

15 Study of monochromatic X-ray’s depth of interaction in pixellated CdTe detector operating in Time-Over Threshold mode.

High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20 um pinhole to measure the depth of interaction dependence of the detector spectral response. The sensor was a 1 mm thick CdTe detector with a pixel pitch of 110 um, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The measurement was arranged with the beam entering the sensor at an angle of ~20 degrees to the surface. The beam then passed through ~25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77 keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-Over-Threshold mode were recorded showing each individual interaction along the beam path. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the top part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field. In addition to the depth of interaction measurement we have performed a general synchrotron characterization of the detector with respect to uniformity, energy resolution and charge sharing effects.

Speaker: Mr Erik Fröjdh (Mid Sweden University)

Slides erikfrojdh_minitalk.pdf

16 Feasibility study of direct-conversion radiation detector using cadmium zinc telluride

The ultimate object of this paper is to develop direct conversion radiation detector based on Cd(Zn)Te. A polycrystalline Cd(Zn)Te film was deposited using vacuum thermal evaporation technique as fundamental study of large area film fabrication and then investigated the effect on radiation detection characteristics through physical and electrical measurement. First, the composition and structural morphology of deposited Cd1-xZnxTe was investigated using EPMA, XRD and SEM. Also, leakage current and sensitivity was measured to study radiation response characteristics. In addition, there was made a comparative study of radiation response characteristics on multilayer Cd(Zn)Te samples formed with dielectric layer and blocking layer. As results, the structure of deposited film was consisted of polycrystalline with Zincblend phase on CdTe and with Cubic zincblend on CdZnTe. The dark current of CdTe samples showed lower value at positive bias than negative bias, and then Cd0.85Zn0.15Te compared to CdTe was lower by a factor ～10. Also, The lower and stable dark current was measured in sample consisted of ITO than Al as bottom electrode and the lowest dark current was obtained in Cd0.85Zn0.15Te sample of MOS structure formed with CeO2 layer. In sensitivity measurement, in Cd0.85Zn0.15Te sample of MOS structure with ITO electrode the highest value was measured as total output charge and SNR were 180.44 pC/cm2(1.1×109 e-/cm2) and 6.19 at 30 V. In Cd1-xZnxTe(x=0.15, 0.25, 0.3) samples, dark current showed the lowest value of Cd0.7Zn0.3Te and output charge relatively showed similar values. These results was seemed due to thickness of Cd(Zn)Te layer. As results, the fabrication condition of Cd(Zn)Te based radiation detector was investigated using vacuum deposition method. In electrical measurement, as Zn composition increased the dark current was reduced due to increased resistivity, and then the Cd(Zn)Te detector of multilayer structure formed with dielectric and blocking layer protected from charge injection showed the feasibility as good radiation conversion layer for flat panel radiation imaging system. But, Increasing Zn composition, net charge reduced due to density reduction. Therefore the optimization of Zn composition in CdTe will be required.

Speaker: Mr kang sang sik (radiological science of korea international university)

17 Overview of 3D- Silicon sensors development for ATLAS Pixel Upgrade

An upgrade of LHC towards a 10 times higher luminosity will require tracking pixel detectors with unprecedented radiation tolerance. Furthermore the high track density will call for fast and high granularity pixel detectors with low radiation length and power consumption. Different types of solid-state sensors are being studied for ATLAS upgrade of tracking system within ATLAS Insertable B-Layer and High Luminosity LHC programs. The Silicon 3D sensors which have been proposed and developed within ATLAS 3D Collaboration are potentially more radiation hard and have a faster charge collection than the standard planar sensor owing to the innovative electrode configuration. These new sensor represent an excellent candidate for the pixel sensor at ATLAS upgrade. In the framework of ATLAS 3D Collaboration different technologies are carried out to obtained Silicon 3D sensors: (i) Full-3d with active edge by Stanford and Sintef and (ii) double side double column type (DDTC) with partial and fully penetrating electrodes in the substrate by FBK-irst and CNM. With these technologies several sensors have been produced and tested with the ATLAS Pixel front-end chips. We will describe recent development in these sensor technologies and will concentrate on recent results obtained with lab- and beam-tested devices --- A. La Rosa (Wisconsin Univ. and CERN) on behalf of ATLAS 3D Collaboration

Speaker: Mr Marcello Borri

18 Simulation and Measurement of Absorbed Dose from 137 Cs gammas using a Si Timepix Detector

The TimePix readout chip is a hybrid pixel detector with over 65k independent pixel elements. Each pixel contains its own circuitry for charge collection, counting logic, and readout. When coupled with a Silicon detector layer, the Timepix chip is capable of measuring the charge, and thus energy, deposited in the Silicon. Measurements using a NIST traceable 137Cs gamma source have been made at Johnson Space Center using such a Si Timepix detector, and this data is compared to simulations of energy deposition in the Si layer carried out using FLUKA.

Speaker: Mr Nicholas Stoffle (University of Houston)

19 Processing of a structured scintillator for high-resolution X-ray imaging

Structured scintillators coupled with CCDs are promising devices for digital X-ray imaging. These novel X-ray detectors are made by fabrication of high aspect ratio silicon pores by ICP etching, oxidation of the pore walls and finally melting of thallium doped CsI into the pores. In this type of detectors the oxide layer on the pore walls is utilized as the cladding layer similar to optical fibers to confine the produced visible photons inside the pores after the scintillation process. Furthermore, the remaining silicon layer in the middle of the pore walls absorbs the escaping visible photons, effectively reducing the cross talk between the pores. Hence, in this type of detectors outstanding resolutions are provided by only shrinking the lateral dimensions of the pores. In order to investigate the effect of down scaling on the performance of such devices, different silicon pore arrays with different geometries were fabricated with a smallest pitch of 1.4 µm. Preliminary attempts to optimize the filling parameters were carried out and the performance of the structures regarding X-ray absorption and light yield was evaluated. The results show that, simply increasing the melting time and temperature of the filling process increases the likelihood of the loss of thallium dopant in the pores, reducing the light yield. A comparison of the light yield efficiency of the samples demonstrates that the smaller the pores are the less light yield is gained. Yet, a substantially increased absorption length compared to other non-structured, high resolution scintillators will lead to dramatic improvements in the detection efficiency. Since the fabrication method is still immature, further development of the fabrication method might lead to improved yield while increasing the resolution of the device.

Speaker: Mr Yashar Hormozan (Material Physics, KTH)

Slides Presentation2.pptx

20 Simulation of a silicon neutron detector coated with TiB2 converter

Neutron radiation cannot be directly detected in semiconductor detectors and therefore need converter layers. Standard clean-room processes can be used in the manufacturing process of semiconductor detectors with metal layers to produce a cost-effective device. We used the Geant4 Monte-Carlo toolkit to simulate the performance of a semiconductor neutron detector. A silicon photo-diode was coated with vapour deposited titanium, aluminium thin films and a titaniumdiboride (TiB2) neutron converter layer. The neutron capture reaction 10B(n, alpha)7Li is taken advantage of to create charged particles that can be counted. Boron-10 has a natural abundance of about 19.9%. The emitted alpha particles are absorbed in the underlying silicon detector. We varied the thickness of the converter layer and run the simulation with a thermal neutron source in order to find the best efficiency of the TiB2 converter layer and optimize the clean room process.

Speaker: Mr David Krapohl (Department of Information Technology and Media, Mid Sweden University)

21 Optimization of Scintillators for Stacked-layer Detectors of FNGR

For the detection of FNGR(Fast Neutron and Gamma Radiography), usually a plastic scintillator coupled photo-sensor and a CsI crystal scintillator coupled photo-sensor are used respectively for fast neutrons(14 MeV) and gamma-rays(1.17 & 1.33 MeV of Co-60). Owing to the high energy of radiations, the thickness of the scintillator cannot be sufficiently thickened, and the energy cannot be completely absorbed in the scintillator. Although it is optimized, there is dissipation and penetration as much as absorption. This study provides the FNGR detector modules as a stacked-layer structure to be counted at the same time in order to enhance the performance of existing FNGR system. This obtains more absorbed energy penetrated from the existing form of scintillator. As a standard form, BC408 plastic scintillators(2cm x 2cm x 7.5cm) and CsI(Tl) crystal scitillators(1cm X 1cm X 5cm) are simulated for the fast neutron and gamma-ray respectively through the Monte Carlo simulation by the MCNPX and the DETECT97 codes. For the investigation, We have separated the scintillators by pieces in layers to be analyzed with respect to absorbed energy, light generation, and the LTE(Light Transmission Efficiency) of each part to yield the scintillation count of the existing scintillator. Next, we have deducted the optimum thickness of the stacked-layer structure of FNGR in the same manner. The comparison between the existing structure and stacked-layer structure was conducted by evaluating spectrums derived from each condition. The new structure was needed to be more thickened against the existing structure, and 75% and 36% higher efficiencies result for gamma-ray and neutron detection respectively throughout the study. We have planned the experiment with the structure simulated and foresee the possibility of applications for other high-energy radiography systems as well.

Speaker: Mr Jae Hyung Cho (Radiography)

Slides iWoRID13_FNGR_2011_김광현.pptx minitalk_FNGR(1).pptx

22 Optimization simulation of scintillator thickness for Dual X-ray imaging system

A dual X-ray imaging system uses two different energy spectrums that have different penetrative power that are low and high at the same time. It is advantageous in that it reduces the hardening effect of X-ray and creates a clearer image. In this study, it is predicted that electric signal would not be sufficient for the gain caused by the low intensity of the X-ray beam which is decoupled by pre-designed prototype filters. Our research team conducted a study on the optimization of the geometric structures of each scintillator in order to maximize the signals of the scintillator-coupled-detectors. In this simulation, we used a CsI(Tl) scintillator which makes numerous photons when it interacts with the X-ray and used 100kVp X-ray energy which is generally used for bone density measurement, growth plate check, and body fat testing. Then, the filters for separating low and high energies are Er 0.5mm, for the low energy X-ray and a Cu 0.8mm, Rh 0.4mm mix for the high energy X-ray. For the investigation, we separated the scintillators into 10 layers. The analysis was done in terms of the absorbed energy, light generation, and LTE(Light Transmission Efficiency) of each layer to yield the scintillation count of the whole body of existing scintillator. We assumed each sensor area to be 0.32 cm x 0.14 cm pixel through the Monte Carlo simulation MCNPX code to observe the absorbed energy in the scintillator and by the DETECT97 code in order to obtain counts of photons in the sensor. As a result of this study, we determined that the thinner scintillators derive more photons than the thicker existing scintillator. According to the study, optimized thickness of CsI(Tl) scintillator follows 2mm both in low and high energies. To use the result practically, we will compare the existing trade-off method with the newly induced method to verify the consequence by the measurement of electric signals of each condition.

Speaker: Mr Han Gyul Song (Radiography)

Poster 3rd edition

Slides mini talk

23 TSC Measurement of Energetic Levels in Silicon Detector Damaged by Neutrons

This paper presents a measurement of defects in the silicon detector; which is made of high resistivity N type material. The Si detector was exposed in a nuclear reactor to neutron flux and as identification method for created defects in Si detector was applied thermally stimulated current (TSC) measurement. In our case we use a modified method of TSC for a diode with zero bias voltage in the reverse direction. For filling the traps with photoelectric effect is used LED diode with the blue light spectrum. The detector was irradiated with a total dose 1.86.1015 cm-2 of neutrons. Our results were compared with already published data. We made comparison of the TSC measurement after irradiation and after annealing (3-hours) at the temperature of 100°C shows the separation of defects on each of the disorders.

Speaker: Mr Vit Sopko (IEAP CTU in Prague)

24 The effect of laser radiation on CdZnTe radiation hardness.

It was noted that radiation damage occurs in semiconductor radiation detectors during their operation, while measuring ionizing radiation, which impairs the ability of the device [1]. The main expressions of radiation damage are: the increase of leakage current in a semiconductor detector, the need to increase the bias voltage, reduction of the efficiency of collecting the charge created by ionization. The aim of this work is to study the possibility to increase the radiation hardness of Cd0.9Zn0.1Te crystal using laser radiation. Pulsed Nd:YAG laser for this aim was used. Estimation of the crystalline lattice defects before and after irradiation by γ-ray using photoluminescence method in the experiments was applied. Irradiation of Cd1-xZnxTe crystal by γ-ray with of 60Co (E=1.2MeV) a dose rate of 5×105 Rad = 5.0 KGy leads to strongly increase of A0X band intensity in PL spectra of Cd1-xZnxTe crystal by 10 times. In the same time D0X band in PL spectrum of Cd1-xZnxTe crystal disappears fully. We explain it by Cd vacancies generation and localization in the excited luminescence thin layer after γ-irradiation of Cd1-xZnxTe crystal. The main effect observed in the study is suppression of VCd generation and /or localization by γ-radiation at the irradiated surface of Cd1-xZnxTe crystal if the crystal preliminary irradiate by the laser. The phenomenon increases with intensity of the laser in region of the laser intensity up to 0.50 - 2.0 MW/cm2. The intensity of A0X band in PL spectrum of Cd1-xZnxTe crystal increases only 1.7 times (for comparison, non-irradiated by the laser 9.3 times) after γ-radiation if the crystal preliminary was irradiated by the laser at intensity 1.2WM/cm2. The mechanism of this effect is explained in the following way: γ- radiation leads to generation of additional VCd near the surface layer, which causes an increase of A0X band in PL spectrum. Laser radiation has an opposite effect on Cd0.9Zn0.1Te crystal: interstitial Cdi atoms are concentrated near the irradiated surface layer, but vacancies in the bulk of semiconductor according to TGE. This leads to increase of D0X band intensity in PL spectrum. Increase of Cd atoms concentration nearby the surface layer leads to increase of materials radiation hardness because Cd atomic weight is larger comparing to other atoms in Cd0.9Zn0.1Te crystal - Zn and Te [2]. REFERENCES [1] G.Lindstrom, “Radiation damage in silicon detectors,” Nucl. Instr. and Meth. A., V. 512, pp. 30-43, 2003. [2] J. Shapiro, Radiation protection: a guide for scientists, regulators, and physicians, 4¬th ed., 2002, Harvard college, pp. 23-24.

Speaker: Dr Aleksandr Micko (Riga Technical university, Latvia)

Slides The_Effect_of_Laser_Radiation_on_CdZnTe_Radiation_-short_prezentation.ppt

25 Thermal neutron detector based on planar silicon sensor with TiB2 coating

Neutron radiation as a non-ionizing radiation is particularly difficult to detect; therefore conversion material are needed. Conversion materials convert neutrons into secondary charged particles to be detected in silicon sensors. The use of titanium diboride (TiB2) as a conversion material deposited by electron beam-physical vapour deposition (EB-PVD) as a part of front side contact of planar silicon sensor will be presented. Effects of different front side contact material composition and conversion material thickness will be demonstrated and discussed. Sensor behaviour will be examined using alpha particle spectroscopy and a 241Am-Be neutron source. Simultaneously, a Geant4 simulation will be executed to evaluate conversion layer functionality and to discover the conversion material thickness for the best neutron detection efficiency.

Speaker: Mr Tomas Slavicek (IEAP CTU in Prague)

Poster poster_iworid_2011_tomas_slavicek_neutron_detector-final.pdf

Slides short_presentation_Tomas-Slavicek_neutron-detector.pptx

26 The feasibility study on Non-pixel X-ray detector using liquid crystal layer through simulation of transmittance and electric field

In recent times, the study of digital X-ray detector in medical diagnostic has been focused on high resolution image acquisition. The manufacturing methods of digital X-ray detectors can be divided into direct and indirect methods. The indirect system has a low resolution due to blurring of light from scintillator. In contrast, the direct method has higher resolution comparing with indirect method. But it is expensive and having difficult to manufature in large size by using TFT(thin-film-transistor) array. The new fabricated method on medical imaging sensor has been studied variety to compensate these many problems. In this study, the new-concept is proposed for non-pixel X-ray detector by making multi-layer using photoconductor layer and liguid crystal cell used in the display field. The simulations of transmittance and electric field in liguid crystal layer were carried out according to the variation of the applied voltage and photoconductor layer structure. And then, non-pixel X-ray detector film was fabricated by considering the simulated results on liquid crystal cell structure and glass thickness. In the experiment, the linear range of LC twisting was acquired by measure of T-V (Transmittance-Voltage) Curve. The generated voltage from Photoconductor was acquired by changing the glass thickness and the voltage enable LC to twist over 90%. the feasibility of new structure detector was evaluated by using Back Light Unit and X-ray film. In the result of this study, non-pixel detector using liquid crystal cell showed enough feasibility to apply digital X-ray detector.

Speaker: Mr Sung Hun Kim (Biomedical Engineering,Inje University,Obang-dong,Gimhae,Gyeongnam,Republic of Korea)

Poster IWORID_2011_poster_presentation_Kim_Sung_Hun.pdf

27 The design of hybrid x-ray detector using quantum size effect

2-6 group material(e.g. CdTe, CdS, CdSe) is utilized as a photoconductor at the bulk level unlike as a phosphor when manufactured at the nanoscale level. Conceived by this fact, one invented an x-ray detector which hybridized two different kinds of layers from one material, which was acted as a photoconductor in the bulk state and also worked as a phosphor at the nanoscale. This system works as following: First, an x-ray has changed into light on nanoscale phosphor layer, and then the light has been received on photoconductor layer. The emitted light on phosphor layer has the exact wavelength range that is required on a photoconductor. The change of electronic energy level density depending on the size of a crystal within nano-particle affects optical and electrical characteristic variation, which reflects the quantum size effect. On account of this effect, one can utilize two different kinds of layers from one material by regulating the size of the material. As a result of that, by changing emission wavelength with size control of a particle, the most appropriate absorption wavelength to a photoconductor in the bulk state can be emitted on nanoscale phosphor. There seems higher conversion efficiency in the hybrid structure using the same material than using the different materials. Luminescence efficiency of nanoscale phosphor was measured using PL spectroscopy and generated signal from the photoconductor was measured using electrometer and oscilloscope

Speaker: Ji-na Kim (Department of Medical Image Science, Inje University, Gimhae 621-749, Republic of Korea)

Poster IWORID_poster.pdf

28 The development of efficient X-ray conversion material for digital mammography

A variety of direct X-ray conversion materials have been studied to develop digital mammography. Since direct conversion materials, such as HgI2, PbI2, and PbO have high X-ray conversion efficiency comparing to indirect X-ray conversion materials like CsI(Tl) and NaI, direct conversion materials are suitable for digital mammography which requires high spatial resolution at low exposure rate. In this study, a new concept of active matrix flat panel detector for mammography is introduced to fulfill these requirements and reduce physical pains for patient occurred when patients' breast are pressed. This system consists of miniature X-ray tube based on subminiature thermal electron, AMFPI technology besed detector, and a body including automatic position and system control devices. Electrical results from fundamental pixel signal performance of direct X-ray conversion materials on AMFPI are shown and play a important role in verify the functioning of mammographic design. Also, the part of digital X-ray conversion detector can be bent, which serve to reduce patients' breast pain. The results of electrical performances of direct X-ray conversion material, PbO, demonstrate the potential for high efficiency of mammographic systems based on flexible digital mammography. The obtained mammographic images from this system are evaluated and compared to images from existing mammograpic system.

Speaker: Mr Kyung-min Oh (Department of Biomedical Engineering, Inje University, Gimhae 621-749, Republic of Korea)

Slides Iworid_mini_talk.pdf

29 The implementation of photoinduced discharge X-ray detector using photoconductor

This study shows each photoconductor properties of PhotoInduced Discharge X-ray detector. a-Se via former used TFT has many problems. These problems are row yields from TFT manufacture and image quality decrease from its noise. a-Se case especially, duration of manufacture and row yields and circuit damage from high voltage polarizing are significant problems. To overcome problems using a-Se, three types of material are used. Lead Oxide with low leakage current, Mercury Iodide with high sensitivity and mixture of Mercury Iodide are measured with 495~570nm and 620nm Laser. Upper and lower electrode evaporated with Indium thin Oxide by Magnetron Suputtering System are used as a board. Air gap with 100~500nm thickness is used as dielectric. Aluminum board is used at lower substrate. Materials are evaporated by screen printing Method. X-ray reference condition is 70Kvp, 100mA. To find out material properties and electronic properties, Scanning electron microscope, electrometer and oscilloscope are used. A number of materials via PID method has lower leakage current than former used materials. Lead Oxide case ,however, laser response property at 495~570nm and 620nm dose not exist. And Mixtured Mercury Iodide case, laser response property at only 495~570nm exists. only Mercury Iodide has outstanding laser property at both lasers. Though manufactured material from PID method has lower leakage properties than former materials, sensitivity was lower than former materials.

Speaker: YOUNG KYU Lee (Department of Biomedical Engineering, Inje University, Gimhae 621-749, Republic of Korea)

Poster Lee_Young_kyu.pdf

30 The synthesis and characteristics study of radiation phosphors using solution-combustion

X-ray detection, phosphor material of high resolution and high effectiveness has been researched. Rare Earth phosphor material had been used for a long time due to high atomic number and quality efficiency. But, generalization phosphors have a lot of problems with resolution and efficiency that being manufactured by Bulk phosphor. In this paper, Gd2O3:Eu3+, Y2O3:Eu nano phosphor on Europium(Eu) density, calcinations temperature and calcinations atmosphere were investigated to its influence on optical properties. There are various types of synthesizing the nano powder with other materials for the purposes. But in this paper, nano powders of Gd2O3:Eu3+, Y2O3:Eu were synthesized using a solution-combustion method. The synthesized phosphors were characterized by using X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM) and Photoluminescence spectroscopy. At 500℃, the XRD curve showed the phosphors were calcinated and cubic phase. As temperature increase, there is tendency to be cubic-phased. From optical property results, the strongest emission was at 611nm and emission peak was same to commercial bulk phosphors. The strongest luminescent intensity was achieved at 900℃. In this experiment, there was potential to patient dose reduction in the emission efficiency of nano phosphors and improvements in performance could be possible by applying radiation imaging detector.

Speaker: Ms Hye Jin Park (Medical image & science, Inje University, Gimhae, Gyeongnam, Republic of Korea)

Poster iworid_-_PARK_Hye_Jin.pdf

31 X-ray interaction-induced signal and noise characteristics of edge-on silicon microstrip detectors for digital mammography

It has been greatly paid attention in the development of novel x-ray imaging technologies based on single-photon energy measurements for superior image quality with a reduced patient dose. While the promise of this research is exciting, we are at an early stage in the design of energy-resolving detectors. To be successful, it is critical that we fully understand what detector designs have the best chance of success and what designs will never be successful due to fundamental physical or engineering limitations. In the contemporary designs, microstrip silicon detectors having edge-on geometry to the x-ray incidence have been used especially for digital mammography. Using Monte Carlo techniques, we investigate the fundamental signal and noise performances induced by x-ray interactions in the edge-on microstrip detector designs. The response functions are determined and used to determine quantum efficiency, average energy absorption, Swank factor, and detective quantum efficiency based on energy-moment theory. In addition, relative energy accuracy and imprecision in photon-energy measurements are estimated. The results are analyzed with x-ray interaction physics. The spreading of signal and noise through pixel strips due to the Compton scatter is also analyzed. Analyzing approach in this study will be very useful to the better and optimal designs of photon-counting x-ray detectors, such as the optimal tilting angle that may provide the best signal-to-noise performance.

Speaker: Mr Hanbean Youn (School of Mechanical Engineering, Pusan National University)

Poster iWoRID_Poster_EdgeOn_upload.pdf

13:00 Lunch Break

Applications I: 3 contributions

Convener: Dr Wasi Faruqi (MRC Laboratory of Molecular Biology)

32 Synchrotron Radiation in use for cultural heritage studies

The study of Cultural Heritage materials requires advanced techniques to shed new lights on ancient technologies and help in their preservation. The implementation of new analytical tools, including large or medium scale facilities such as synchrotron radiation, charge particle accelerators, neutron sources, etc. permits a deep insight on the archaeological and artistic materials, from the millimeter to the nanometer scales. During this lecture, current applications and potential needs of multiscale imaging techniques will be presented to show the major role played by synchrotron analytical techniques to characterize the nature and the mode of preparation of different pigments, both used for paint or makeup (origin of the minerals, chemical synthesis of new compounds, crushing of crystals, mixing of matters, etc…).

Speaker: Dr Phillippe Walter (CR2MF, Paris, France)

Slides 2011-07_IWORID_Zurich.ppt

33 A Novel Energy-resolving High-speed X-ray Camera as a Powerful Tool in the Full-Field X-ray Analysis of Materials and Biological Samples

A new energy-resolving X-ray camera capable of time-, energy-, and space-resolved measurements has been developed. This new device is built around a high-speed pnCCD detector. A poly-capillary optics can be attached in front of a beryllium entrance window to conduct X-ray photons from the probe to distinct pixels onto the detector. For the detection of light elements, a thinner Be-window can be chosen. The pnCCD has an active area of 12.7 x 12.7 mm2, 264 x 264 pixels with 48 µm square pixel size. The column-parallel and spilt-frame readout enable frame rates exceeding 400 Hz (equivalent to 28 Mpixel/s) and a maximum count rate of 620 kcps. The spectroscopic performance at this speed is around 150 eV (FWHM) for Mn-Kα. The full depletion of detector volume enables quantum efficiencies approaching 100 % in the 1 keV-10 keV energy range and is still amounting to 22 % for 24 keV photons. The camera is capable of fast acquisition of spatially and energy resolved fluorescence images. A dedicated software enables the acquisition and the online processing of the spectral data for all 69696 pixels, leading to a real-time visualization of the elements distribution in a sample. We present measurements with synchrotron radiation and laboratory sources showing the camera capability of performing full-field X-ray Fluorescence (FF-XRF), full-field total-reflection XRF (TXRF), X-ray Diffraction (XRD) and X-ray fluorescence Tomography. Examples from applications in biological sciences are also given.

Speaker: Mr Ivan Ordavo (PNSensor GmbH)

34 Low-energy X-ray detection with an in-vacuum PILATUS detector

The feasibility of using PILATUS single-X-ray-photon counting detectors for long-wavelength macromolecular crystallography was investigated by carrying out a series of experiments at the Diamond Light Source. Results on detection threshold equalization at low-energy (with 2.3 to 3.7 keV X-rays) obtained with a PILATUS operated in helium environment were presented in reference [1]. To complement this study, a PILATUS detector was recently tested in-vacuum on the test beamline B16 of the Diamond Light Source. The PILATUS detector was exposed to monochromatic X-rays with an energy of 2.5 keV and 3 keV. Effects of detector cooling on noise performance, energy calibration and threshold trimming were investigated. When detecting 3 keV X-rays, the electronic noise of the analogue output of pixel preamplifiers forces the threshold to be set at a higher level than the recommended 50% energy level which minimizes charge-sharing effects. The influence of non-optimum threshold setting at low X-ray energy was studied by characterizing the detector response to a collimated beam of 3 keV X-rays scanned across several pixels. [1] J. Marchal and A. Wagner, “Performance of PILATUS detector technology for long wavelength macromolecular crystallography”, Nucl. Meth. Phys. Res A (2010), doi:10.1016/j.nima.2010.06.142

Speaker: Dr Julien Marchal (Diamond Light Source)

Slides Marchal_Julien_IWORID2011.ppt

35 Patient position verification in ion beam therapy using pencil beam radiography

The basic rationale for radiation therapy using ion beams is its high local precision of dose deposition. Due to the steep gradients in dose distribution precise knowledge of the patient's position and potential tumor displacement becomes even more important than in conventional therapy using photon beams. Therefore accurate patient positioning prior and during beam application is a crucial part of the therapy. The current standard position verification procedure uses X-ray based imaging before each beam application assuming the patient to remain in his position. During irradiation there is no possibility to monitor the patient position or organ movement. The aim of this study is to investigate the possibility of verifiying the position of a fiducial marker during therapy with a narrow pencil beam. This method may be much faster than X-ray imaging and irradiates only very little tissue. Some modern ion therapy facilities like the Heidelberg Ion Therapy Center (HIT), where our measurements were carried out, use scanning pencil beams to apply dose. Exploiting them for imaging allows to solely irradiate regions of interest in the patient's body, e.g. tissue containing medical seeds or bony structures. This can be done quickly in turn with therapeutical beam application. Due to the high atomic number, metal markers provide much higher contrast than organic structures. For our measurements we used segmented gold and NiTi seeds of sizes up to 3x1 mm² embedded in a cuboid PMMA phantom. To image the residual beam we used the Perkin Elmer RID256-L flat panel detector. It has a pixel pitch of 800 µm and provides an active area of 20x20 cm². Measurements showed that 10^4 particles of a 300 MeV/u carbon ion beam suffice to make the seed's position visible at different material depths with an uncertainty of 1 mm. While the dose is similar to an X-ray image, the irradiated volume is very much reduced. In this work it was shown that imaging of seeds and landmarks by ion pencil beams and a flat panel detector is technically feasible. We are currently working on a comparison of the results with measurements performed using the Timepix detector, developed by the Medipix collaboration, where we expect even better performance due to the smaller pixel pitch and the possibility to distinct particles. Using this detector would in principle allow to reduce the dose considerably.

Speaker: Mr Lucas Huber (German Cancer Research Center (DKFZ))

Slides 04_presentation_iworid_02.pptx

15:35 Coffee Break

Poster Mini Talks II

Convener: Dr Wasi Faruqi (MRC Laboratory of Molecular Biology)

36 Application of 3D sensitive voxel detector for X-ray color imaging and beam hardening effect correction

The X-ray imaging is today widely used in broad area of applications. One of the X-ray imaging limitations is in distinguishing between thick layer of low Z and thin layer of the high Z material. The background effect is called Beam hardening. It is the effect where the incident X-ray spectrum is modified by the object itself according to its material composition and thickness. This causes problems in many applications e.g. CT reconstruction where it leads to reconstruction artifacts and lower resolution. This work presents a new technique for estimation of beam hardening using a new 3D voxel detector based on Timepix chip. The device is designed as a layered stack of several Timepix pixel detectors. The single Timepix device (256 x 256 pixels with pitch of 55 µm) consists of sensor chip (typically 300 µm of silicon) bump bonded to a readout chip (typically 700 µm). The readout chip is thinned down to 120 µm to reduce amount of insensitive absorbing material in the stack. Individual layers in the stack act as a filter, i.e. each stack layer visualize different part of the spectra attenuated by the object giving further information about the object composition. Comparing attenuation levels observed in different detector layers can be used to estimate the level of a beam-hardening effect in the imaged object and thus to distinguish differences in material composition.

Speaker: Dr Pavel Soukup (IEAP CTU in Prague)

Slides Soukup_iworid_2011_minitalk.ppt

37 Characterisation and image correction of Hamamatsu C9730DK-10 flat panel X-ray imaging detector

CMOS flat panels are becoming standard equipment of X-ray micro-imaging laboratories. It is a mature technology that provides very good spatial resolution, dynamic range and large sensitive area. An example of such detector is the Hamamatsu C9730DK-10 flat panel. It comprises of a CsI:Tl scintillator directly deposited on the two-dimensional photodiode array (pixel size of 50 x 50 µm, total sensitive area 52.8 x 52.8 mm). The charge accumulated in each pixel is transferred to amplifiers and converted to a voltage signal. The analogue signal is subsequently digitized by a 14-bit analogue-to-digital converter and sent to PC via USB interface. The modulation transfer function, linearity, dynamic range and signal-to-noise ratio were measured and compared with manufacturer’s specifications where applicable. The signal-to-thickness calibration is an image correction method that replaces the standard flat field correction. It was originally developed for the single photon counting detectors Medipix. The signal-to-thickness calibration method was implemented in our in-house software platform for use with the flat panel. Performance of this correction method and a set of sample images corrected by the signal-to-thickness calibration will be presented.

Speaker: Dr Josef Uher (CSIRO PSE)

Slides 2011-06-10_FP_characterisation_mini-talk.pptx

38 Design, Construction and Test of a precursor GEM-TPC for PANDA

High-precision spectroscopy of hadrons in the strange and charm sector, as envisaged in the PANDA experiment requires an excellent charged particle tracking system with multiple track identification (up to 4000 tracks superimposed inside the TPC all the time), high spatial resolution (σrϕ~150 μm,σz~1mm),high momentum resolution (~1%),minimal material budget (~1% of radiation length),high rate capability, resistance against aging, etc. Therefore, a cylindrical Time Projection Chamber(TPC)was proposed as the central tracking detector for PANDA.In addition to its excellent tracking properties, a TPC would strongly improve particle identification (PID) in the sub-GeV region, which is very important for most of the interesting physics channels and for rejection of low momentum pions from ppbar annihilation. Owing to the beam properties at the High Energy Storage Ring (HESR), the TPC has to operate at high particle rates and in a continuous mode, i.e. without gating. The use of GEM foils as amplification stage instead of conventional MWPC’s allows us to bypass the necessity of a gating structure, as the back drift of ions into the drift volume has been shown to be intrinsically suppressed due to the asymmetric internal field configuration in a GEM-based gas amplification system. A large prototype detector has been designed, built and tested. The prototype has been commissioned with cosmic rays before it was installed in the FOPI experiment at GSI at the end of 2010. The application of the prototype in a running physics experiment constitutes a very useful test and provides valuable data on the tracking performance of an ungated GEM-TPC in PANDA. For FOPI, in turn, the TPC will provide a significant improvement for the detection of Λ-vertices. Here the design of the prototype, the front-end and readout electronics employed, and present first results obtained during the beam test in FOPI will be presented.

Speaker: Mr Rahul Arora (GSI Helmholtzzentrum für Schwerionenforschung GmbH)

39 Effect of charge transfer mechanisms on the charge transfer inefficiency of charge-coupled devices used as particle detectors

Radiations have effect on charge-coupled devices used as particle detectors. Many electrical characteristics in these devices are affected such as dark current and charge transfer inefficiency (CTI). In this work we will study the effect of traps, created after irradiating CCD, on the CTI. In previous works [1-2], we have used simple analytic models by including some timing parameters. To add more interesting parameters, the analytic modeling becomes difficult or impossible, hence the need of numerical modeling. A simple numeric model is used to study the effect of traps on the CTI with taking into account the effect of charge transfer mechanisms (self-induced drift, fringing-field drift and thermal-diffusion) in contrast to the analytical modeling where we have neglected them. This study allows the determination of the frequency limit where the charge signal is not well transferred even with the presence of low density of traps. The CTI as a function of temperature is also presented. References [1] A. Sopczak et al., “Simulations of the Temperature Dependence of the Charge Transfer Inefficiency in a High-Speed CCD”, IEEE Trans. Nucl. Sci., vol. 54, no. 4, pp. 1429–1434, 2007. [2] A. Sopczak et al., “Modeling of Charge Transfer Inefficiency in a CCD With High-Speed Column Parallel Readout”, IEEE Trans. Nucl. Sci., vol. 56, no. 3, pp. 1613–1617, 2009.

Speaker: Dr Khaled Bekhouche (LMSM laboratory, Biskra University, Algeria)

40 Image processing for X-ray transmission radiography with 3D voxel detector

The first prototype of a 3D voxel detector was recently developed as a layered stack of several Timepix pixel detectors. The single Timepix device (256 x 256 pixels with pitch of 55 µm) consists of a sensor chip (typically silicon 300 µm thick) bump bonded to a pixelated readout chip. The readout chip is thinned down to 120 µm to reduce the amount of insensitive material in the stack. The voxel detector can be used in many particle tracking applications and it has also many advantages in conventional X-ray transmission radiography as well. Imaging with such device brings a lot of benefits such as higher detection efficiency, improved spatial resolution, presence of a directional information and mapping of beam-hardening effects. During radiographic measurement the voxel detector is operated in integrating (counting) mode. The acquired information has the form of a 3D matrix containing the number of X-ray photons registered by individual volume elements - voxels. In order to retrieve an image from such data a number of correction and processing steps has to be applied: 1. Corrections of response of individual voxels: Each voxel is connected to its own analog processing chain, therefore, the response of all voxels is never fully uniform. This non uniformity has to be determined and corrected. 2. Detector alignment corrections: The individual detector layers are physically slightly shifted and rotated to each other due to imperfection of the device assembly. 3. Beam geometry determination: The distance and position of the X-ray source is determined from the measured data. 4. Evaluation of the beam hardening effect: Comparing attenuation levels observed in different detector layers can be used for the estimation of the level of the beam-hardening effect in the imaged object. 5. Assembling of final image(s). All information acquired in steps 1-4 is used and the final image is produced. In terms of image processing, most of the described correction steps result in a series of affine transformations between images from individual detector layers. These affine warps are found using Lucas-Kanade algorithm based on the least square optimalization. The result of data processing is not only an assembled image of a transmitted object but also the position of X-ray source relative to detector which is very useful in many applications (e.g robotic CT). Results together with evaluation of the techniques are demonstrated on radiogram of real samples.

Speaker: Mr Ivan Jandejsek (Institute of Experimental and Applied Physics, CTU in Prague)

Slides Mini Talk

41 Overview of the R&D program on liquid Argon TPC's under development at the University of Bern

The liquid Argon Time Projection Chamber (TPC) technique is a promising technology for future large-size neutrino detectors. At LHEP of the University of Bern (Switzerland) R&D projects towards large detectors are going on. The main goal is to prove the feasibility of very large detectors (>50kt) with long drift path, more than 10 meters. Therefore we build a liquid Argon TPC with 5 m drift distance. Many other aspects of the liquid Argon TPC technology are also under investigation, as a new device to generate high voltage in liquid Argon, a recirculation filtering system and the multi-photon ionization of liquid Argon with DUV laser has been measured. In the talk two types of detectors will be presented: A small size prototype liquid Argon TPC for specific detector technology studies and ARGONTUBE, a 5 m long liquid Argon TPC.

Speaker: Mr Marcel Zeller (LHEP University of Bern)

Slides Poster030711presentation.pptx

42 Silicon Sensor Developments for the CMS Tracker Upgrade

CMS started a campaign to identify the future silicon sensor technology baseline for a new Tracker for the high-luminosity phase of LHC. We ordered a large variety of 6” wafers in different thicknesses and technologies at HPK. Thicknesses ranging from 50µm to 300µm are explored on floatzone, magnetic Czochralski and epitaxial material both in n-in-p and p-in-n versions. P-stop and p-spray are explored as isolation technology for the n-in-p type sensors as well as the feasibility of double metal routing on 6” wafers. Each wafer contains different structures to answer different questions, e.g. geometry, Lorentz angle, radiation tolerance, annealing behavior, read-out schemes. Dedicated process test-structures, as well as diodes, mini-sensors, long and very short strip sensors and real pixel sensors have been designed for this evaluation. This contribution provides an overview of the individual structures and their characteristics and summarizes interesting measurements performed so far.

Speaker: Mr Georg Auzinger (CERN)

Slides poster_talk.pdf

43 Characterization and MCNP simulation of Neutron Energy Spectrum shift after transmission through strong absorbing materials and its impact on tomography reconstruction image

An ideal neutron radiograph used for quantification and 3D image tomography reconstruction should be a transmission image, which exactly obeys the exponential law of attenuation with a monochromatic neutron beam. There are many reasons, why this assumption does not hold for high neutron absorbing materials. The main deviations from the ideal are due essentially to neutron beam hardening effect. The main challenges of this work are the characterization of neutron transmission through boron alloyed steel material and the study of beam hardening effect on neutron transmission tomography image appearance of a sample made essentially from this material. MCNP and FBP simulation were performed to adjust linear attenuation coefficients data and to perform 2D topographic image reconstruction with and without beam hardening corrections. A suitable beam hardening correction procedure was developed and applied. The results of 2D images reconstruction of original and corrected projections data obtained were qualitatively and quantitatively compared.

Speaker: Dr Faycal KHARFI (Nuclear Research Centre of Birine, Algeria)

44 Super Resolution and Criteria for best dynamic imaging capability with a neutron CCD camera used for dynamic process image capture and analysis

Neutron imaging is a powerful method for non-destructive investigations where high penetration through metals and in particular high contrast for hydrogenous materials maybe exploited. Due to the complexity of digital neutron static or video image formation, image capture conditions and parameters must be accurately selected. In this work, experimental acquisition conditions in terms of integration time (τ) and signal gain (G) for optimum neutron video capture of water flow processes inside metallic pipe system were studied and established according to the neutron source properties and CCD camera electronic characteristics. Neutron imaging experiments were performed at the neutron radiography facility of the Algerian Es-Salam research reactor. Compromises between integration time, signal gain in one side and dynamic range and neuron source intensity in another side were established allowing optimum video sequence capture conditions. A post acquisition super resolution processing procedures were also applied to improve the quality of the video sequences obtained.

Speaker: Dr Faycal KHARFI (Nuclear Research Centre of Birine, Algeria)

45 Practical expressions describing detective quantum efficiency in flat-panel detector

Due to the health risks associated with exposure to radiation, technical excellence in medical imaging is critical to high-quality medical care. In radiology, image quality excellence is a balance between system performance and patient radiation dose, hence x-ray systems must be designed to ensure the maximum image quality is obtained for the lowest consistent dose. The concept of detective quantum efficiency (DQE) is widely used to quantify, understand, measure, and predict the performance of x-ray detectors and imaging systems. Cascaded linear-systems theory can be used to estimate DQE based on the system design parameters and this theoretical DQE can be utilized for determining the impact of various physical processes, such as secondary quantum sinks, noise aliasing, reabsorption noise, and others. However, the prediction of DQE usually requires tremendous efforts to determine each parameter consisting of the cascaded linear-systems model. In this study, simple, practical DQE formalisms assessing photoconductor- and scintillator-based flat-panel detectors under typical operation conditions, such as quantum-limited operation, are described. The developed formalisms are validated by comparing the measured DQE values and discussed for their limits. This study will be very useful for the rapid prediction of the DQE performances of developing systems as well as the optimal design of systems.

Speaker: Prof. Ho Kyung Kim (Pusan National University)

Poster Poster_HK_Upload.pdf

Sensor Materials, Device Processing & Technologies II: 2 contributions

Convener: Prof. Val O'Shea (University of Glasgow)

46 Wafer Level 3D Integration Technologies

Wafer level packaging processes has been used over several years in hybrid pixel module manufacturing. Deposition processes like electroplating, sputtering as well as evaporation are well established technologies for the formation of interconnection structures on readout chip wafers as well as on sensor wafers. Following the packaging roadmaps to higher integration, increased functionality and a reduction in size 3D wafer level packaging technologies come into the focus of technology development. The formation of Through Silicon Vias (TSVs) is a key technology for the fabrication of 3D architectures on wafer level. Therefore new concepts of wafer thinning, thin wafer handling and via filling processes have to be developed. An overview of 3D integration technologies will be given focusing on the special requirements for pixel module fabrication. Chip size packages for different applications using 3D wafer level integration technologies were fabricated at Fraunhofer IZM. Examples of 3D chip size packages using TSV technology will be described in detail in this presentation.

Speaker: Thomas Fritzsch (IZM Dept. High Density Interconnect & Wafer Level Packaging)

47 Cadmium Telluride pixel sensor development for high sensibility X-ray imaging device

Single X-ray photon counting pixel detector was expected to be a next generation 2D X-ray detector from the early stage of the third generation synchrotron radiation facilities. In fact, silicon-based hybrid pixel detectors such as PILATUS became commercially practical. To improve the detection sensibility in the high energy X-ray region, cadmium telluride (CdTe) is regarded as a promising semiconductor sensor material because of its high density and high atomic number. Therefore, we are developing CdTe-based pixel sensors and their readout ASICs for synchrotron radiation application. We have investigated three-type electrode configurations of the ohmic contact structures on both sides with platinum electrodes (Type-1), a Schottky contact with an indium common electrode on the front side (Type-2), and a Schottky contact with aluminum electrodes on the pixel side (Type-3). Type-2 is operated in the hole-collection mode. On the other hand, Type-3 is operated in the electron-collection mode. Type-3 is expected to realize much superior performance because of the higher mobility of electrons than holes. We designed and fabricated a prototype of a CdTe pixel detector (SP8-01). The format was 16 pixels × 16 pixels with a pitch of 200 μm × 200 μm. The sensor thickness was 500 μm. A full-custom ASIC with TSMC 0.25 μm technology was designed as a readout circuit, which is equipped with a preamplifier, a shaper, a window-type discriminator and 20-bits counter. The sensors were bump-bonded to the ASIC chips by a gold-stud bonding technique. Operation temperature dependence study was performed by placing the type-3 prototype in a thermostatic chamber. The temperature was controlled at -20, -10, 0, 10 and 20 degree and the detector was irradiated with X-rays from 241-Am radio-isotope. Charge collection and energy resolution characters were examined by continuous threshold scans. The performance deteriorated in a short time and discontinuity behavior　happened at 20 degree. On the other hand, the detector attained a long-term stable operation at lower temperatures. We submitted the next step SP8-02 prototype with the same architecture for ASIC, but with the pixel format of 50 × 20. We could not achieve any valuable result for ohmic and indium-Schottky sensors in SP8-01 because of vendor failures in processing the In/Au stud bonding unfortunately. Three type sensors will be processed to try again in SP8-02.

Speaker: Dr Hidenori Toyokawa (Japan Synchrotron Radiation Research Institute)

Slides iWoRID_toyokawa.pdf

48 CdTe Medipix2 and Medipix3 Pixel Detectors: Material Characterization, Technology and Device Performance

The development of pixel detector arrays for different types of applications requires sensors with high efficiency and high homogeneity. The efficiency is strongly depending on the absorption of the detector material. High-Z semiconductors like CdTe-based materials are the most promising ones. The recent progress of CdTe crystals and the availability of interconnection technology open the possibility of processing CdTe detectors with small pixels down to 55 µm and high efficiency for X-ray energies above 20 keV. CdTe and CdZnTe detectors have been studied for several years. In the last years the technology for hybridization of CdTe based pixel detectors was developed for small pixel pitches. Different types of pixel detectors have been produced using our own technology with small pixels down to 55 µm and high connection density up to 65,000 pixels. CdTe wafers up to 3 inch diameter have been used for processing the pixel detectors. Detectors with a size of 14x14 mm² and 42x28 mm² were developed using the Medipix2. The assemblies were tested with different radiation sources, X-ray tubes and by Synchrotron radiation. The obtained results regarding the efficiency, the homogeneity and the spectroscopic features are discussed in comparison with the data of material characterization before and after processing. Preliminary results of the performance of the pixel detector systems with Medipix3 will be presented.

Speaker: Dr Michael Fiederle (Freiburger Materialforschungszentrum FMF)

Slides IWORID_Fiederle_Medipix3_2011.pptx (Protected)

Poster Mini Talks III

Convener: Prof. Val O'Shea (University of Glasgow)

49 Refraction contrast imaging and edge effects in neutron radiography

Following the achievements in X-ray imaging several new imaging modalities have been demonstrated recently in thermal and cold neutron radiography. In addition to conventional radiography and tomography based on neutron absorption contrast both propagation and grating-based diffraction contrast as well as phase contrast imaging has been demonstrated with neutrons providing unique non-destructive testing techniques that are complimentary to the X-ray results. In addition, the interaction of neutron spin with magnetic fields enable a unique method of imaging magnetic fields. Existence of both absorption and refraction contrasts in neutron radiographic images has been observed with certain materials and geometries, e.g. aluminum and steel objects with flat and curved surfaces illuminated at grazing incidence. In this paper we describe the edge enhancement and refraction/scattering effects in neutron radiography measured at thermal and cold neutron beams with a high resolution microchannel plate neutron counting detector. These effects in some cases can enhance the contrast of certain features in the neutron radiographic images. At the same time, the same effects introduce image distortions, as in case of tomographic reconstructions. We also demonstrate how novel microcapillary neutron collimators can enable refraction and scattering contrast imaging in some cases, where the refraction and scattering angles are relatively large. These collimators can also be used to reduce some refraction artifacts, namely remove bright edges in the transmission images.

Speaker: Dr Anton Tremsin (University of California at Berkeley)

Slides A.S.Tremsin_Minitalk.ppt

Tomogaphy BeadsWithCollimator_RatioTiltedToPeakTransm.wmv

tomography Tomo_Beads1.wmv

50 ATLAS Silicon Microstrip Tracker Operation and Performance

The SemiConductor Tracker (SCT), comprising of silicon micro-strip detectors is one of the key precision tracking devices in the ATLAS Inner Detector. ATLAS is one of the experiments at CERN LHC. The completed SCT is in very good shapes with 99.3% of the SCT’s 4088 modules (a total of 6.3 million strips) are operational. The noise occupancy and hit efficiency exceed the design specifications. In the talk the current status of the SCT will be reviewed. We will report on the operation of the detector, its performance and observed problems, with stress on the sensor and electronics performance. In December 2009 the ATLAS experiment at the CERN Large Hadron Collider (LHC) recorded the first proton-proton collisions at a centre-of-mass energy of 900 GeV and this was followed by the unprecedented energy of 7 TeV in March 2010. The Semi-Conductor Tracker (SCT) is the key precision tracking device in ATLAS, made from silicon micro-strip detectors processed in the planar p-in-n technology. The signals from the strips are processed in the front-end ASICS ABCD3TA, working in the binary readout mode. Data is transferred to the off-detector readout electronics via optical fibers. The completed SCT has been installed inside the ATLAS experimental hall since 2007 and has been operational since then. Calibration data has been taken and analyzed to determine the noise performance of the system. In addition, extensive commissioning with cosmic ray events has been performed both with and without magnetic field. The sensor behavior in the 2 Tesla solonoidal magnetic field was studied by measurements of the Lorentz angle. After this commissioning phase, the SCT was ready for the first LHC pp collision run. We find 99.3% of the SCT modules are operational, noise occupancy and hit efficiency exceed the design specifications, the alignment is already close enough to the ideal to allow on-line track reconstruction and invariant mass determination. In the talk the current status of the SCT will be reviewed, including results from the latest data-taking periods in 2009 and 2010, and from the detector alignment. We will report on the operation of the detector including overviews on services, connectivity and observed problems. The main emphasis will be given to the performance of the SCT with the LHC in collision mode and to the performance of individual electronic components. The SCT commissioning and running experience will then be used to extract valuable lessons for future silicon strip detector projects.

Speaker: Ms Miho Yamada (KEK)

Slides ATL-INDET-SLIDE-2011-302.pdf

51 An Optimised System for Measurement of Radon Levels in Buildings by Spectroscopic Measurement of Radon Progeny

Radon gas, 222Rn, is a problem in many buildings. The radon gas is not harmful in itself, but the decay chain contains charged elements as 218Po, and 214Po ions which have a tendency to stick to the lungs. Alpha particles from the decay of these ions cause damages to the lungs and increase the risk of lung cancer. Exposure to radon is estimated to cause between 3-14% of all lung cancer cases, depending on the average concentration in the country. Recently the limits for radon levels in buildings have been reduced by the World Health Organisation, to 100Bq/m3, increasing the need for fast and efficient methods to measure radon levels. The initial decay of 222Rn occurs in free air and could be detected using the principle of an ion chamber. However some of the decay products are charged and can be electrostatically collected on a semiconductor detector where further decays are easily detected. In this project we have developed a method to measure the decay of 218Po, and 214Po using a semiconductor detector with spectroscopic readout. These results could then, in combination with information on temperature and humidity, be used to calculate the original content of 222Rn in the air. The system for measuring the radon progeny consists of a metal net cage, a silicon detector and spectrum analysing readout electronics. Radon diffuses into the cage and the radon progeny from the decays inside the cage is electrostatically collected on a silicon detector connected to spectrum analyser electronics. It is then essential to measure the ratio between the two energy peaks to verify that the counts results from 222Rn decays inside the cage. An excess amount of 214Po decays indicate that isotopes from decays outside the cage are collected on the detector. The system, which also contains sensors for temperature and humidity, is relatively fast and can be used both for measuring radon content and for controlling ventilation systems. In the current project we have tested different cage volumes, detector sizes and collection voltages to optimise the system. In addition the effects of humidity and temperature have been verified with the optimised system.

Speaker: Anna Fröjdh (Mid Sweden University)

Slides Poster_Mini_Talk_-_annafr.pptx

52 Calibration and Performance of the precision chambers of the ATLAS muon spectrometer.

The ATLAS muon spectrometer consists of a system of precision tracking and trigger chambers embedded in a 2T magnetic field generated by three large air‐core superconducting toroids. The precision Monitored Drift Tube (MDT) chambers measure the track sagitta up to a pseudo‐rapidity of 2.7 with a 50 μm uncertainty yielding a design muon transverse momentum resolution of 10% at 1 TeV. Muon tracking is augmented in the very forward region by Cathode Strip Chambers (CSC). The calibration program, essential to achieve the spectrometer design performance and physics reach, is conducted at three worldwide computing centers. These centers each receive a dedicated High Level Trigger data stream that enables high statistics based determination of T0's and drift‐time to drift‐space relations. During the first year of data taking a system of periodic calibration updates has been established. The calibration algorithms, methods and tools and performance results for this first year of LHC collision data collected by the muon spectrometer will be presented.

Speaker: Dr Felix Rauscher (Ludwig-Maximilians-Universität München)

Poster http://cdsweb.cern.ch/record/1361329/files/ATL-MUON-SLIDE-2011-306.pdf?version=1

Slides beamer.pdf

53 High resolution X-ray imaging based on single crystal films

In a high-resolution (micrometer spatial resolution) X-ray imaging detector [1], the Single Crystal Film (SCF) is the first element of the detection chain. Its role is crucial as its efficiency and thickness directly impacts the Detective Quantum Efficiency (DQE) of the detection system. The ideal SCF should possess high absorption efficiency, high light output, low afterglow, optical match with the detector and it should be grown on a substrate free from background luminescence [2]. SCFs are produced by the vertical Liquid Phase Epitaxy (LPE) technique in a thickness range from 1µm to 30µm with good optical quality. At the European Synchrotron Radiation Facility (ESRF), a LPE laboratory was built in order to produce common SCFs for synchrotron beamlines, as well as to develop denser and more efficient SCFs for the future. The laboratory and its equipment will therefore be presented. Properties of common SCFs (GGG:Eu [2], GGG:Tb, LSO:Tb [3], [4], [5]) will be compared and the consequence of those properties on the detection system in terms of DQE will be highlighted. Finally the emphasis will be put on the coupling of the SCFs to the optics and CCD camera, in order to optimize the detection system as a whole. [1] A. Koch and al., SPIE, vol. 3659, pp 170-179 (1999). [2] T. Martin and al., J. of Synchrotron Radiation, vol. 13, pp 180-194 (2006). [3] T. Martin and al., IEEE Transactions on Nuclear Science, vol. 56, pp 1412-1418 (2009). [4] P.-A. Douissard and al., J. of Synchrotron Radiation (2010). [5] www.scintax.eu/

Speaker: Paul-Antoine Douissard (ESRF)

Transparents LPE_IWORID2011_minitalk_1.pdf

54 Development of ultra-sensitive radon detector for SuperNEMO experiment

Neutrinoless double beta decay (0nuBetaBeta) is a problem of great interest in particle physics (e.g.[1], [2]). It is the best process to study the nature of the neutrino (Dirac or Majorana particle) and could clarify its mass scale. This year the NEMO collaboration [3] has finished main R&D of the SuperNEMO detector design to improve the sensitivity to T1/2(0nu) to the level of ~10^26 years [4]. The construction of the first SuperNEMO detector module (demonstrator with 5-7 kg of enriched 82Se isotope) has already started. One of the most important source of radioactivity is the radon gas and its daughter products.The radon activity in the tracking volume of its predecessor NEMO-3 detector has been reduced significantly (to 6.5 mBq/m3) after installation of an antiradon facility (providing a continuous flow of air 150 m3/hour with a radon level ~1 mBq/m3). For measurement of the radon activity at the output of the antiradon facility the 70-litre detector [5] developed for the SuperKamiokande experiment is used. Its sensitivity (1 mBq/m3 corresponds to 1 detected event per day) is not sufficient for purposes of the SuperNEMO detector. To be able to measure lower radon activities (below 1mBq/m3) in reasonable time of measurement the development of new ultra-sensitive radon detector is currently carried out. Our R&D towards such sensitive radon detector started in 2010. The detection is based on electrostatic collection of radon progenies (214Po, 218Po) on Si PIN diode. The same approach was selected for 718-litre radon detector [6], which provides the detection limit for air as 0.7 mBq/m3 for one-day measurement. The detector is made of stainless steel using 6 kV high voltage. During last year our R&D was devoted to the improvement of collection efficiency by testing of different geometrical shapes of the detector volume (cylindrical, spherical, cubical), location of the Si PIN diode, different HV (up to 30 kV) and material of the detection vessel (stainless steel, wire net). The tests show that the optimal detector vessel should be hemisphere with smaller volume of 50 l using HV as high as possible (e.g. 25 kV, because no saturation was observed). The results of R&D (comparison of obtained efficiencies for different geometrical shapes as well as HV) will be presented. Based on our tests two prototypes of high sensitivity radon detector with volumes of 50 l and 200 l were constructed as first steps towards 1m3 detector which will be divided into smaller subdetectors providing high efficiency of detection. The first prototype has hemispherical shape and is made of stainless steel. The second prototype is stainless steel box (200 l volume). Its volume is divided into 4 independent submodules (made of wire net) with hemispherical shape using high voltage (25 kV) for electrostatic collection of radon progenies at Si PIN diodes (also 4 pieces). At present, the long term measurement of the background is performed. As next step we plan to measure the efficiency of the apparatus using stable Rn source with known activity. Both prototypes and the results of testing (efficiencies, background level) will be presented. References: 1. H.V. Klapdor-Kleingrothaus et al., Phys. Rev. D 63 (2001) 073005. 2. S.M. Bilenki et al., Phys. Rev. D 64 (2001) 053010. 3. R. Arnold et al., Nucl. Instr. Meth. A536, 79 (2005). 4. E. Chauveau, AIP Conference Proceedings 1180, (2009) 26. 5. Y. Takeuchi, et al., Nucl. Instr. And Meth. A 421 (1999) 334. 6. C. Mitsuda et al., Nucl. Instr. And Meth. A 497 (2003) 414.

Speaker: Mr Fadahat Mamedov (Institute of Experimental and Applied Physics, CTU in Prague)

Slides IWORID_info_FM_Prague.pptx

55 Evaluation of a CCD X-ray Imaging Detector with the Medipix2 Detector

Over the last decades the traditional photographic films used in radiology have been replaced by the digital X-ray imaging sensors. The main advantages of these systems are their detection efficiency of the image acquisition and the ability to directly digitally transfer and enhance obtained images. In this paper we characterize and evaluate the X-ray imaging performance of a YAG single crystal scintillator based optical camera. The camera uses a CCD sensor of size 36x36mm2 with 16 million pixels of 9x9 µm2 pitch. For the evaluation of the imaging capabilities of this camera the semiconductor pixel detector Medipix2 was used. The imaging capability is evaluated in terms of several basic characteristics: spatial resolution, edge response function, signal to noise ratio and contrast to noise ratio. Moreover the detection efficiency in the energy range 1-60keV was studied in order to determine the most suitable energetic range. A microfocus X-ray tube was used for high spatial resolution measurements in order to minimize the influence of the X-ray tube spot size. A set of testing measurements was done on edge phantom, step phantom wedge and low contrast fibres. The corresponding measurements for all systems were held under identical conditions in order to assure comparability. The results measured by the CCD camera demonstrate the possibility of a sensitive X-ray radiography imaging with high spatial resolution.

Speaker: Jan Tous (Crytur, Ltd.)

Slides Presentation_Tous.ppt

56 Operational experience with the ATLAS Pixel Detector at the LHC.

The ATLAS Pixel Detector is the innermost detector of the ATLAS experiment at the Large Hadron Collider at CERN, providing high-resolution measurements of charged particle tracks in the high radiation environment close to the collision region. This capability is vital for the identification and measurement of proper decay times of long-lived particles such as b-hadrons, and thus vital for the ATLAS physics program. The detector provides hermetic coverage with three cylindrical layers and three layers of forward and backward pixel detectors. It consists of approximately 80 million pixels that are individually read out via chips bump-bonded to 1744 n-in-n silicon substrates. In this talk, results from the successful operation of the Pixel Detector at the LHC will be presented, including monitoring, calibration procedures, timing optimization and detector performance. The detector performance is excellent: 97,5% of the pixels are operational, noise occupancy and hit efficiency exceed the design specification, and a good alignment allows high quality track resolution.

Speaker: Mr Marcisovsky Michal (IoP ASCR PRague)

Slides PixelMiniTalk_Marcisovsky.pdf

57 SURFACE STATE EFFECTS ON N+P DOPED ELECTRON DETECTOR

There is an ever growing need for highly effective electron detectors with high responsivity. One of the parameters that has been shown to have a negative influence on the responsivity of a radiation detector is the surface recombination velocities of minority carriers at the Si-SiO2 interface. With the n+p detector discovered to possess better responsivity than a p+n detector at any given interface recombination velocity or fixed oxide charge Qf, there is a need to further investigate the n+p detectors [1]. In order to identify the effects of the parameters in question, an n+p detector with doping profile (1e15 atoms/cm2) and low sheet resistance was processed. Before the processing of the device, Monte Carlo (MC) simulation methods were used to model the interaction between the electrons and the detector after the processing steps described above. This was employed to track the passage of bombarding electron particles through the detector taking into account possible interactions and decay processes. The simulations made use of "Standard" electromagnetic processes which Geant4 provides. With the aid of the program, we were able to investigate the energy deposit of electrons at different radiation energy per slice of 1 mm thick of the detectors at a given depth as well as compute a Linear Energy Transfer data (LET) that was then used in Taurus Medici to further analyze the detectors. To analyze the silicon bulk and the Si-SiO2 interface, we used some simple mobility models such as parallel field mobility model to account for carrier heating and velocity saturation effects. This was done by using analytic expressions for the drift velocity vd as a function of the electric field in the direction of current flow, E||, and defining μ(E||) = vd(E||)/E||. Other models used included Auger recombination model, Shockley-Read-Hall recombination model with fixed lifetimes as well as a concentration-dependent mobility model which involves the use of mobility tables to model the dependence of carrier mobility on impurity concentration. This research offers a significant improvement in electron detectors in applications like gas chromatography detection of trace amounts of chemical compounds in a sample. REFERENCES [1] O X Esebamen et al, 2011 JINST 6 P01001.doi: 10.1088/1748-0221/6/01/P01001 [2] H. Messel, D. Crawford. 1970 Pergamon Press.: Electron-Photon shower distribution [3] Synopsy, 2005. TCAD in Power Electronic.: TCAD News, USA, 1-4. http://www.synopsys.com [4] G.S. Sze, Fundamentals of Semiconductor Fabrication, John Wiley & Sons, 2004

Speaker: Omeime Xerviar Esebamen (Mid Sweden University)

58 Timepix background studies for double beta decay experiments

Timepix background studies for double beta decay experiments Joshy M. Jose for TGV and COBRA collaborations Institute of Experimental and Applied Physics, Czech Technical University in Prague The double beta decay (Beta-Beta) is very challenging subject of today’s physics. It can be used as a powerful tool to test neutrino properties (e.g. Dirac or Majorana type of neutrino) and lepton number conservation. There are various experimental approaches, e.g. GERDA [1], COBRA [2] (source=detector); SuperNEMO (tracking and calorimetric detector) [3] or CUORE (low temperature detector) [4]. In contrast to such big experiments devoted mainly to the Beta- Beta- decay, the search for 2-neutrino EC/EC decay (collaboration TGV [5]) is also important. This decay has not been observed yet in direct measurements (the only positive result is given by geochemical experiment [6] for 130Ba as (2.2 ± 0.5) x 10^21 years). All above mentioned general Beta- Beta- experiments are on the road towards setups with ~100 kg of isotope which could reach the sensitivity on the level of neutrino mass ~50 meV (depending on nuclear matrix element calculations). To be able to improve the experimental sensitivity there is a necessity to develop new experimental approach. One of the promising directions is the use of pixel detector techniques. Such R&D is running within the TGV (Si pixel detectors) and COBRA (CdTe pixel detectors) collaborations. We are performing intensive R&D towards the use of pixel detectors, TimePix [7] in the Beta-Beta (EC/EC) decay. The TimePix device, operated in time over threshold (TOT) mode, provides spectroscopic capabilities in each individual pixel. The main advantage of such detector is its ability to identify and reject background signals (e.g. tracks made by electrons, alpha particles, muons) and would efficiently recognize the signal of Beta-Beta decay processes (e.g. two X-rays with the energy of ~21 keV in two isolated pixels for 2-neutrino EC/EC) or two electron tracks with sum energy equal to Q beta-beta value for neutrinoless Beta-Beta). Two pixel detectors, Si (pixel size 55 x 55 um^2) and CdTe (pixel size 110 x 110 um^2) in surface laboratory as well as in underground laboratories (Modane underground Laboratory, LSM; Gran Sasso underground laboratory, LNGS) were tested from the point of view of intrinsic background. We had presented the idea of silicon pixel telescope (SPT) based on stacked silicon pixel detectors and initial background study results at the iWoRID2010 conference [8]. Final aim in both research areas (TGV, COBRA) is to build a multi-detector system based on the TimePix detectors working in coincidence mode. The quad detector should be used to increase the detector area in the case of SPT. For the purpose of COBRA the detector thickness should be optimized to maximize the amount of investigated isotopes. The first prototype of coincidence apparatus of two pixel detectors (face-to-face arrangement) has been constructed and tested. The results of long term background measurements (performed in LSM with the Si TimePix device and in LNGS with CdTe TimePix device) will be presented, as well as the results of test with coincidence apparatus. Also future plans with hardware developments will be presented. [1] Abt I. et al., Preprint hep-ex/0404039(2004). [2] Zuber K., AIP Conference Proceedings 1180 (2009) 145. [3] Chauveau E., AIP Conference Proceedings 1180 (2009) 26. [4] Arnaboldi C. et al., Phys. Lett. B584 (2004) 212-213. [5] N. Rukhadze et al., Nucl. Phys. A 852 (2011) 197-206. [6] A.P. Meshik et al., Phys. Rev. C 64 (2001) 035205. [7] X. Llopart et al., Nucl. Inst. Meth. A581 (2007) 485-494. [8] P. Cermak et al., JINST 6 (2011), C01057.

Speaker: Mr Joshy M. Jose (Institute of applied and experimental physics)

59 Trial electrode topology of a radiation detector: Design, modeling, semi-insulating GaAs technology and performance testing

The paper is devoted to design, numerical modeling, fabrication and evaluation of a detector with the new electrodes topology: standard sandwich-like two electrode detector is complemented by an additional electrode surrounding the small circular anode Schottky contact. It is shown that the detection efficiency of such detector with connected bottom and surface electrode increases 2-4 times for 5 keV photons while the dc leakage current changes negligible and it is very low. Hence the detector could operate at room temperature with good spectrometric performance. If all electrodes use Schottky barrier metallization, the detector could operates also in opposite polarity: negatively biased bottom contact connected with the surface additional electrode. In such case the detection efficiency for 5 keV photons increased even more, 3-6 times comparing to the standard two electrode configuration. In the former case, however, the leakage current is higher due to larger area of the bottom, cathode contact. Hence such detector operation needs lowered temperature using Peltier cooler. Moreover, the technology is more complicated by both-sided photolithography if the bottom full area contact is replaced by a contact with the defined area. The idea is applied and verified the semi-insulating GaAs material. I-V characteristis and pulse height spectra of the 241-Am are demonstrated at room as well as at lowered temperature down to -50 degrees Celsius. The detection efficiency of the 55-Fe is evaluated for different electrode connections. Preliminary results shows reverse current 1E-10 A at 295 K and -200 V (single cathode) or at -100 V (cathode connected with the additional surface electrode). The breakdown voltage exceeds -700 V. The energy resolution and the detectable threshold is limitted by the noise of the used preamplifier (about 1.5 keV FWHM for GaAs). Hence usage of ultra low noise preamplifier for detection evaluation in soft X-ray region will be neccessary.

Speaker: Dr Zaťko Bohumír (Institute of Electrical Engineering, Slovak Academy of Sciences, Bratislava, Slovakia)

60 Investigation of the crystallographic and detection properties of the CdTe at the ANKA synchrotron light source

Investigation of the crystallographic and detection properties of the CdTe at the ANKA synchrotron light source A. Cecilia, E. Hamann, C. Haas, D. Greiffenberg, A. Danilewsky, D. Haenschke, A. Fauler, A. Zwerger, R. Simon, T. Baumbach, M. Fiederle CdTe is widely used as room temperature detector for - and X-ray detection due to its high atomic number Z (48 and 52 for Cd and Te, respectively) and high density (5.86 g/cm3) which determine high absorption efficiency up to 100 keV for thicknesses above 1 mm [1]. The improvement of the material quality over the last years showed the good performance of CdTe pixel detectors. However, there are still some material issues to be investigated such as the presence of Te inclusions and small inhomogeneities. In addition, when CdTe detectors are illuminated with very high X-ray photon fluxes they experience a degradation effect [2]. In this work we have investigated semiconducting CdTe as pixelated sensor by using some of the available methods at the ANKA synchrotron facility (KIT, Karlsruhe). By combining white beam topography with X-ray diffraction and X-ray fluorescence methods we have characterised the crystallographic properties of the material. The topography results demonstrated the presence of several orientation contrast features that could be assigned to small angle grain boundaries. Those structures are disseminated in whole area of the investigated crystal and they form a network of dislocations inside the CdTe crystal. By means of the X-ray diffraction measurements we have estimated a grain boundary tilting angle around 0.01°. In view of the possible applications of CdTe at synchrotron facilities, the detector was illuminated with a varying X-ray flux between 1.2 x 106 ph/mm2s and 1.5 x 1010 ph/mm2s than can be expected at synchrotron facilities. The investigated CdTe sensors were processed at the Freiburg Material Research Centre (FMF) starting from a 3 inch CdTe wafer that was delivered from the Acrorad Japanese Company. One is a CdTe detector with M-p-n diode structure. The M layer is the Platinum contact; p is the slightly p-doped CdTe crystal and n is the electrode layer that connects the metallised area of the crystal to the readout electronic. The other detector is a quasi-ohmic CdTe sensor with Platinum electrodes on both sides. References [1] A. Zwerger, A. Fauler, M. Fiederle, “Medipix2: Processing and measurements of GaAs pixel detectors”, Nucl. Instr. And Meth. A, No. 576, p. 23-26 (2007). [2] D. S. Bale, C. Szeles, “Nature of polarisation in wide-bandgap semiconductor detectors under high-flux irradiation: application to semi-insulating Cd1-xZnxTe”, Phys. Review B 77, 035205 (2008).

Speaker: Mrs angelica cecilia (KIT (Karlsruhe, Germany))

Slides angelica.cecilia_iworid2011.ppt

19:00 Boat trip on Lake Zurich

Boat trip on lake Zurich

61 uhsdifaöuü

Slides Aufgabenerfassung.xlsx

Tuesday, 5 July

Front-end Electronics and Readout I: 3 contributions

Convener: Dr Jan Lammert Visschers (Nikhef Amsterdam, The Netherlands)

62 Radiation-Hardened and Radiation-Sensitive Single-Photon Imagers

Thanks to recent advances in the field of solid-state photon counters and single-photon imagers, there has been an increasing interest in studying the effects of long- and short-term radiation onto these detectors. In this talk we describe CMOS image sensors capable of detecting single-photon radiation at visible, ultraviolet, and near infrared wavelengths in hostile environments, such as high B-fields and intense gamma ray exposure. We focus on the architectures and the techniques that make these devices possible as well as their limitations and their applicability in disparate fields, such as high energy physics, biology, medicine, and entertainment.

Speaker: Mr Matthew Fishburn (Delft University of Technology)

Slides fishburn-iWoRID.ppt

Video animation avalanche.mp4

63 Detector and Electronics R&D for picosecond resolution, single photon detection and imaging

Photek, in collaboration with the University of Leicester space research centre, are pursuing a number of R&D projects aimed at developing systems for detection of single photon events with time resolution of the order of 10 ps. This involves the development of new detectors and accompanying electronics, utilising the HPTDC and NINO chips developed at CERN. An overview of R&D efforts will be presented, including results from a new multi-anode detector, jitter measurements on MCP-PMTs and current development progress on a benchtop HPTDC module.

Speaker: Dr James Milnes (Photek Ltd)

Slides Detector_&_Electronics_R&D.pptx

64 A Multi-Mode Hybrid Pixel Detector ASIC for Dosimetry and General Radiation Detection

Present-day dosimeters based on single diode implementations typically require strict presumptions regarding the radiation type and energy, have limited dynamic range, and tend to provide non-linear responses to energies within the ranges typical to occupational radiation environments. Moreover, the ability of the detector to resolve low energy photons is limited by the noise of the electronics. Hybrid pixel detectors provide a potential solution to these limitations. By segmenting the active area into many small channels, the probability of multiple radiation events simultaneously impinging on a single channel is greatly reduced, thereby allowing the front-end electronics to complete the processing of a single event before the arrival of the next event. Consequently, because the detector can process and provide energy information on discrete events, the linearity of the detector’s response is very high. As the electronics noise is a function of the input capacitance from the detector, the segmentation also lowers the detector’s noise-floor, thereby allowing a clean detection of low energy photons. In this work, we present a hybrid pixel detector ASIC with three programmable modes of operation: dosimetry mode, single photon counting mode, and energy integration mode. The ASIC comprises a matrix of 16 by 16 (256 total) square pixels of 220 μm pitch, providing 12.4 mm2 of segmented active area. Each pixel can be configured to operate in one of the three measurement modes, with programmable-depth counters and shift registers to tailor the data word size and optimise the readout frame-rate in a given mode. The individual energies of impinging photons are determined through programmable analogue energy threshold discrimination, time-over-threshold measurement, or a combination thereof. Furthermore, the dosimetry mode contains 16 digital energy thresholds and automatically sorts data into 16 corresponding energy bin registers. The emphasis of this paper will be on the implementation of the shared electronics which enable the three modes within the same pixel area. A discussion on the initial electrical measurements of the prototype ASIC will also be presented.

Speaker: Winnie Wong (CERN)

Slides IWORID2011_Winnie.ppt

65 PImMS – An event-triggered time-stamping CMOS Image Sensor for Mass Spectrometry

The PImMS Sensor is an event triggered time-stamp storing CMOS image sensor for Time Of Flight (TOF) Mass Spectrometry. The device features a 72 by 72 pixel array with better than 50 ns timing resolution and 4 registers per pixel for 12-bit time-stamp storage. The multiple registers and high temporal resolution allow the detection of all incident mass peaks within each measurement period without the need to gate or exclude certain masses, increasing throughput. By combining traditional TOF Mass Spectrometry techniques with a 2D pixelated detector it is possible to extract addition information about the spatial position or the velocity of the ions when generated. The sensor has been designed and fabricated in the INMAPS 0.18 µm process which allows for the inclusion of complex full CMOS electronic circuits within the pixel without significantly affecting the detection efficiency of the monolithic sensor architecture. We will present an overview of the device design and features, measurements of device performance and results from the Mass Spectrometry application. Further applications for the sensor will also be described.

Speaker: Mr Andy Clark (STFC Rutherford Appleton Laboratory)

Slides AClark_IWoRID2011_PImMS.ppt

Poster Mini Talks IV

Convener: Dr Jan Lammert Visschers (Nikhef Amsterdam, The Netherlands)

66 Analog signal from common electrode of pixelated detector for triggering and spectroscopy

The Medipix/Timepix device consists of a semiconductor detector chip (usually silicon) bonded to a readout chip. The detector chip is equipped with a single common backside electrode and a front side matrix of electrodes (256 x 256 square pixels with pitch of 55 µm) bump bonded to Medipix/Timepix read-out chip. A significant advantage of these pixel detectors is the possibility of direct observation of traces of single particles. In many cases, however, these particles are accompanied with background of other unwanted particles overlapping traces of the desired radiation. The selectivity of the detector can be increased using a self-triggering approach especially if combined with an external trigger from other detecting devices such as ionization chambers, scintillating or semiconductor detectors. Unfortunately the Medipix/Timepix devices are not equipped with self-trigger feature. A solution which is proposed in this contribution uses the analog signal from the common electrode of the pixelated sensor. This signal called back-side-pulse is amplified by a charge sensitive preamplifier and, after shaping, it can be used as fast trigger and as independent spectroscopic signal. The stability and energy resolution of this analog signal is, however, strongly affected by interference from the digital read-out interface. In this contribution we present the solutions of suppression of electromagnetic. The result allows to select a particular particle in a mixed radiation field. The technique is demonstrated on measurements with heavy charged particles from radioactive α-sources 241Am, 239Pu as well as spontaneous and neutron induced fission sources 252Cf and 235U, respectively.

Speaker: Mr Michal Platkevic (IEAP CTU in Prague)

Slides minitalk.pptx

67 CMOS peak detect and hold using diode connected MOSFET

Peak detectors (peak-detect-and-hold circuits, PDHs) are a key element in nuclear electronics signal processing and have been incorporated as a fully integrated block in several front-end readout chips. The passive type PDH using diode has very simple structure and high energy efficiency. Though the virtues of a diode PDH, it is not easily employed because of the loss and the distortion of a signal due to its potential barrier. On the other hands, in CMOS designs, the active type PDH uses an MOS current source as the rectifying element inside the feedback loop of a high-gain amplifier. This type of PDH is recently widely used by virtue of the accuracy. However, the active type CMOS PDH has complicated structure and heavy power consumption compared with the passive type PDH. We propose the passive PDH using diode connected MOSFET and overcome the loss and the distortion of the signal occurred by threshold voltage of MOSFET similar with the diode potential barrier. * corresponding author e-mail: ychoi@cau.ac.kr

Speaker: Mr IN-IL JUNG (CHUNG-ANG UNIVERSITY)

Slides MINI_talk_B_.pptx

68 Development of a Versatile Readout System for Medipix2 Pixel Detectors in Synchrotron Radiation Applications

Hybrid Pixel Array Detectors (HPAD) are revolutionizing the field of photon detection at synchrotron storage ring and free-electron laser light sources. Excellent detection quantum efficiency, high throughput and noise performance are major improvements over current detectors based on charge coupled device (CCD) cameras. Examples of HPAD detectors are Pilatus, Medipix and XPAD. The German-Russian collaboration Galapad developes Medipix pixel detectors for the use in synchrotron applications. The chosen GaAs sensors realize higher efficiency resulting in the need for fast data processing electronics. We are implementing a flexible data acquisition system utilizing the Virtex-6 FPGA ML605 Evaluation Kit. It allows the communication via the USB bridge, the gigabit Ethernet or the high data rate PCI-Express. The sensitive surface of the multichip system, 3x2 high-Z semiconductor detectors, is read-out serially at a clock speed of 150 MHz with an initial frame rate of 30 frames/s The prototype comprises the complete data acquisition system to provide a compact camera. It is capable of integrating existing hardware and the software package “Pixelman” and is compatible with the Medipix2 family, including TimePix and Medipix3. The versatility of this system makes it suitable for a range of applications. The sensors will be tested using a variety of materials (e.g. Si, CdTe and GaAs). The performance of the system will be evaluated with various radiation sources like X-ray tubes and synchrotron radiation.

Speaker: Dr Andrea S, Brogna (Karlsruher Institut für Technologie)

Slides iword2011.odp

69 FITPix Data Preprocessing Pipeline for the Timepix Single Particle Pixel Detector

The semiconductor pixel detector Timepix contains an array of 256 × 256 square pixels with pitch of 55 µm. The single quantum counting detector Timepix can provide also energy or time information in each pixel. This device is a powerful tool for radiation imaging and ionizing particle tracking. The Timepix device can be read-out via serial or parallel interface enabling speed of 100 fps or 3000 fps respectively. The device can be connected to a PC via USB2.0 based interface FITPix which currently supports the serial output of Timepix reaching speed of 90 fps. The FITPix features adjustable clock frequency and hardware triggering which is a useful tool for the synchronized operation of multiple devices. The FITPix interface can handle up to 16 detectors in the daisy chain. The complete system of FITPix interface and Timepix detector is controlled from PC by Pixelman software package. This paper reports on the pipeline structure which has been newly implemented into the new version of FITPix. This version supports also the parallel Timepix read-out. The pipeline architecture brings possibility of data preprocessing directly in hardware. The first pipeline stage converts the raw Timepix data into form of matrix or stream of pixel values. Another stage performs further data processing such as event thresholding and data compression. This way a complex data processing currently performed by Pixelman in PC is significantly reduced. The described architecture together with the parallel read-out increases data throughput reaching higher frame-rate and reducing the dead time. The data compression performed directly in hardware is significant especially for sparse data from particle tracking applications. The frame size is compressed typically by factor of 10-100. This work was carried out within the CERN Medipix Collaboration.

Speaker: Mr Vaclav Kraus (IEAP CTU in Prague, University of West Bohemia in Pilsen)

Slides Presentation for mini talk.

70 Influence of electromagnetic interference on the analog part of hybrid pixel detectors

The analog signal from the sensor of hybrid pixel detectors is hindered by electro-magnetic interference. A systematic diagnostics of induced and common electro-magnetic coupling between the analog part and digital part of these devices is required. An influence of electro-magnetic interference on a detector precision was observed on the setup of a pixel particle detector and a read-out interface. The tested system was composed of a Medipix or Timepix pixel detector connected to a FITPIX readout. To get relevant information about electro-magnetic interference several measurements were undertaken. We focused on measurement of external as well as internal interference. We evaluated the influence of both sources of electro-magnetic interference to the noise recorded by pixels. We measured local spatial intensity distribution and frequency spectrum of electro-magnetic field originating inside of the readout chip during its own operation. In context of this test we exposed detector chip to the locally generated artificial electro-magnetic field evaluating its sensitivity to induced interference. Consequently, whole setup of detector and read-out interface was exposed to a distant source of electro-magnetic radiation, during which we tested efficiency of electro-magnetic shielding of various arrangements. In next tests coupling over power supply lines was measured. Primarily, a noise generated by own detector operation was determined. Secondarily, the detector sensitivity to deliberately induced noise was evaluated. By means of these tests weak points of the setup sensitive to the intrusion of electro-magnetic interference are revealed. When locations of susceptible places are identified a proper methods can be applied to increase immunity of the detector setup against the electro-magnetic interference. Gained experiences are planed to be used in development of EMI shielded version of FITPIX interface immune to electro-magnetic interference.

Speaker: Mr Michael Holik (IEAP CTU in Prague)

Slides minitalkb_-_holik_-_influence_of_emi.ppt

71 Modular High Bandwidth Data Acquisition System with Gigabit and 10 Gigabit Ethernet Uplinks

The data acquisition (DAQ) system was designed to capture incoming data at a rate of 25.2 Gbit/s per half-module and send them to a storage system over standard Ethernet connections. It consists mainly of a customizable front-end board (FEB) for data preprocessing and a back-end board for buffering up to 8 Gbyte of data before transmitting them to the storage system. Small form-factor pluggable (SFP) and SFP+ modules allow the use of optical fibers or copper cables covering a data rate from 10 Mbit to 10 Gbit. A Linux operating system running on a PowerPC Processor inside the FPGA is used for handling slow control and system monitoring tasks as well as in the field upgrades of all programmable system components over the Ethernet connection. The system is now in the commissioning phase to read out the EIGER X-ray detection chip developed at the Paul Scherrer Institut (PSI). With adaption of the FEB it is possible to use this DAQ system for many other tasks.

Speaker: Gerd Theidel (PSI)

Slides ID225_PSI_Schmid_Theidel_iWoRiD13_2011.ppt

72 Single Photon Counting based on the Fast-Digitizing, High-Resolution WaveDREAM Data Acquisition System

Many experiments and applications demand high-resolution, fast waveform digitizing. The use of a switched capacitor array (SCA), as employed by the DRS4 Application Specific Integrated Circuit (ASIC), offers significant cost and power reduction compared to a traditional flash analog-to-digital converter (ADC). The WaveDREAM data acquisition system, based on the DRS4 ASIC, allows continuous digitization of analog signals at 120 Mega-samples per second (MSPS) with the possibility to sample a region of interest at a rate of up to 5 Giga-samples per second (GSPS). Since a low-resolution (120 MSPS) version of the input signal is continuously presented to the digital domain, arbitrarily complex trigger logic can be implemented in a field-programmable gate array (FPGA), while retaining excellent timing resolution in the region of interest. The signal-to-noise ratio (SNR) of the system is measured to be 9.3 bit for the 120 MSPS signal and 9.6 bit for the DRS4 readout signal. A Gigabit Ethernet link provides high-speed connectivity from the DAQ board to the backend system. Built-in board-to-board communication and the modular design of the system offer great scalability and flexibility with respect to the number of supported data channels. Timing resolution is of the order of one nanosecond across the entire system, while being significantly better within one DRS4 ASIC. The excellent time synchronization, high channel density, and low power consumption make WaveDREAM well suited for applications in the field of radiation imaging, where a high number of channels and good timing resolution is required. This work presents the WaveDREAM system and discusses potential applications, including single photon counting, pulse shape discrimination, time-of-flight (TOF) measurements using constant fraction discriminatior (CFD), and many more. Measurement results are shown for single photon counting, and implications for future versions of the DAQ system are discussed.

Speaker: Mr Hannes Friederich (ETH Zurich)

Slides slides (Protected)

73 Optimalization of spectroscopic response of Timepix detector

The so called Time over Threshold mode of the semiconductor pixel detector Timepix allows direct measurement of the deposited energy in each pixel. The Timepix is thus well suited for measurements where the precise position and energetic information are required. The Time over Threshold measurements requires energetic calibration of each pixel. The energetic calibration procedure of the pixels for a given threshold value is well known and published. The wide dynamic range (in energy from keV to MeV) which can be registered in each pixel in different applications puts high demands on the preamplifiers and analog circuits of the detector chip. The preamplifier and analog circuit characteristic of the Timepix are controlled and can be adjusted by a set of detector parameters. This systematic response of the detector with respect to the large number of parameters was not properly studied before. In this contribution we presents the optimalization of the spectroscopic performance of Timepix detector by finding the best settings of detector parameters with respect to very different application areas, such as X-ray imaging, X-ray fluorescence or heavy ion measurements, respectively.

Speaker: Mr Martin Kroupa (IEAP CTU in Prague)

Slides kroupa_iworid_2011_minitalk.ppt

74 Effect of Photodiode Structures on the Dark Current of CMOS Active Pixel Sensor for X-ray Imaging

In this study, we designed and fabricated active pixel sensors with various photodiode structures using 0.18 μm 1Poly/4Metal CMOS process. All photodiodes have 50 μm pitch for X-ray imaging and the same pixel structure, 3-transistor active pixel. First of all, we considered three basic photodiode structures, n-well/p-epi, n+/p-epi and p+/n-well/p-epi, available in the standard CMOS process. A trade-off between sensitivity and dark current for the specific wavelength emitted from the CsI(Tl) scintillator was measured. Moreover, we investigated the effect of shallow trench isolation (STI) on dark current. Since the used process provides flexibility to design the photodiode, we could utilize STI blocked n+ and n-well regions and easily control the distance between photodiode junctions and STI regions. Finally, the dependence of dark current on the photodiode shape as well as the number of contacts is examined. In order to obtain precise and analytical results, the test pixels were connected to off-chip 16-bit analog-to-digital converters (ADCs) and the data processing was performed through the graphic user interface (GUI) program using Labview and Matlab.

Speaker: Mr Jun Hyung Bae (KAIST)

75 Noise analysis of CMOS readout circuits

Equivalent noise charge (ENC) is useful method for indicating total noise of detection system [1]. Here, the quantity of ENC depends on aspect ratio of a transistor which places on the input of the preamplifier. Analyzed ENC is use to minimize system noise in designing CMOS readout circuits in the gamma-ray detection system. The analysis in [1] is quietly effective to design CMOS readout circuits, however, the overdrive voltage and the bias current of the input transistor of preamplifier is missed. Theses parameters are important to satisfy saturation condition of the readout circuits and also important to achieve a linearity of readout circuit. As discussing these parameters and analyzing the influence of them, we propose the more effective method of designing readout circuits. In addition, we suggest the need of suppressing flicker noise by showing the difference of noise analysis between 0.35 μm and 0.18 μm CMOS technology. * corresponding author e-mail: ychoi@cau.ac.kr References 1. Arturo TAURO, C.Marzoccar. “A CMOS 0.35μm Analog Front-End Electronics for Gamma Ray Medical Imaging”, POLITECNICO DI, 2006

Speaker: Mr IN-IL JUNG (CHUNG-ANG UNIVERSITY)

Slides MINI_talk_A.pptx

10:20 Coffee Break

Detector Systems I: 4 contributions

Convener: Prof. Valeria Rosso (Physics Department and INFN, Pisa, Italy)

76 From single photon counting to tracking detectors

Recent advances in semiconductor technology allow constructing highly efficient and low noise pixel detectors of ionizing radiation. Steadily improving performance of front end electronics enables fast digital signal processing in each pixel which enables to register more complete information about each detected quantum (energy, time, number of particles). All these features improve and extend the applicability of pixel technology in different fields. In most imaging application the pixel detectors are operated in single particle counting mode. In this mode the signal generated by the particle is compared with a certain preselected energy threshold to remove noise and, if higher, it is counted in a digital counter. Such approach provides low noise, energy discrimination and absolutely linear image accumulation. Resulting images have extremely high dynamic range and virtually unlimited contrast which plays an important role in imaging of low contrast objects such as soft tissue structures. Pixel detectors can be operated also in the so called tracking mode with reduced exposure time having only few particle traces in each frame. The shapes of such traces are characteristic for different particle types. Some pixel detector such as Timepix can measure also the arrival time or energy deposited by the particle in each pixel. Analyzing the shapes of the recorded traces it is possible to collect more information about the passing radiation. For instance it is possible to suppress undesired background caused by particles with differently shaped traces, to improve spatial resolution or to create full energy spectra in each pixel. Using coincident techniques based on time stamping it is possible to derive also other radiation properties such as polarization of X-rays, identification of secondary particles and nuclear reaction or decay products. Radiation imaging methods can be based or enhanced by particle tracking principles. A few examples will be given such as fully spectroscopic X-ray transmission imaging, neutron and proton radiography with very high spatial resolution and imaging based on ion scattering. A brief view into the future of pixel detectors and their applications including also spectroscopy, tracking and dosimetry will be given too. Special attention will be paid to the problem of detector segmentation in context of the charge sharing effect. This work is carried out in frame of the Medipix Collaboration.

Speaker: Dr Jan Jakubek (IEAP, CTU in Prague)

Slides 01-Jakubek_-_IWORID2011_-_Zurich.ppt

77 Development of LAMBDA: Large Area Medipix-Based Detector Array

The Medipix3 photon counting readout chip has a range of features – small pixel size, high readout rate and inter-pixel communication – which make it attractive for X-ray scattering and imaging at synchrotrons. DESY have produced a prototype large-area detector module that can carry a 6 by 2 array of Medipix3 chips (1536 by 512 pixels), which can be used with a single large silicon sensor (85mm by 28mm) or two “hexa” high-Z sensors. The detector head is designed to be tilable and compatible with low temperatures, and will allow high speed parallel readout of the Medipix3 chips. It consists of a LTCC ceramic board, on which the sensor assembly is mounted, and a secondary board for signal routing and voltage regulators. A prototype DAQ board using USB2 readout has also been produced. Medipix3 readout chips have been mounted on the detector head, and successfully configured and read out by the DAQ board. Currently, a higher-speed readout board using 10GBE links is being developed, and a set of large-area silicon sensors are in production. DESY are also collaborating with other institutes and companies to develop high-Z sensors for use with this module.

Speaker: Dr David Pennicard (DESY)

Slides Lambda_IWorid_presentation_v10.pdf Development of LAMBDA - Large Area Medipix Based Detector Array

78 Towards ps and fs diffraction with the XPAD detector

Short (ps) or ultra-short (fs) synchrotron X-ray pulses enable to probe the dynamics of photo-induced molecular states, collective movements in solids, or the course of chemical reactions. In so-called ‘pump-probe’ experiments, the system being studied is excited by a fs or ps laser pulse and probed after a certain delay by a pulse of synchrotron X-rays. This procedure must be repeated many times, in a stroboscopic way, to generate the necessary statistics for a reliable measurement. Experiments of this kind are already being carried out in synchrotron radiation centres, where the beam delivered is naturally pulsed thanks to the ‘bunch’ structure of the electron beam in the storage ring. Nevertheless, to perform time-resolved experiments, only the X-ray pulse immediately following the laser pulse should be counted. In SOLEIL’s‘eight-bunch’ mode for example, the counting of diffracted photons must be enabled for no longer than twice the bunch spacing, 2x147ns ~300 ns.The 2D detectors normally used in diffraction, CCD cameras or image plates cannot switch that quickly. This is the reason why the selection of the X-ray pulse to be measured is usually performed by a mechanical selector, or ‘chopper’. Unfortunately, choppers are limited to a maximum frequency of 1 kHz, cannot be fully frequency-tuned, and involve a complex mechanical design. In collaboration with the CCPM and the CRG D2AM beamline at ESRF, the Detector group of SOLEIL is developing a hybrid pixel detector: XPAD. The version 3.2 of this detector has been optimised to be able to count on a duration specified by the width of a logic gate, at any frequency. The rest of the time, the counting of photons is disabled. The feasibility of pump probe experiments with XPAD3.2 was proven on SOLEIL’s CRISTAL diffraction beamline, where a single chip was synchronized to one of the eight bunches circulating in the storage ring, at up to 100 kHz. A module consisting of 7 chips hybridized to a Si sensor (7×1.5 cm2) will be used this spring, to study the structural dynamics of molecular spin-crossover crystals induced by a laser pulse. The preliminary results, from the detector point of view, of this experiment will be presented. The full detector (8 modules, 56 chips, 7×12 cm2, Si sensor) will be available for pump probe experiments at SOLEIL by the end of this year.

Speaker: Dr Stephanie Hustache (Synchrotron SOLEIL)

Transparents IworidHustache.pdf IworidHustache.ppt

79 EIGER a new single photon counting detector for X Ray applications: performance of the chip.

EIGER is the next generation of single photon counting detector for synchrotron radiation designed by the PSI-SLS detector group. It features a pixel size of 75x75 μm2 and frame rates up to 22kHz. An array of 256x256 pixels fits on a 2cm x 2cm chip. The chip provides 4, 8 and 12 bit counting modes and practically an infinite dynamic range (32 bits) due to the continuous read/write and the summation of frames on the fly in firmware. Along with the first X Ray absorption images, the characterization and performance of the chip will be presented. The most important parameters i.e. energy calibration, noise, minimum energy threshold and rate capability were measured on a single chip system with an X Ray tube and at the SLS-PSI synchrotron. Trimming and irradiation studies will be discussed. Tests so far have shown that the EIGER system meets its specifications. A report on the status and plan for a full module (2x4 chips) and 4M pixel EIGER detector will also be given.

Speaker: Valeria Radicci (Paul Scherrer Institut)

Slides VRadicci_iworid2011.ppt

80 The GOTTHARD charge integrating readout detector: design and characterization

A charge integrating readout ASIC for silicon strip sensors has been developed at PSI in collaboration with DESY. The goal of the project is to provide a charge integrating readout system able to cope with the pulsed beam of XFEL machines and at the same time to retain the high dynamic range and single photon resolution performances typical of photon counting systems. The ASIC, designed in IBM 130nm CMOS technology, takes advantage of its three gain stages with automatic stage selection to achieve a dynamic range of 10000 12 keV photons and a noise better than 300 electrons (ENC). The 4 analog outputs of the ASIC, optimized for speed, allow frame rates in excess of 1MHz, without compromises on linearity and noise performances. This work will present the design features of the ASIC, and will report the characterization results of the chip prototypes (GOTTHARD 0.2-0.3) and of the final chip itself (GOTTHARD 1.0).

Speaker: Dr Aldo Mozzanica (Paul Scherrer Institut)

Slides mozzanica_iworid_2011.pdf

Poster Mini Talks V

Convener: Prof. Valeria Rosso (Physics Department and INFN, Pisa, Italy)

81 Measurement of distribution of fast neutrons produced in ion beam therapy with the 3D sensitive voxel detector

Ion beam therapy is a rapidly developing method for treatment of certain types of cancer. A main advantage of ions is that they deposit most of the energy at the end of their range according to the Bragg curve. Unfortunately, the ion beam often generates (by various mechanisms such as fragmentation) a substantial amount of secondary particles with longer range (protons and other light fragments, neutrons, gamma particles, X-rays and electrons). Thus, a certain fraction of dose is deposited by other than the primary ions outside of the planned volume. It is, therefore, very important to estimate and experimentally verify the distributions of these secondary particles. It is particularly difficult to measure the distribution of fast neutrons generated by ions in tissue. Fast neutrons are usually detected via their interaction (scattering) with hydrogen nuclei (proton). The proton recoiled by neutron can be subsequently detected by various sensors. The problem is that certain fraction of secondary particles consists of protons as well. Therefore, it is necessary to distinguish protons recoiled by neutrons from protons naturally present in the sample. In this work we present the experimental technique enabling the separation of fast neutrons from protons. The technique uses a 3D sensitive voxel detector composed of several layers of Timepix pixel detectors. These layers are interlaced with a hydrogen rich material (plastic) serving as a convertor of neutrons to recoiled protons. The device records the traces of all interacting radiation providing the timestamp and/or deposited energy for each single particle. A proton passing through the detector creates a trace in all layers, whereas a protons recoiled by neutron originates in the convertor inside of the structure creating a trace in the inner layers only. This way it is possible to distinguish the protons from neutrons with very high selectivity. An initial experimental study to register the outcoming neutron radiation was performed at the Heidelberg Ion Beam Therapy Center (HIT) in Germany using medical proton and carbon ion beams. This work is carried out in frame of the Medipix Collaboration.

Speaker: Dr Jan Jakubek (IEAP, CTU in Prague)

82 Application of Timepix in LWFA experiments: high flux single shot measurement of betatron radiation from x-rays to gamma-rays

Betatron radiation emitted by electrons accelerated in a laser plasma wakefield accelerator is a promising bright ultra-compact light source. The presence of the electromagnetic field of the laser in the accelerator can dramatically change the electron motion with an emission from soft-x-rays to gamma-rays. We studied the radiation properties in single-shot experiment using two different Timepix detectors, based on silicon and cadmium telluride respectively, to record the emitted betatron spectra. Compton side scattering technique has been used to extend the working range of Timepix both in maximum photon energy and flux.

Speaker: Ms silvia cipiccia (strathclyde university)

83 First steps towards small prototype gamma camera based on wavelength shifting fibers

We are studying and developing a gamma camera based on optical fibers coupled to both sides of inorganic scintillation crystals and using for the light readout highly sensitive photodetectors, namely silicon photomultipliers (SiPMs) and high efficiency multi-anode photomultiplier tubes (MaPMTs). The coupling of the fibers in orthogonal directions allows obtaining 2D position information, while the energy signal is provided by a PMT. The application of optical fibers combined with SiPMs as light sensors is likely to improve the spatial resolution to the 1-2 mm FWHM level, thus improving the sensitivity of scintigraphy techniques. A first prototype laboratory system has been developed using a custom-made 50×50×3 mm3 CsI(Na) crystal with embedded 1 mm Ø fibers and reading out the light from 12 of the fibers in each direction with a MaPMT. Proof-of-concept studies and results obtained with this system using Co-57 are presented. Larger prototype systems up to 12 × 12 cm2 are planned, using 1 mm2 SiPMs individually coupled to the fibers. Ongoing development and preliminary results of these prototypes will be presented.

Speaker: Mr Filipe Castro (Universidade de Aveiro)

Minutes Poster highlight slides (with animation)

Poster Poster

84 Micro-radiography of Biological Samples with Timepix

Micro-radiography is an imaging technique using X-rays in the studies of internal structures of objects. This fast and easy imaging tool is based on differential X-ray attenuation by various tissues and structures within the biological sample. The non-absorbed radiation is detected with a suitable detector and creates a radiographic image. In order to detect the differential properties of X-rays passing through structures sample of various compositions, an adequate high-quality imaging detector is needed. We describe the recently developed radiographic apparatus, equipped with Timepix semiconductor pixel detector. The detector is used as an imager that counts individual photons of ionizing radiation, emitted by an X-ray tube FeinFocus with tungsten, copper or molybdenum anode. Thanks to the wide dynamic range, time over threshold mode - counter is used as Wilkinson type ADC allowing direct energy measurement in each pixel of Timepix detector and its high spatial resolution better than 1µm, the setup is particularly suitable for radiographic imaging of small biological samples. We are able to visualize the internal biological processes and also to resolve the details of insects (morphology) using different anodes. Our images and spectra of anodes are shown in the poster section.

Speaker: Mr Jiri Dammer (IEAP CTU in Prague)

85 Design and image-quality performance of high resolution CMOS-based X-ray imaging detectors for digital mammography

A variety of digital mammography detectors are currently used in the early diagnosis of a breast tumor and cancer. Direct conversion method with amorphous selenium and indirect detection type such as amorphous silicon (a-Si) flat panel arrays (TFT), CCDs with scintillation materials have been widely employed as an X-ray image sensor in clinical use for several years. More recently, CMOS (complementary metal-oxide semiconductor) imaging detectors in conjunction with a scintillation screen have been appeared as an attractive candidate due to relatively low fabrication cost, low power consumption, compactness and high frame rate in many scientific and medical applications. Therefore, we tried to investigate the potential use of a scintillator-based CMOS APS (active pixel sensor) for high resolution digital mammography. In this work, two type scintillation materials such as Gd2O2S:Tb and CsI:Tl with a columnar structure were used as a conversion material of an incident X-ray into visible lights. The 100μm-thick screen with Gd2O2S:Tb particle in acrylic binder was fabricated through screen printing method and 150μm-thick CsI:Tl screen with a needle structure was fabricated by thermal evaporation process. The X-ray converter screens were fabricated onto a white TiO2 reflective layer coated glass substrate for low-dose X-ray mammographic imaging. And also, the CMOS flat panel imager with 25x50mm2 active area and 48μm pixel pitch was used for high resolution imaging acquisition. The imaging characterization of the used X-ray detector was measured and analyzed in terms of linearity about incident X-ray dose, modulation transfer function(MTF), noise-power spectrum(NPS) and detective quantum efficiency(DQE) using a W/Al mammographic X-ray source with various energies of 25-50kVp.

Speaker: Dr Bo Kyung Cha (KERI(Korea Electrotechnology Research Institute))

86 Phase Contrast Imaging at Classical and Compact Synchrotron Light Sources for Medical Applications

Phase contrast imaging shows promising improvements over absorption contrast imaging, especially when it comes to the discrimination of soft tissues. Grating interferometer based phase contrast imaging (GIBP) in particular allows the recording of the classical absorption signal as well as the complementary phase and dark field signals, making it a powerful diagnostic tool in medical applications. While being compatible with classical X-ray sources, GIBP suffers from the large energy spectrum of emitted photons. The photon energy dispersion indeed leads to a washing out of the Talbot carpet which serves as a basis for the phase signal recording (Figure 1 & 2) and finally to a decrease of the signal to noise ratio. One way of solving this problem while remaining compatible with bedside applications is the use of miniature synchrotron light sources such as the compact light source (CLS - Lyncean Tech) which provide a high brilliance monochromatic source of photons with energies up to 35 keV. Another approach is the use of X-ray imaging detectors with energy discrimination capabilities such as the Medipix 3 readout chip combined to a high Z material sensor. In the frame of the future MAP2 project which encompasses the installation and use of a Compact Light Source “BRIX” in the Munich area to perform advanced preclinical studies, and in order to explore the domain of spectral phase contrast imaging, a dedicated detector development program is planned. The planned detector is based on the Medipix 3 readout chip bump bonded to a high Z material sensors and will a) offer the speed and noise performance needed to perform the various BRIX based experiments, and b) allow to explore the domain of spectral phase contrast imaging thanks to the capabilities of Medipix 3 chip spectroscopic mode. This proposed poster offers to detail the use of the detector in the phase contrast based MAP2 proposed applications.

Speaker: Mr Franz Michael Epple (TU Munich, Biomedical Physics E17)

87 Performance Measurements of a Depth-Encoding TraPET Detector Module

The new method to correct a parallax error and the loss of coincidence counts caused by the gap between modules was developed for a small animal PET. We proposed the TraPET scanner composed of 6 dual-layer phoswich detector modules. Each detector module consists of a 5.0 mm-thick trapezoidal-shaped monolithic LSO with a front face of 44.0 x 44.0 mm2 and a back face of 50.0 x 50.0 mm2 and a 25 x 25 array of GSO crystals with a size of 2.0 x 2.0 x 10.0 mm3. The layer of interaction is distinguished by the pulse shape discrimination method. One detector module was built and its performance was evaluated in terms of spatial resolution, sensitivity and the accuracy of the layer identification. The dual-layer crystals were optically coupled to a Hamamatsu H8500 position-sensitive PMT and a resistive charge divider was used to multiplex 64-channel anode outputs into 4-channel position signals. The 4 signals were being sampled continuously by 14-bit ADC at a sampling rate of 105 MHz and the pulse shape discrimination algorithm was achieved through FPGA programming. The detector module was irradiated with a Na-22 point source from the side of the crystals to obtain flood images of each layer and two layers were clearly identified, thus verifying the DOI capability. In this paper, TraPET detector proved to be a reliable design for correcting the parallax error and improving the sensitivity simultaneously in the small animal PET.

Speaker: Mr Cheol Ha Baek (Yonsei university)

88 Development of a Large-Angle Pinhole Gamma Camera with Depth-of-Interaction Capability for Small Animal Imaging

The large-angle gamma camera was developed for imaging small animal models used in medical and biological research. In the simulation study, a large field of view (FOV) of this system provides higher sensitivity than typical pinhole gamma cameras by reducing the distance between the pinhole and the object. However, this gamma camera suffers from the degradation of the spatial resolution at the periphery region due to parallax error by obliquely incident photons. We proposed the new method to measure the depth of interaction (DOI) using three layers of monolithic scintillators to reduce the parallax error. The detector module consists of three layers of monolithic CsI(Tl) crystals with dimensions of 50.0ｘ50.0ｘ2.0 mm3, a Hamamatsu H8500 PSPMT and a large-angle pinhole collimator with an acceptance angle of 120˚. The 3-dimensional event positions were determined by the maximum-likelihood position-estimation (MLPE) algorithm and the pre-generated look up table (LUT). Spatial resolution of the Tc-99m point source was measured as 3.10, 3.81 and 4.14 mm with the conventional method (Anger logic) and 2.39, 2.69 and 2.47 mm with DOI information at the center, 10 cm and 15 cm off-center of the FOV, respectively. We proved that high sensitivity can be achieved without degradation of spatial resolution by using a large-angle pinhole gamma camera which can be used as small animal imaging. Keywords: Large-pinhole gamma camera, depth of interaction(DOI), maximum-likelihood position- estimation (MLPE)

Speaker: Mr Cheol-Ha Baek (Department of Radiological Science, College of Health Science, Yonsei University)

89 Real-time X-ray microradiographic imaging and image correlation for local strain mapping in single trabecula under mechanical load

X-ray microradiography was employed to quantify the strains in loaded human trabecula. Samples of isolated trabeculae (n=6) from human proximal femur were extracted and glued in a loading machine specially designed and manufactured for the purpose. The samples were then tested in tension (n=3) and three-point bending test (n=3) until complete fracture of the specimen. To assess the deformation in the very small samples (thickness 0.1 mm, length 1-2mm) a real-time microradiography in conjunction with digital image correlation (DIC) has been employed. Loaded samples were illuminated continuously by X-rays (Hamamatsu L8601-01 with 5μm spot) during the test. Radiograms were acquired using 0.25s exposure time with hybrid single-photon counting silicon pixel detector Medipix2 (matrix 256×256 sq. pixels of 55 μm pitch). The distance between the source and detector was kept small to ensure radiograms of good quality in such a small time interval. Design of the experimental loading device enables for precise control of the applied displacement which is important for the post-yield behaviour assessment of trabeculae. Unlimited dynamic range, high sensitivity and high contrast of the Medipix2 enables measuring even very small strains with DIC. Tested experimental setup enables to combine micromechanical testing of the basic building block of trabecular bone with time-lapse X-ray radiography to measure the strains and to assess the mechanical properties of single human trabecula and capture the softening curve with sufficient precision.

Speaker: Dr Ondrej Jirousek (Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic)

Slides doktor_jirousek_et_al.pdf

90 Test of different pixel detectors for laser-driven accelerated particle beams

Laser driven accelerated (LDA) particle beams have due to the unique acceleration process very special properties. In particular they are created in ultra-short bunches of high intensity typically up to 10^9 particles/cm²/ns. Characterization of these beams is very limited with conventional particle detectors especially with non-electronic detectors like radiochromic films, imaging plates or nuclear track detectors which are still broadly used at present. Moreover, all these detectors give only offline information about the particle pulse position and intensity as they require minutes to hours to be processed, calling for a new highly sensitive online device. Therefore, we are using pixel detectors for real time detection of LDA ion pulses. As each pixel represents a small detector unit in itself, only a small fraction of the whole beam will be detected by it and so problems due to detector saturation might be overcome by this new approach. Besides beam flux monitoring with high spatial and temporal resolution, additional knowledge about beam energy is also advantageous. Tests have been performed at the Munich 14MV Tandem accelerator in an 8-20 MeV proton beam in dc and pulsed irradiation mode, the latter simulating LDA-like ns ion pulses. For detection tests we chose the position-sensitive quantum-counting semiconductor pixel detector Timepix which also provides per-pixel energy- or time-sensitivity. Additionally other types of commercially available pixel detectors are being evaluated such as the RadEye1, a large area (25 x 50 mm²) CMOS image sensor based on a photodiode array in a matrix of 512 x 1024 pixels with 48 micron pixel pitch. All of these devices are able to resolve individual particles of the beam with high spatial- and energy-resolution down to the level of µm and tens of keV, respectively. Various beam delivering parameters of the accelerator were thus evaluated and verified. The different readout modes of the Timepix detector which is operated with an integrated USB-based readout interface allow online visualization of single and time-integrated events. Therefore Timepix offers the greatest potential in analyzing the beam parameters. This work is carried out in frame of the Medipix Collaboration and the Munich Centre for Advanced Photonics (MAP).

Speaker: Dr Carlos Granja (Institute of Experimental and Applied Physics, Czech Technical University in Prague, Horska 3a/22, 12800 Prague 2, Czech Republic)

91 Towards ion spectroscopy for hadron beam therapy – finding optimal settings of the Timepix detector

In radiation therapy with ions heavier than protons nuclear fragmentation processes occur. Interactions of the projectile ions with tissue result in a spectrum of lighter ions which have a linear energy transfer and thus a radiobiological effectiveness different from the primary particle type. In order to correctly calculate the biological effect of ion beams it is important to know the complex radiation spectra resulting from the primary beam in different tissue depths and their spatial distribution. Up to now ion spectroscopic measurements have employed large experimental apparatus and could thus obtain data only outside of targets. We however aim for performing spectroscopic measurements directly within phantoms to study fragments evolving from the primary particle beams in therapy-like situations. For this purpose, we use the position-sensitive semiconductor pixel detector TimePix which allows the detection of single particles with per pixel energy-sensitivity. The device can thus directly determine the energy loss along particle trajectories in silicon. Data are collected via an integrated USB-based readout interface and can be visualized online with the Pixelman software. The charge distribution created in the detector by an individual ion extends to several pixel forming a cluster. The spatial distribution of the irradiation pattern can be analyzed. Different cluster parameters like size and energy per pixel do not depend only on the incoming particle type but also on the detector settings, especially the applied bias voltage. To allow for good discrimination between different particle types we looked into optimal detector settings. Measurements were performed at the Heidelberg Ion Beam Therapy Center. The detector was placed perpendicular to the beam without any material in front of it and irradiated with mono-energetic proton and carbon ion beams of energies between 48 and 410 MeV/u. Different detector parameters (bias voltage, ikrum value, acquisition time) were applied. The obtained cluster size, cluster energy and the ratio of both strongly depend on the applied sensor bias voltage. When using optimized detector settings, differences found in the cluster size and the energy per pixel distributions show the possibility to differentiate between carbon ion and proton induced events. This work has been carried out in frame of the Medipix Collaboration.

Speaker: Ms Bernadette Hartmann (German Cancer Research Center (DKFZ))

92 Utilization of a pnCCD detector for Synchrotron radiation experiments: Application study of Interdiffusion in Metallic Thin Films

Developments in synchrotron radiation facilities have provided photon fluxes in the order of 1014 photons/sec and higher. To utilize such high fluxes in particular experiments it is important to provide detectors that handle such fluxes, operate with fast frame rates and resolve at the same time events in the spatial coordinates with reasonable energy resolution. This study characterizes a pn-CCD pixel detector [1] as a function of high photon fluxes and high frame rates. Experimentally, different photon rates, faster charge transfer clocking and different frame rates were probed and the validity of delivered data was studied. For low photon rates the concept the detector is operating in the single photon detection. However, for higher count rates this concept does not work anymore but alternatively the detector can operate in so called integration mode. For this type of applications it is necessary to investigate the full well capacitance of the detector pixels. As instructive example of application of pnCCD we present in-situ studies of thermally induced inter diffusion in thin Fe/Pt multilayer films [2]. Such kind of applications produces distinguished structural peaks (Bragg reflections) with a high local intensity and characteristics that change as a function of time and temperatures. Here the particular advantage of the energy dispersive detector is to perform measurements simultaneous over a wide energy band including characteristic L-absorption edges of Pt. This allows for determination of element specific interdiffusion. The experiments performed were used to build-up a model for the detector response under high fluxes and increasing frame rates. [1] N. Meidinger et al., Nucl. Instr. and Meth. A, 2006, 565, 251-258 [2] N. Zotov, J. Feydt, A. Savan and A. Ludwig, Journal of App. Physics 100, 073517 (2006).

Speaker: Mr Ali Abboud (Student)

Slides Utilization_of_a_pnCCD_detector_for_Synchrotron_radiation.pdf

93 Three-dimensional Dose Verification Using Normoxic Polymer Gel Dosimeters for Tomotherapy

The aim of this study is to evaluate the feasibility of using MAGAT as a near real-time 3-dimensional dose measurement device for tomotherapy. MAGAT is a new type of normoxic polymer gel dosimeter, which responses well to absorbed dose and can be easily made in the presence of normal oxygen surroundings. Its dose response was measured by irradiating MAGAT-gel-filled testing vials with tomotherapy and its linear relationship with dose was present from 0 to 6.5 Gy. One group of gel samples were measured in near real-time, in which the gel phantom was read right after the irradiation. The other group was measured 12 hours after irradiation so the gel phantom can be exposed to oxygen. Several post-imaging processing filters including Nagao, Guess, median, mean, min and max, were applied on megavoltage computed tomography (MVCT) images for better discrimination on dose responses. Our results show that dose responses for MVCT with real-time and 12-hour delayed measurement were 4.76 and 4.69 ΔSI．cGy-1, respectively, and show no significant difference (p-value = 0.72). For study of the filtering effects, Gauss, median and mean filters offer better linear correction coefficients of dose response. In conclusion, the MAGAT polymer gel dosimeter read from MVCT imaging is a promising method for dose verification in clinical tomotherapy.

Speaker: Prof. Tzung-Chi Huang (China Medical University)

Paper Gel_Paper.docx

Poster poster-iWorid2011-gel.ppt

Slides miniTalk.ppt

13:00 Lunch Break

Imaging: 3 contributions

Convener: Mr Seppo Nenonen (Oxford Instrumenst Analytical oy)

94 Femtosecond X-ray Imaging using Free Electron Lasers

The development of free electron lasers in the X-ray regime has opened up new frontiers in X-ray imaging. With X-ray pulses of only a few femtoseconds duration and sufficient peak power to produce high-quality diffraction patterns from a single pulse, recent experiments at the Linac Coherent Light Source (LCLS) have demonstrated structural determination from both isolated viruses and streams of hydrated sub-micron crystals. Samples are continuously fed into the X-ray focal region producing a diffraction pattern each time a sample particle happens to intersect the FEL beam, with these ‘hits’ occurring at a rate dependent on sample concentration. Such experiments push the limits of detector technology: femtosecond diffraction requires integrating detectors with single-photon sensitivity and high dynamic range capable of reading out full frames at the machine repetition rate (120Hz in the case of LCLS). Typical data sets consist of many millions of images. Here, we will discuss our experiences to date using high-frame-rate imaging detectors at LCLS, describe the essential characteristics of the measured X-ray diffraction patterns, and look ahead to detector requirements for future femtosecond diffraction experiments at upcoming free electron laser sources.

Speaker: Dr Anton Barty (Center for Free Electron Laser Science)

95 Equalization of Medipix2 imaging detector energy thresholds using measurement of polychromatic X-ray beam attenuation

The single photon counting pixel detector Medipix2 is a powerful tool for energy resolved X-ray imaging. It allows discriminating energy of incoming X-rays by setting an energy threshold common to all pixels. As parameters of individual pixels vary, each pixel further contains a 3-bit digital-to-analogue converter (DAC) adjustment. Values of these DACs are traditionally determined by finding the noise floor in each pixel. Our approach is based on a polychromatic X-ray beam attenuation measurement. An attenuation curve is measured using varying thickness of aluminium foil. The attenuation curve is fitted in each pixel with a function calculating the detected signal. Free parameters of the fit are the beam intensity and the energy threshold. The measurement is done twice, with the threshold adjustment set to minimum resp. maximum value in all pixels. The result is a calibration of the adjustment DACs, allowing finding the value of the adjustment DAC in each pixel such that the dispersion of energy thresholds between pixels is minimized. It is a fast and simple to use method that does not require modification of the imaging setup. It will be shown that it reduces the dispersion of threshold values by up to 40% compared to the noise-floor based technique of equalization.

Speaker: Dr Josef Uher (CSIRO PSE)

Slides 2011-06-10_MPX_BH_equalisation.pptx

96 Phase contrast imaging of lightweight objects using microfocus X-ray source and high resolution CCD camera

Modern laboratory X-ray imaging systems with microfocus source and CCD camera give us the possibility to move some of modern imaging techniques from synchrotrons to laboratories. Spatially coherent X-rays emited from microfocus source traverse a sample with phase shift. Beam deflection induced by the local change of refractive index may be expressed as dark-bright contrast on the edges in final projection. These phenomena lead to increase of spatial resolution of X-ray projections but may also lead to unpleasant artifacts in computerized tomography (CT) unless reconstruction program can separate phase and absorption contributions. In this contribution several results of phase constrast imaging are presented.

Speaker: Mr Zaprazny Zdenko (Slovak Academy of Sciences)

Slides

• 3p21Voltex.mpg
• hlava_muchy4.mpg
• polystyren.wmv
• Zaprazny_IWORID_2011.ppt

Poster Mini Talks VI

Convener: Mr Seppo Nenonen (Oxford Instrumenst Analytical oy)

97 Laboratory X-ray microscopy with a nano-focus X-ray source

X-ray microscopy setups based on the principle of geometric magnifcation are attractive for laboratory setups because of the simplicity of the concept as well as the possibility to use a wide range of photon spectra. However, in such setups the focal spot size of the source limits the spatial resolution that is achievable. Therefore an X-ray source providing a nanometer sized focal spot is needed to achieve resolution in the nanometer range. Conventional state-of-the-art micro- and nanofocus X-ray tubes provide focal spot sizes in the range of 700 nm to 900 nm, some manufacturers claim sizes down to 250 nm in their product flyers. We are using the electron gun and optics of an electron probe micro analyzer as the basis for our nanofocus X-ray source. To minimize the X-ray focal spot not only the focussing of the electron beam is important but also the interaction of the electron beam and the target material. Using the Monte-Carlo X-ray simulation ROSI [1] we calculated the optimal tungsten layer thickness for different types of targets, providing either high resolution or high X-ray flux. Compared to a standard target we could achieve a substantial reduction in focal spot size (up to 1/3) with the high resolution target or a significant gain in X-ray flux (more than a factor of 3) with the high flux target. The photon flux, however optimized, is still low compared to conventional X-ray sources. Thus a photon counting detector is required to allow imaging free of electronic noise. We use the Quad version of the Medipix2 MXR detector [2]. It consists of 512 x 512 pixels with a pixel size of 55 µm x 55 µm and has a 300 µm silicon sensor layer. In this paper we present the process of target optimization and will compare simulated results with measurements of focal spot size and X-ray flux. Also, resolution tests and imaging examples from applications will be shown. References: [1] J. Giersch, A. Weidemann, G. Anton, Nuclear Inst. and Methods in Physics Research A, 509:151–156, 2003. [2] X. Llopart, M. Campbell, R. Dinapoli, D. San Segundo and E. Pernigotti; IEEE Trans. Nucl. Sci. NS49 (2001), p. 2279.

Speaker: Mr Frank Nachtrab (Cluster of Excellence "Engineering of advanced materials" EAM, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany)

Slides minitalk_nachtrab.ppt

98 3D particle distribution in Water Phantom in Therapy Beam

Hadron therapy uses ion beams for irradiation of tumorous tissue. Ions have highly localized dose deposition in contrast to photon radiation. A main advantage of ions is that they deposit the most of energy at the end of their range according to the Bragg curve. Unfortunately the ion beams often generate a substantial amount of secondary particles with longer range. Thus certain fraction of dose is deposited by other than primary ions outside of the planned volume. The observation of all ionizing particles accompanying the ion beam as well as the direct measurement of particle energy loss, trajectory, local energy deposition and lateral straggling can be directly provided by the semiconductor detector Timepix (256 × 256 pixels with 55 µm pitch). This device operates as an active nuclear emulsion providing visualization of particle traces. Analysing shapes of the characteristic particle traces we can distinguish primary ions from secondary particles. Measurements were performed at the Heidelberg Ion Beam Therapy Center (HIT) with using medical carbon ion and proton beams. Narrow beams to size 3mm were directed onto a water tank phantom of size 355 x 355 x 420 mm3. The pixel detector was immersed in water inside the phantom and its location was controlled by a remote positioning system allowing 3D scanning of radiation field. Full scans were performed with two different beams: carbon 270 MeV/u and protons 143 MeV. The radiation field was evaluated in 24 detector positions.We tested both detector plane orientations: parallel and perpendicular with respect to the beam axis. In each point the shapes of recorded tracks were evaluated and distributions of appropriate particles were created. The results show the different ranges of different types of secondary radiation. This work is carried out in frame of me the Medipix collaboration.

Speaker: Lukas Opalka (FBME, Czech Technical University in Prague, Kladno, Czech Republic)

Slides opalka_iworid2011.ppt

99 Application of a pnCCD in protein crystallography

The fast and precise determination of crystal structures using the Laue diffraction method requires a simultaneously position- and energy-resolved detection of photons. By means of a back side illuminated pnCCD with frame-store operation [1] the spatial distribution of Laue spots as well as their energies can be measured at the same time. The sensitive volume consists of a fully sideward depleted n-Si layer of 450µm thickness subdivided into 256x256 pixels of 75µmx75µm size with a typical readout frequency of about 120Hz. The system has found applications for soft and hard X-rays [2,3]. Using white synchrotron radiation the pnCCD delivers a three-dimensional intensity distribution spanned by two pixel directions and an energy direction covering a 3D data volume in reciprocal space which is expanded to 4D in case of dynamic measurements. In this sense the system provides a good possibility to investigate unknown crystal structures in arbitrary orientations in space as well as structural phase transitions at fixed scattering geometry. Previously it was shown that the crystallographic unit cell of a tetragonal LiAlO2 crystal can be determined from the three-dimensional pnCCD data sets without any a priori information about the sample [4]. Consequently the energy-dispersive Laue diffraction is a powerful technique for single shot structure analyses in protein crystallography. In the subsequent application the potential of the pnCCD is exploited to investigate small organic crystals exhibiting complex structures and weak scattering signals. As a test example the energy-resolved Laue pattern of a hen egg white lysozyme single crystal is considered in transmission geometry and used for structure determination. In such kind of experiments the detector system is operated in a combined energy-dispersive single photon counting and integration mode. [1] N. Meidinger et al., Nucl. Instr. and Meth. A 565, 251-258, (2006) [2] L. Strüder et al., Nucl. Instr. and Meth. A 614, 483-496, (2010) [3] W. Leitenberger et al., J. Synchr. Rad. 15, 449-457, (2008) [4] S. Send et al., J. Appl. Cryst. 42, 1139-1146, (2009)

Speaker: Sebastian Send (University of Siegen, Germany)

100 Improving the spatial resolution of a soft X-ray Charge Coupled Device (CCD) used for Resonant Inelastic X-ray Scattering

The Super Advanced X-ray Emission Spectrometer (SAXES) [1] at the ADRESS beamline [2] of the Swiss Light Source (SLS) is a high-resolution X-ray spectrometer used as an end station for Resonant Inelastic X-ray Scattering at 400 to 1600 eV [1]. It disperses photons across a CCD, allowing the energy of scattered photons to be determined by the spatial position. The limiting factor of the energy resolution is currently the spatial resolution achieved with the CCD, reported at 24 μm FWHM [1]. Electron clouds are formed by interactions in the ‘field free’ region of the back-illuminated CCD. These clouds diffuse in all directions whilst being attracted to the electrodes, leading to events that are made up of signals in multiple pixels. This allows centroiding techniques to be used to improve the CCD spatial resolution and the energy resolution of SAXES. The PolLux microscopy beamline at the SLS [3] produces an X-ray beam with a width of down to 20 nm. The images produced from scanning this beam across CCD pixels (~15 μm^2) can be applied to produce event recognition algorithms to match event profiles to photon interactions in a particular region of a pixel. This information can help improve the software analysis currently used at SAXES, improving the energy resolution. [1] G. Ghiringhelli, et al., Rev. Sci. Instrum., vol. 77, 113108, 2006. [2] V. N. Strocov, et al., J. Synchrotron Radiat., vol. 17, 631-643, 2010. [3] J. Raabe, et al., Rev. Sci. Instrum., vol. 79, 113704, 2008.

Speaker: Mr Soman Matthew (Open University)

Poster Matthew_Soman_ID216_Poster.pdf

Slides Matthew_Soman_ID216.pdf

101 Detective quantum efficiency of photon-counting detectors having edge-on geometry under mammography imaging condition

We analyze the imaging performances of the microstrip silicon detector operated in counting mode under mammography imaging condition. Although the detector has an asymmetric pixel size of about 100 (width) by 500 (height) microns, the 100-micron slit aperture of the beam collimator shapes a practical symmetric pixel pitch of 100 microns. Since the detector is composed of four separate linear array modules and each module has 256 microstrip designs, the whole image size can be covered over 10 cm times the scan length. The detector has edge-on geometry with an angle of 5 degrees to the normal direction of x-ray incidence. Using a slanted-edge knife technique, the modulation-transfer function (MTF) without aliasing is determined. Noise-power spectrum (NPS) is determined using two-dimensional Fourier analysis on the scanned images. Based on the measured MTF and NPS results, detective quantum efficiency (DQE) is calculated. This systematic procedure is applied to the various thresholding operations in the detector. Asymmetric MTF properties between two perpendicular directions are observed and the noise-power spectral densities are white for spatial frequencies. The best DQE around zero-spatial frequency is greater than 0.8, which is still less than the theoretical limit, is achieved. The measured imaging performances are analyzed by a combination of cascaded linear-systems theory and Monte Carlo simulation in detail and compared with those of conventional charge-integrating detectors.

Speaker: Mr Seungman Yun (Pusan National University)

Poster 11iWoRID_DxRay_upload.pdf

102 Integrated USB based readout interface for silicon strip detectors of the ATLAS SCT module

An integrated portable USB based readout interface for the ATLAS semiconductor trackers (SCT) has been built. The ATLAS SCT modules are large area silicon strip detectors designed for tracking of high-energy charged particles resulting in collisions on Large Hadron Collider (LHC) in CERN. These modules can be also used on small accelerators for medical or industry applications where a compact readout interface would be very useful. The new interface which has been constructed provides integrated power, control and DAQ with online easy configurable communication between the detector module and the controlling PC. The interface is based on the Field Programmable Gate Array (FPGA) and the high speed USB 2.0 standard. This design permits to operate the modules under high particle fluency while minimizing the dead time of whole detection system. Utilization of programmable device simplifies the maintenance and permits future expansion of the functionality without any hardware changes. The device includes the high voltage source for detector bias up to 500 V and it is equipped with number of devices for monitoring the conditions of measurment (temperature, humidity, voltage). These features are particularly useful as the strip detector must be operated in well controlled environment. The operation of the interface will be demonstrated on data measured with different particles from radiation sources.

Speaker: Mr Petr Masek (IEAP CTU in Prague)

Poster iworid_poster_v3.pdf

Slides iworid_minitalk_v1.pdf

103 Measurement of secondary radiation with the pixel detector Timepix during ion beam therapy

In ion beam therapy the finite range of the ion beams in tissue and the presence of the Bragg-peak are exploited. Unpredictable changes in the patients condition can alter the range of the ion beam in the body. Therefore it is desired to verify the actual ion range during the treatment, preferably in a non-invasive way. Positron emission tomography has been used successfully to monitor the precision of the applied dose distributions. This method however suffers from limited applicability and low detection efficiency. As an alternative to photons, in this study we investigate the possibility to measure secondary charged particles and to increase the detection efficiency. An initial experimental study to register the outcoming radiation was performed at the Heidelberg Ion Beam Therapy Center (HIT) in Germany using medical carbon ion beams. A static pencil beam was dumped in a PMMA block and the emerging secondary radiation was measured with the position-sensitive Timepix detector outside of the phantom. The detector, developed by the Medipix Collaboration, consists of a silicon sensor connected to a pixelated readout chip (256 × 256 pixels with 55 um pitch). Timepix can operate as an active nuclear emulsion registering single particles online with 2D-track visualization. The shape of the tracks together with the measurement of the deposited energy in each pixel allows drawing conclusions on the radiation type, energy and position. The direction of the particles are readily determined by using more-layered detectors. Measurements were performed at different distances from the beam impact point on the block, corresponding to the plateau, Bragg-peak, tail and behind. Distributions of the registered tracks were analyzed as a function of quantities like the track shape and deposited energy. Due to the observed clear correlation with the depth, the Bragg peak position can be possibly determined from the measured data. This work is carried out in frame of the Medipix Collaboration.

Speaker: Dr Maria Martisikova (German Cancer Research Center)

104 Micro-tomographic study of metal grainy structure

X-ray transmission radiograms of Aluminum alloy contain features induced by variations of the material chemical composition. Generally, material variations are strongly connected with grains of the metal, where the material composition of one individual grain is more or less homogenous. However, material composition varies from one grain to other. Grains of the studied material have typically dimensions 10 micrometers in diameter and 100 micrometers in the length. The material variations can enable the observation of geometry and orientations of individual grains in the specimen volume using a highly sensitive and high resolution detector together with advanced X-ray micro tomographic method. Observation of such tiny structures requires high dynamic range of acquired radiograms with high signal to noise ratio and appropriate geometrical magnification. These requirements can be fully satisfied using single photon counting device Medipix, a precise micro-tomographic setup and appropriate data processing. Results will be demonstrated with Aluminum alloy bar specimen.

Speaker: Daniel Vavrik

Slides ID_232_shortTalk_Vavrik.pptx

105 Mobile system for in-situ imaging of cultural objects

Non-invasive analysis techniques we have recently developed with the pixel detector Timepix have shown great potential for the inspection of the objects of cultural heritage. We have newly developed the instrumentation and methodology for in-situ X-ray transmission radiography and X-ray fluorescence imaging. With the methods successfully tested we are evaluating the mobile system for remote terrain tasks. The prototype of a portable imaging device has been designed. It comprises the radiation source tube and the spectral sensitive X-ray camera. Both components are mounted on independent motorized positioning systems allowing adaptation of irradiation geometry to the object shape. Both parts are placed onto a pair of universal portable holders (tripods). The detector is placed in a shielded box with replaceable entrance window (beam filters and pinhole collimator). This flexible setup allows performing in-situ measurements for both transmission and emission (XRF) radiography. The assembled system has been successfully tested in our laboratory with phantoms and real samples. The obtained and evaluated results are presented in this paper. Future work includes an adaptation of the current system for real in-situ utilization and preparation of software allowing semi-automatic remote control of measurement.

Speaker: Mr Jan Zemlicka (IEAP CTU in Prague)

Slides minipresentation_Zemlicka_(Iworid_2011).pptx

106 Performance evaluation of a PET demonstrator for PET-MR imaging based on monolithic LYSO:Ce scintillators

We are developing a positron emission tomography (PET) insert based on avalanche photodiodes (APDs) arrays and monolithic LYSO:Ce scintillators with the aim of being used for human brain studies inside a clinical 3T MRI equipment. In a previous work [1], we demonstrated the performance of our detectors by implementing an experimental setup consisting of two monolithic blocks working in coincidence, which were read out by the first version of an application specific integrated circuit (ASIC), followed by both external coincidence and digitalization modules. This preliminary demonstrator showed good spatial resolutions at detector level and good imaging qualities, which achieved reconstructed images of Na-22 point sources with spatial resolutions of 2.1 mm FWHM. Nevertheless, we detected image distortions and compressions due to the non-linearities close to the edge of the crystals and the absence of neighbor blocks. In this work we report on the performance evaluation of a larger scale PET demonstrator with higher field of view (FoV), which is based on the new updated ASIC (VATA241) [2] and is formed by two sectors of monolithic detector blocks placed face-to-face. Doing so, we obtain a better evaluation of the imaging capabilities of our BrainPET scanner. Moreover, the new prototype demonstrator has been built for validating the data readout architecture, the coincidence processing implemented in a Virtex 5 field programmable gate array (FPGA), as well as the continuous training method required to determine the points of entrance over the surface of our monolithic detector blocks. References [1] I. Sarasola, et al., "PET Demonstrator for a Human Brain Scanner Based on Monolithic Detector Blocks," IEEE Trans. Nucl. Sci., [accepted, under minor revisions] [2] I. Sarasola, et al., "A novel front-end chip for a human PET scanner based on monolithic detector blocks," 12th International Workshop on Radiation Imaging Detectors IWORID2010, Jan. 2011, JINST 6 C01034 2011.

Speaker: Icíar Sarasola (CIEMAT)

Poster Poster_BrainPET_Zurich_2011.pdf

Slides iWoRID_BrainPET_Sarasola.pdf

107 A Range Verification Method for Proton Therapy using a Photon Counting Detector

A range verification method plays an important role in the quality assurance of the proton therapy offering the high conformity and reduction in radiation dose. To localize the distal falloff of the dose distribution, secondary particles (C-11, O-15, N-13) produced by the proton interaction within the patient body can be used as a measure of the beam range. We proposed a multi-modality imaging system for X-ray and gamma-ray coincidence imaging using a single CdZnTe detector to measure proton range verification. The detector system consists of two parallel planes of detectors and an X-ray generator. An X-ray image is acquired using one detector for the verification of 2-dimensional anatomical structure of the patient, and the paired gamma rays from the annihilation are imaged with two modules to determine the maximum range of proton penetration. Image registration is intrinsic because the X-ray and gamma ray images are acquired in the same geometry. 110 MeV proton beam, a cylindrical tissue phantom, and two rectangular CdZnTe detectors were modeled, and the imaging performance of this system was evaluated using GATE simulation. The results showed the potential benefits of a X-ray/gamma-ray imaging with a single detector for range verification in proton therapy.

Speaker: Prof. Jin Sung Kim (Samsung Medical Center)

Poster 2011_iworid_포스터_최종본_real.ppt

108 Monte Carlo simulations on performance of double-scattering Compton camera

Compared with conventional gamma-ray emission imaging device based on mechanical collimation, the Compton imaging technique based on so-called ‘electronic collimation’ could provide better performance in terms of imaging resolution and sensitivity when the gamma-ray source to be imaged has relatively high energy, i.e., more than a few hundreds keV. We have developed a prototype double-scattering Compton camera which consists of two double-sided silicon strip detectors (DSSDs) for scatter detectors and a cylindrical NaI(Tl) scintillation detector for absorber detector for nuclear decommissioning applications and particle therapy applications both of which involve imaging high energy gamma-ray sources. The basic idea of the double-scattering Compton camera is to maximize the imaging resolution by measuring two successive interaction positions of Compton scattering very accurately because the imaging resolution is mostly limited by the spatial resolution of the component detectors which consequently affects the accuracy in determining the axis of the reconstruction cone. In the present study, the performance of the double-scattering Compton camera was compared with that of a single-scattering Compton camera with similar dimensions as a function of the source energy by using Geant4 Monte Carlo simulations. The optimal geometry of the multiple-detector-type double-scattering Compton camera was also studied by comparing the performance of the Compton camera for two extreme cases, that is, when the additional scatter detectors are placed in the planar direction and in the axial direction. In addition, the performance of the double-scattering Compton camera was evaluated when additional side absorber detectors were used to register the double-scattered photon in the backward direction. In this case, we can easily expect that the imaging sensitivity will be enhanced; however, the imaging resolution could be degraded by the increase of the number of events with wrong interaction sequences. We hope that the results of this simulation study will provide a guideline to researchers to find a proper design of Compton camera for a given objective.

Speaker: Mr Jin Hyung Park (Department of Nuclear Engineering, Hanyang University)

Poster 11_iworid_Poster_Park.pptx

109 Preliminary Study on Neutron image using new crystal scintillator

Neutron detection is a very difficult work because it directly does not generate secondary charge particles. So far, (n, n) elastic scattering or (n, x) nuclear reaction leading to emission of charged particle is the most common detection methods. In recent year there is an increasing interest in neutron imaging method. In the low-energy range there are several materials that can be classified as the capability for determining neutron energy spectrum and for discriminate against gamma-ray. Currently, we are interested in the newly grown crystal like these Cs2LiGdCl6(Ce) and Cs2LiCeCl6 crystals. This one’s emission band is from 385 nm to 405 nm, that one’s is in between 360 nm and 460 nm. The decay time of this one’s is about 557 nsec and that one’s is 573 nsec for gamma-ray. These decay times is longer than of the common used neutron scintillator as like BC501A, stilbene crystal. They include the Li component and this nuclide can reacts with neutrons according to 1n + 6Li → 3H + 4He, and Ge nuclide is also candidate for neutron detection material. In this study, we measured the optical characteristic of these materials in order to study the capability of the pulse shape discrimination for detecting neutron against gamma-ray. The absorption band of the silicon based photo-detectors are usually is from 350 nsec wavelength and has the peak at about 450 nsec. This wavelength is proper condition to couple with the new neutron detection material. We test the capability of the new neutron image system that was consists of the new crystal and silicon based photo-diode. This study is supported by Ministry of Knowledge Economy through KEIT(10030104).

Speaker: Dr Hyunduk Kim (Department of Nuclear and Quantum Engineering, Korea Advanced Istitute of Science and Technology)

110 Semiconductor pixel detector with absorption grid as a tool for charge sharing studies and energy resolution improvement

The state-of-the-art hybrid semiconductor pixel detector Timepix allows direct measurement of energy of each detected particle. Based on this detection principle, completely new applications like energy sensitive (color) X-ray radiography or fluorescent X-ray imaging have been introduced. The performance of these methods (for example the feasibility to separate two different materials in the radiogram) is given by the spectral resolution of the detector. The energy resolution of the pixelated detector is, however, influenced by the charge sharing effect. This effect originates from the fact that the charge created by the incoming particle spreads out between several adjacent pixels (depending on the place of interaction and detector parameters). In the single particle counting detectors, the charge collected in each pixel is compared with a certain threshold level and, if it is lower, the event is not registered and the charge is lost. As a consequence, the energy resolution of these detectors is deteriorated. In this contribution we present a novel approach for characterization of semiconductor pixel detectors using X-rays. We use a precise gold grid placed in front of the sensor chip, segmenting the incoming X-ray beam into a matrix of precisely defined micro-beams irradiating all the detector pixels in known positions. The proper analysis of obtained moiré pattern allows evaluation the charge sharing effect and determination of its influence to spectrometric properties of the detector. Instead of a synchrotron source, simply the fluorescent radiation generated by a standard X-ray tube can be used as a source of monochromatic X-rays. The size of all micro-beams is limited just by the production technology of the aperture. As opposed to currently used micro-beam studies realized at synchrotron sources, the whole pixel matrix is investigated at once. This offers a great tool for the investigation of charge sharing phenomena and verification of theoretical works dedicated to these detectors. The similar absorption grid can be used for masking of pixel borders suppressing the charge sharing effect. This approach significantly improves the spectrometric properties of pixelated detector at the cost of lower detection efficiency. This technique can be used for energy sensitive X-ray imaging of inanimate objects where the radiation dose does not present an issue.

Speaker: Mr Frantisek Krejci (IEAP CTU in Prague)

Slides Krejci,_Iworid_2011,_mini-talk_3.ppt

111 Smart dosimetry by pattern recognition using a single photon counting detector system in time over threshold mode

The function of a dosimeter is to display the absorbed dose of radiation, where a particular type of radiation is usually targeted. Recently, there have also emerged applications where all kinds of radiation are absorbed and sorted by pattern recognition, such as the Medipix2 application in [1]. This form of smart dosimetry enables measurements where not only the total dosage is displayed, but also the distribution of different types of radiation impinging on the detector surface. Furthermore, the use of a photon counting system in “time-over-threshold” mode, where the energy deposition can be measured in each individual pixel, ensures measurements with high accuracy of the pattern recognition. In this article a Timepix [2] detector system working in “time-over-threshold” mode has been used for a smart dosimeter for alpha, beta and gamma radiation. The particle tracks impinging on the detector surface are read out and image processing algorithms are used to classify each particle hit. The individual hits are calculated and the dosage for each type of radiation is given as a result. In some cases, several hits can impact in roughly the same place, forming connected hits. In order to handle this problem, a hit separation method has been added to the pattern recognition algorithm. When the hits have been separated, they are classified by shape and sorted into the correct type of radiation. The algorithms and methods used in this dosimeter have been developed to be simple and computationally effective, in order to enable implementation on a portable device. [1] Holy T., Heijne E. H. M., Jakubek J. Pospisil S., Uher J., Vykydal Z., “Pattern Recognition of Tracks Induced by Individual Quanta of Ionizing radiation in Medipix2 Silicon Detector”, Nuclear Instruments and Methods, sect. A, 2008. [2] Llopart X., Ballabriga R., Campbell M., Tlustos L, Wong W., Nuclear Instruments and Methods, section A, 581 (2007) 485.

Speaker: Mr Salim Reza (Mid Sweden University)

Slides Presentation_SalimReza.pptx

112 Use of the Medipix2 Based CdTe Microprobe in Dental Imaging

For medical imaging devices and techniques the emphasis is generally put on obtaining high resolution and low dose images of samples or patients. Hybrid single photon counting devices together with new sensor materials and advanced techniques of image reconstruction makes this requirement more feasible. In particular cases like direct observation of dental implants also the size of the imaging device itself plays critical role. This work presents the comparison of the images from the commercial dental imaging system with the images from Medipix2 USB Lite devices equipped by Si and CdTe sensor. The single photon counting nature of the Medipix2 chip allows virtually unlimited dynamic range of the images and thus increases the contrast significantly. The dimensions of the USB Lite device are reduced to 15 mm x 60 mm (which means that 25 % out of the total device size is actually sensitive area). Detector of this size can be used directly inside the patients’ mouth.

Speaker: Mr Zdenek Vykydal (IEAP CTU in Prague)

Slides Vykydal_IWORID2011_noanim.pdf Vykydal_IWORID2011.ppt

113 “Double-layer” Method to Improve Image Quality of Industrial SPECT

In industrial processes, multiphase flow is frequently encountered and it is important to examine the phase distribution and flow pattern for the optimization and maximization of the process efficiency, the safe operation and considerable cost savings. In the respect, the industrial process tomography (IPT) technique, the Single Photon Emission Computed Tomography (SPECT) which can provide cross-sectional images by using a injecting radioisotope tracer in a flow system, is considered as one of the most suitable techniques. Currently the Korea Atomic Energy Research Institute (KAERI) and Hanyang University are collaborating to develop an industrial SPECT that is composed of 24 NaI(Tl) scintillation detectors installed in lead collimators in a hexagonal configuration. In this study, a very simple method called “double-layer” method is proposed to improve the image quality of the industrial SPECT. The rationale of the method is using two layers of the identical SPECTs to increase the number of data acquisition views, i.e., from 6 to 12 angles in the present case. For this purpose, one industrial SPECT is rotated by 30 degrees with respect to another SPECT. The performance of the double-layer method was predicted by Monte Carlo simulations using MCNPX and Geant4 for different gamma sources, Tc-99m (Eγ = 140 keV) and Ga-68 (Eγ = 1,077 keV), and then the reconstruction images with 2 cm of spatial resolution were obtained by the maximum likelihood-expectation maximization (ML-EM) algorithms with 50 iterations. To quantitatively evaluate the performance of the double-layer method, the normalized root mean square error (NRMSE) was calculated. The simulation results were very prominent; that is, the double-layer method significantly improves the image quality of the industrial SPECT, especially when the distribution of radioactive tracer is not simple in the flow system.

Speaker: Prof. Chan Hyoeng Kim (Hanyang University)

15:40 Coffee Break

Poster Exibition

18:00 Guided tours Zurich historic center

Wednesday, 6 July

08:00 Bus Transfer to PSI

This day is scheduled to take place at the Paul Scherrer Institute.

114 Welcome at PSI

Speaker: Dr Kurt Clausen (Paul Scherrer Institut)

Applications II: 2 contributions

Convener: Dr Thilo Michel Michel (Erlangen Centre for Astroparticle Physics)

115 From proof-of-principle to daily operation: Pixel detector technology opens up new avenues in scanning imaging

PILATUS technology has been developed over several years from a first proof-of principle to a commercial detector in daily operation in many laboratories around the world. Alongside with this development, scanning imaging with 2D detectors has seen a rapid development and is meanwhile applied in many biomedical and materials science applications. The methodological developments enabled by state of the art pixel detector technology gained so much momentum, that current detection systems are not just fully utilized but actually already limiting further advances: Science cases for the next generation single photon counting and charge integration detectors are readily available. Examples from the fields of scanning small-angle X-ray scattering (SAXS) and ptychographic coherent diffractive imaging will be shown. Utilization of current detector technology as well as limitations and how they may be overcome by ongoing developments in the detector community will be sketched.

Speaker: Dr Oliver Bunk (Group leader Coherent X-ray Scattering, SLS, PSI)

116 Small Dosimeter based on Timepix device for Internation Space Station

The radiation environment in space is different than on Earth. The standard detection methods that are used nowadays fails. The reason is that most of the dose comes from interactions of heavy ions, mainly protons, that are not present on Earth. Measuring a track of particles and their deposited energy allows us to distinguish different particles. This information can be used for sorting of particles into different categories. It is possible to distinguish light particles and ions. Moreover Linear Energy Transfer (LET) for ions can be determined. Each category is assigned a quality factor corresponding to the energy a particle would deposit in human tissue. By summing the dose of all particles an estimate of total dose rate can be calculated. Timepix detector possesses suitable properties for measurements of this type. It is a position sensitive pixelated detector (300 µm thick silicon sensor, 256x256 square pixels with 55 µm pitch) developed at CERN in a frame of Medipix collaboration. This ability to visualize tracks of ionizing particlees was already demostrated. For the dosimetry purposes a miniature device with Timepix detector and integrated USB interface has been designed. The entire device has dimensions of USB flash drive. The device is connected the whole measurement time to a control PC. The PC runs a software that controls data acquisition, adjust acquisition time adaptively according to particle rate, analyzes particle tracks, evaluates energy and LET and visualizes in a simple display an estimated dose rate. The properties of the device will be tested during a mission on International Space Station planned towards the end of year 2011.

Speaker: Daniel Turecek (IEAP CTU in Prague)

Slides 02-talk_turecek_final.pdf

117 Use of Timepix chip for streak imaging in Transmission Electron Microscopy

Lorentz microscopy is a specialised branch of TEM that enables observation of domains and domain wall structure for ferromagnetic samples and is used extensively at the University of Glasgow. Lorentz mode and TEM in general are imaging techniques with very good spatial resolution; however they are limited in temporal resolution for imaging dynamic processes. We have devised a technique for gaining temporal resolution based on streak imaging. Specifically we are studying the injection of domain walls into nanowires by pulsed magnetic fields. This field serves a secondary purpose as it also deflects the electron beam producing a streak. This linear temporal modulation of the image allows us to gather information about the dynamic process. Current TEM CCD cameras are typically limited to millisecond exposure times and add noise with every read; this makes them unsuitable for our use. The Timepix chip however can acquire images on microsecond time scales; this combined with its high detective quantum efficiency make it ideal for our purposes. In collaboration with the particle physics group at the University of Glasgow we have already demonstrated the use of this chip for static imaging at microsecond time scales and shown significant advantages over CCD type detectors. By using the Timepix chip we will present resultant streak images of the dynamic domain wall injection process. These should achieve sub microsecond temporal resolution. Going beyond this, we aim to exploit the unique time-of-arrival mode of the Timepix chip with the aim of reaching temporal resolutions of below 100ns.

Speaker: Dr Damien McGrouther (University of Glasgow)

Slides pres.ppt

10:30 Coffee Break

Free Electron Lasers: 4 contributions

Convener: Dr Heinz Graafsma (DESY)

118 The SwissFEL X-Ray Laser Project

The Paul Scherrer Institute is planning the construction of a X-ray free electron laser (SwissFEL), which will produce 20 fsec pulses of coherent x-rays in the wavelength range 0.1 to 7 nm, with extremely high peak brightness. These characteristics will provide opportunities for new experiments in chemistry, solid state physics, biochemistry and materials science. The presentation will focus on novel applications with the weight on gaining structural information, the description of the fundamental aspects of the planned facility, and last but not least the milestones towards the planned operation.

Speaker: Dr Rafael Abela (Project Leader Photonics, swiss FEL, PSI)

Slides Iworid_14_Abela.ppt

119 Single-Photon Thresholding for Low-flux Measurements in Charge-Integrating Pixel Array Detectors

Many important experiments using next generation light sources produce extremely high instantaneous count rates that preclude the use of detectors that count individual photon pulses. Detectors that integrate and measure the total charge produced by x-ray conversion do not have the same limitation and are better suited to many of the demands of experiments at new sources. Instruments based on a charge integrating pixel array detector (PAD) designed and developed at Cornell University have been installed at the Linac Coherent Light Source (LCLS) for coherent x-ray diffraction imaging (CXI) and x-ray pump probe (XPP) experiments. Even though the ability to measure signal from extremely high count rates is necessary, reaping the full benefit of new sources also requires accurate measurement of extremely low x-ray fluxes incident on the detector. We present data on extremely low-flux diffraction measurements collected with a single module (small-scale) detector in our lab using the same ASIC design used in the LCLS instruments. Mean fluxes of less than 1/10000 x-ray per pixel per frame are used to recover diffraction patterns from large data sets. Thresholding using the high signal-to-noise ratio for single photon measurements and other aspects of data analysis are discussed. This type of data analysis is of particular importance to the CXI experiment because high-q features of diffuse, single-particle diffraction patterns are expected to have extremely low fluxes and many frames of data will be needed to extract meaningful information. At the same time, the detector has to be able to handle the arrival in femtoseconds of hundreds of x-rays per pixel in the low-q region.

Speaker: Dr Hugh Philipp (Cornell University)

Slides iWoRID13Philipp.pdf

Video CNT-Growth1-diffencode.avi.mpg test4-1.m4v

120 The DEPFET Sensor with Signal Compression: a High-Speed Large Format X-ray Imaging Detector for the European XFEL

The DSSC detector system, which is currently under development for the European XFEL, will be able to record X-ray frames with 1 Megapixel at a rate of 4.5MHz. The system is based on a silicon pixel sensor with a newly developed DEPFET as the central amplifier structure. The sensor will have a size of 200x200 mm2 and will be read out by 256 ASICs which are bump-bonded to the detector in order to provide full parallel readout. The signals from the sensor, after being processed by an analog filter, are digitized by 8-bit ADCs and locally stored in an SRAM. In order to fit the dynamic range of 104 photons of 1 keV per pixel into the input range of the ASIC while simultaneously achieving single photon resolution at 1keV, a strong signal compression is required. This compression is achieved by a non-linear characteristic which is inherent to a new DEPFET structure that combines an enhanced charge handling capacity with the excellent noise performance of the DEPFET. The main building blocks of the system will be discussed with a special emphasis on sensor development and simulations. Moreover, we will present measurements with prototype readout ASICs and standard DEPFETs that have shown a very low noise which makes it is possible to achieve the targeted single photon resolution for 1keV photons at a frame rate of 4.5MHz.

Speaker: Dr Christian Sandow (PNSensor GmbH, Munich, Germany)

121 The AGIPD Detector for the European XFEL

The AGIPD consortium consisting of Deutsches Elektronensynchrotron (DESY), Paul-Scherrer-Institut (PSI), University of Hamburg and University of Bonn is developing a pixel detector for the European Free Electron Laser (XFEL) [1]. The challenge is the temporal structure of the radiation pattern emitted by the European XFEL, which will provide fully coherent X-ray pulses with a length of less than 100 fs and an intensity of up to 1012 photons at a photon energy of 12 keV. The pulses will be delivered in bunch trains with a repetition rate of 10 Hz, where each train consists of 2700 bunches with a spacing of 220 ns. The task of creating a detector suitable for the beam characteristics is difficult, as there will be a high number of photons simultaneously impinging the pixels. Thus, as it is not possible to use the photon counting technique, an integration system has been developed. Due to the required high dynamic range of >104 photons, multiple gain stages with an automatic internal switching will be used. Therefore, the AGIPD collaboration developed such a charge integrating hybrid pixel detector with dynamic gain switching and an analogue on-pixel storage chain, which will allow temporal storage of images (~200) during the train, which will be read out in the gap between the trains. The readout chip will consist of 64 x 64 pixels, each pixel having a pixel size of 200 x 200 μm2. The detector will be built out of 8 x 2 modules each containing a silicon sensor bump bonded to an array of 8 x 2 CMOS readout chips. Up to now, several prototype chips have been produced. The AGIPD01 prototype is not pixelated and was used to investigate the different parameters of the electronics like the linearity of the readout chain consisting of a Preamp and a Correlated Double Sampling Stage (CDS) or the gain switching. AGIPD02 includes 16 x 16 pixels with 100 storage cells and bump bonded silicon sensor. Different combination of Preamp and storage cell architecture were employed. AGIPD03 is the latest prototype with a high speed serial control logic and a radiation hard storage cell design. This talk will give an overview of the AGIPD project, focusing on the results of the characterization of the AGIPD01 and AGIPD02 prototypes. [1] European XFEL: http://www.xfel.eu/en/index.php

Speaker: Dr Dominic Greiffenberg (Paul Scherrer Institute (PSI))

Slides Greiffenberg_iWoRiD2011.ppt

122 Study of X-ray Radiation Damage in Silicon Sensors

The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully coherent, high brilliance X-ray pulses per second with duration below 100 fs. This will allow to record diffraction patterns of single molecules and study ultra-fast processes. Silicon pixel sensors will be used to detect the diffraction images. In 3 years of operation the sensors will be exposed to doses of up to 1 GGy of 12 keV X-rays. At these X-ray energies no bulk damage in silicon is expected. However fixed oxide charges in the SiO2/Si3N4 layer and interface traps at the Si-SiO2 interface will build-up. We have investigated as function of the 12 keV X-ray dose the microscopic defects in test structures and the macroscopic electric properties of segmented sensors. From the test structures we determine the oxide charge density and the density of interface traps as function of dose. We find that both saturate (and even decrease) for doses above a few MGy. For segmented sensors the defects introduced by the X-rays increase the full depletion voltage, the surface leakage current and the inter-pixel capacitance. In addition an electron accumulation layer forms at the Si-SiO2 interface which increases with dose and decreases with applied voltage. Using TCAD simulations with dose dependent parameters obtained from the test structures, we are able to reproduce the observed results. This allows us to optimize the sensor design for the XFEL requirements. In addition the Si-SiO2 interface has been studied by time resolved signals induced by 660 nm laser light, which has a penetration of about 3 micrometer in silicon. Depending on the biasing history, humidity and irradiation dose, losses of either electrons or holes or no charges losses are observed. The relevance of these results for sensor stability and performance is under investigation. Keywords: XFEL, silicon pixel sensor, radiation damage, TCAD simulation and charge losses.

Speaker: Mr Jiaguo Zhang (Institute for Experimental Physics, Hamburg University)

12:55 Lunch Break

Front-end Electronics and Readout II: 2 contributions

Convener: Dr Bernd Schmitt (PSI)

123 Pixel detectors in LHC experiments

During the past 20 years pixel detectors have advanced into precise tracking devices used in particle physics experiments. Since 2008 they have been successfully used in three LHC experiments: Alice, Atlas and CMS. What made these detectors difficult to build were the strict requirements for high readout speed, resistance to very high level of radiation and low mass. All three LHC pixel detectors have shown very good performance and are contributing to the high quality of LHC data. During this presentation the main design requirements and the architecture of the LHC pixel detectors will be presented. We will compare the three detectors, highlighting the most relevant differences between them and the most relevant performance parameters. Low noise, high efficiency and very good position resolution will be stressed, since these items can affect significantly the quality of the experimental data. As an example, more details will be given concerning the operational experience of the CMS pixel detector. Both, the Atlas and CMS collaborations have started an ambitious pixel development program for the upgraded SLHC detectors, which will have to operate in an even harsher radiation environment and at higher data rates. The upgrade path for both detectors will be briefly described.

Speaker: Dr Danek Kotlinski (Department for Particles and Matter, PSI)

Slides iworid.pdf

124 A study of MAPS radiation hardness

Whilst CCD imagers are replaced by CMOS chips in general consumer applications, there is an increased interest in the use of CMOS-based monolithic active pixel sensors (MAPS) for scientific and medical instrumentation. One of the important features that drives the adoption of this technology is its potential use for direct detection of radiation, which avoids the need for intermediate conversion to light and therefore improves the overall performance. A similar application area is imaging radiation in the MeV range with scintillators where the deposited dose in the imager is significant. This work presents an investigation of useful MAPS lifetime under direct exposure to high-energy photons and charged particles, for a range of pixel configurations. Performance of conventional pixels is compared with that of pixels with a radiation-hard design, which include modified transistor and diode layout design and pixel architectures of increased complexity. Lifetime under direct exposure is obtained from highly accelerated stress tests that enable illumination to very high total radiation doses, and which illustrate worst case scenarios that do not allow for damage annealing and recovery. Mean time to failure and degradation rates at room temperature are obtained by monitoring pixel dark noise and gain degradation as a function of dose. Experimental results show that the conventional pixel design does not provide sufficient lifetime for adequate applications under direct exposure, but that pixels with radiation-hard layout design of diodes, transistors and with adequate reset, can provide a lifetime on the range of 10 MRad. This study indicates that radiation damage is not a barrier in the adoption of CMOS-based imagers, provided that the CMOS design is employing standard radiation hardening procedures.

Speaker: Dr Grigore Moldovan (University of Oxford)

Slides A study of MAPS radiation hardness (Protected)

125 Comparison of a CCD and an APS for Soft X-ray Diffraction

We compare a new Active Pixel Sensor (APS) to a Princeton Instruments PIXIS-XO: 2048B Charge Coupled Device (CCD) used by Diamond Light Source (DLS). Despite CCDs being established in the field of scientific imaging, APS are an innovative technology that offers advantages over CCDs. These include faster readout, higher operational temperature, in-pixel electronics for advanced image processing and cost. The APS employed was the Vanilla sensor designed by the MI3 collaboration and funded by the RCUK’s Basic technology grant Funded by MI3 and RCUK technology grant. This sensor has 520 x 520 pixels, of size 25 microns. The readout can be by either an on-chip digital ADC applied to the multiplexed data from the pixel array, or as analogue data from a region of interest digitised later off-chip. The digital mode can operate a full frame readout of up to 20 Hz, whereas the analogue mode can readout a Region of Interest (ROI) at up to 500 Hz (for a 45 x 45 pixel region). The sensor had been back-thinned to the epitaxial layer by E2V. This was the first time that a back-thinned APS had been demonstrated at a beam line at DLS. A typical synchrotron experiment was repeated using DLS’ standard CCD and the novel APS. Soft X-rays (~700 eV) were used to produce a diffraction pattern from a permalloy sample. The pattern was imaged at a range of integration times. The CCD had to be operated at -55°C whereas the Vanilla was operated over a range from 20°C to -20°C. We show that the APS detector can operate with integration times two orders of magnitude less than the CCD, with the Signal to Noise ratio only reduced from 104 to 103. This novel technique allows the capture of data in real time at up to 500 Hz. The detection efficiency of the APS is shown to be the same as that of the CCD and the response is shown to be linear, with no charge blooming effects at the longest integration times. The experiment has allowed a direct comparison of back thinned APS and CCDs in a real soft x-ray synchrotron experiment.

Speaker: Mr Graeme Stewart (University of Glasgow)

Slides IWoRiD.ppt

15:15 Coffee Break & Group Formation

High Energy Physics & Astronomy: 5 contributions

Convener: Prof. Jens Ludwig (Freiburg University)

126 Changes of the particle detection properties of irradiated silicon microstrip sensors after room and elevated temperature annealing.

The changes of the electrical properties of hadron irradiated silicon detectors take place over several years at room temperature. This annealing can be accelerated or dcelerated by lowering or elevating the temperature at which the sensors are kept. This fact is used by the scientists involved in the development of the silicon sensors for the LHC experiments: elevated temperatures (up to 80 oC) have been used to accelerate the effect of the annehaling to study their performances after several years in the experiments, and low temperatures are actually used to retard the undesired effect of annealing duing the times when the detectors are not operated. The acceleration factors with respect to nominal room temperature (RT = 20oC) have been established monitoring the changes of the capacitance-voltage characteristics (CV) with time at various temperatures. It remains to establish if the acceleration factors are also valid for te reverse current (IR) and the charge collection characteristics (CC(V)), that are more relevant to the operations of silicon sensors in high energy physics experiments. In fact in the experiments, the maximum high temperature evisaged out of operation cannot exceed much the 20oC. It is important to assess the exact amount of expected annealing in view of planning the operation scenario (i.e. the bias voltage and temperature) of the silicon sensors in order to have efficient charge collection and controlled reverse current (responsible for power dissipation). In fact it is well known that substantial reduction of the reverse current (more than 50%) can be achieved by annealing. We show here the comparison of elevated and room temperature annealing of the IR and the CC(V) characteristics of detector irradiated to doses expecte in the future upgrade of the LHC at CERN (sLHC).

Speaker: Dr Gianluigi Casse (University of Liverpool)

Slides gcasse.pptx

127 The Belle II pixel vertex detector

Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8x10³⁵cm^-2s^-1 luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. The physical goals of the planned Belle II experiment require a vertex detector with unprecedented performance. The main issues are a high spatial resolution of a few micrometers, a high granularity, and a fast readout speed to cope with the expected high hit occupancy. A new vertex detector (PXD) based on DEPFET technology is being developed, using sensors thinned down to 75um. In the DEPFET pixel concept, the first amplifying transistor is integrated into a high resistivity silicon substrate. By sidewards depletion and an additional n-implantation below the FET, a potential minimum for electrons is created right underneath the transistor channel, which can be considered as an internal gate of the FET. The signal electrons created by an impinging particle are collected and stored in the internal gate, which results in a modulation of the transistor current. The operation mode is the continuous row wise readout (rolling shutter), with four rows read in parallel on each side reaching a readout time of 20 us for a whole frame. The row control is provided by the steering chips (called Switchers) placed in the lateral balcony, while the analog front-end (DCD or Drain Current Digitizer) and the processors (DHP or Data Handling Processor) are on the ends of the stave, on both sides of the ladder. All ASICs will be directly bump-bonded on to the ladder with a dedicated machinery. PXD consists of two layers, at radius of 14mm and 22mm, respectively. The inner layer uses 8, the outer layer 12 individual detector modules. The talk will cover the current status of the PXD system and overview of recent results on system performance.

Speaker: Dr Sergey Furletov (University of Bonn)

Slides iworid-2011.pdf

128 Test results from the NA62 Gigatracker prototype: a high rate and sub-ns time resolution hybrid silicon pixel detector

The NA62 experiment is aimed at studying ultra-rare kaon decays at the CERN SPS, and its beam spectrometer has to sustain high and non-uniform particle rate (0.8-1.0 GHz in total). Three Gigatracker (GTK) stations will precisely measure momentum and angles for each track of the high intensity NA62 hadron beam, with a time resolution of 150 ps. In order to keep background events at acceptable levels, multiple scattering and hadronic interactions of beam particles in the spectrometer have to be minimized. Therefore the total material budget of a single GTK station is fixed to 0.5% X0. In addition, the calculated fluence for 100 days of running is 2 × 10^14 1 MeV neq/cm^2, a comparable value to the one expected in the inner trackers of LHC detectors during 10 years of operation. To comply with these tight requirements, an efficient and low-mass cooling system is being developed and the read-out chips will be thinned down to 100 microns or less. Specifications of this detector are very challenging, especially the one on time resolution. The main issues that have been addressed in order to achieve the required resolution are compensation of the discriminator time-walk and time measurement with such a high channel density. Two complementary read-out architectures have been designed and produced as small-scale prototypes: one is based on the use of a Time-over-Threshold circuit followed by a TDC shared by a group of pixels, while the other makes use of a constant-fraction discriminator followed by an on-pixel TDC. The readout pixel ASICs are produced in 130 nm IBM CMOS technology and bump-bonded to 200 micron thick silicon sensors. Recent experimental results obtained from laboratory and beam tests of prototype bump-bonded assemblies are presented, in addition to a general description of the Gigatracker detector system. These results show a time resolution of less than 200 ps for single hits from minimum ionizing particles.

Speaker: Massimiliano Fiorini (CERN)

Slides Fiorini-iWoRID2011.pdf

129 Monolithic Radiation Image Detectors with SOI technology

We have been developing monolithic radiation detectors based on OKI Semiconductor Co. Ltd. 0.2 µm Fully-Depleted Silicon-on-Insulator (FD-SOI) CMOS technology. The SOI wafer is composed of a thick high-resistivity substrate (for sensor part) and a thin low-resistivity Si layer (for CMOS circuitry) sandwiching a buried oxide (BOX) layer. After removing the top Si and the BOX layer in the region of the sensing nodes, p or n dopant is implanted to the substrate. In the SOI detector, there is no mechanical bump bonds, so the capacitance of the sensing node is very small and has very high sensitivity. Many kinds of detectors are being developed for applications such as X-ray imaging, astrophysics and high-energy physics experiments. In addition to simple integration type detector, we have also developing counting type pixel to utilize the SOI advantage. Largest chip we developed so far is 10.2 mm by 15.4 mm in size having 512 x 832 pixels, each 17 µm square and including correlated double sampling (CDS) function. A new implantation process which creates buried p-well (BPW) layer under the BOX layer is introduced to circumvent the back gate voltage problem inherent in the SOI radiation sensor. There are other benefits in the BPW process such as increase of break down voltage and radiation hardness. Recently we have succeeded to process Floating-Zone (FZ) SOI wafer instead of normal CZ-SOI wafer by adjusting thermal load. The FZ-SOI wafer has higher resistivity (>10 kohm-cm) compared with CZ-SOI wafer, so we could easily achieve full depletion of thick sensor (> 260um) without breakdown. We have been operating regular MPW runs of the SOI process two times per year. Many institutes including foreign institutes are participating the MPW run each time. Recent progress of the SOI detectors will be reported.

Speaker: Prof. Yasuo Arai (Institute of Particle and Nuclear Studies, High Energy Accelerator Research Org. (KEK))

Slides 110706_iWoRID_arai.pdf

130 Readout electronics for the CMS pixel detector upgrade

Commissioning and start-up of the LHC at CERN advances very well. It is expected that the accelerator reaches its design luminosity in the run period starting after 2014 and will go well below that before 2018. In order to exploit the full physics potential even in this very high track density environment, the CMS pixel detector will be replaced by a low mass pixel detector with an additional barrel layer and an additional end disk on each side. However, the detector services cannot be replaced. As a consequence a higher number of modules needs to be powered through the existing cables and a much higher data volume has to be read out through the same number of optical fibers. For this reason new, faster readout electronics and a new powering scheme have to be developed.

Speaker: Dr Hans-Christian Kaestli (Paul Scherrer Institut)

Slides Kaestli_CMS_Pixels.pdf

17:25 PSI guided tour

PSI hosts large facilities such as Proton accelerator, Synchrotron Light Source (SLS), Neutron Spallation Source and soon the Free Electron Laser (swiss FEL). Guided tours to SLS and SINQ are offered.

19:30 Conference Dinner

Conference Dinner at PSI

21:59 Bus Transfer to Zurich

Thursday, 7 July

Applications III: 4 contributions

Convener: Prof. Sture Petersson (Mid Sweden University)

131 Phase sensitive mammographic imaging at the SYRMEP beamline

The phase sensitive imaging methods can be assigned to one of three broad categories namely, x-ray interferometry, diffraction-enhanced imaging (DEI), and in-line phase-contrast imaging (PhC). Using these techniques the gradient or the Laplacian of the x-ray phase is acquired and therefore the density variation and interfaces are emphasized. Phase maps can be obtained by some methods. Soft tissue imaging is very challenging in x-ray radiology as mammography that is an essential tool for breast cancer diagnosis. Therefore improving mammography image quality can have a significant impact on early cancer detection. In medical imaging large field of view and short acquisition time are necessary, moreover phase sensitive techniques require high degree of beam coherence. Considering these constrains the synchrotron radiation (SR) sources are the best choice for these studies. At the SYRMEP beamline of Elettra, the SR laboratory in Trieste (Italy) both phase-contrast and DEI techniques are studied. The application in the field of breast imaging has been carefully evaluated and the first PhC mammography clinical study was performed. We are using different detectors, screen-film system, CCD, photostimulable phosphor imaging plate (IP), silicon pixel detector and we have verified that PhC and DEI techniques have different constrains about detector performance. In PhC imaging, contrast is generated from the interference among parts of the wave fronts that have experienced different phase shifts and it helps to improve the visibility of the borders of structures. In our experience to detect the edge enhancement, the spatial resolution has to be better than 100 micron. In our clinical studies we used both a mammographic screen-film system and a high resolution IP system suitable for clinical mammography. More than 70 patients underwent to SR PhC mammography at our beamline. The DEI technique permits less stringent requirements on the spatial resolution and in the meantime it allows to obtain a set of images with different contrast of the same sample, increasing the amount of information about the sample composition. Very exciting results in the field of phase sensitive imaging have been obtained with the PICASSO detector, a silicon microstrip system (50 micron strip pitch) working in single photon counting mode (using Mythen II ASICs) and used in “edge-on” geometry, under development by our group.

Speaker: Prof. Renata Longo (Università di Trieste - Dipartimento di Fisica)

Slides 01-ForUploadLongo_light.ppt

132 A Fast Neutron Scintillation Detector in Homeland Security Applications

A neutron scintillation detector based on high-pressure He-4 has been developed and demonstrates excellent response to elastic scattering of fast neutrons. The detector removes the need for moderation allowing the preservation of neutron spectral information. Neutrons from three different sources, AmBe, Cf-252, and from the ambient background, have been measured with clearly distinct energy spectra. Exposing the detector to different levels of gamma radiation up to 1 mSv/h from a Co-60 source has demonstrated that gamma exposure does not affect neutron detection performance within measurement statistics. Presented simulations and measurements show that even for shielded neutron sources, a finite number of fast neutrons punch through shielding without undergoing scattering processes. Since fast neutron detectors can reject background neutrons on the basis of spectral information, the detection of only a small number of neutrons can rapidly provide a significant signal relative to all backgrounds allowing the detection of even weak sources. Furthermore, fast neutron detectors can distinguish industrial neutron sources, such as AmBe, from potentially critical fission sources, such as Pu-239, allowing responders to take appropriate threat adapted procedures. Preliminary results of the detectors imaging capabilities for source localization are presented.

Speaker: Dr Giovanna Davatz (Arktis Radiation Detectors Ltd)

Slides ID_160

133 Detection of explosive materials with Gamma Resonant Nuclear Absorption and Argon-Nitrogen TPC

Detection of explosives in large cargo containers is an important preventive measure to counteract terrorism. The element-sensitive radiography with gamma-rays is one promising method, allowing to selectively detect Nitrogen content in various materials, which is a reliable signature of most of commercial explosives. A novel high-resolution tracking detector sensitive to 9.17 MeV Nitrogen nuclear resonant absorption-line is being developed at the University of Bern. The detector is based on a Time Projection Chamber (TPC) filled with a mixture of liquefied Argon and Nitrogen. The facility to generate gamma-rays of the required energy is based on a 2 MeV proton LINAC. First promising results of the performance of the detector and of the gamma-source facility are presented.

Speaker: Dr Igor Kreslo (LHEP, Uni-Bern)

Slides IworiD2011_Kreslo.ppt

134 An electronic detector to replace film for Electron Cryomicroscopy?

Electron cryomicroscopy (cryoEM) is of immense importance in macro-molecular structural determination to as near atomic resolution as possible. Some recently reported structures using cryo-EM have reached 0.33 nm resolution, similar to what can be obtained with X-ray crystallography. A great deal of high resolution cryoEM data is still collected on film, which has excellent resolution, adequate size and high efficiency. A major drawback of film as a recording medium is that, since data is available only after laborious film processing, it would be extremely desirable to switch to an on-line electronic detector with immediate feedback. Although CCD detectors have been in use since the 1990s they do not provide adequate spatial resolution for the most demanding applications, namely single particle analysis of individual biological molecules, with images recorded at 200 – 300 keV. Using experience gained from earlier detectors, we present the design of a detector based on CMOS technology. Since electrons are detected directly, without going through an intermediate light conversion process as in CCDs, the resolution is expected to be superior. The detector, called Falcon, was designed to have a radiation-hard layout to withstand several years of normal cryoEM usage; it contains 4k x 4k (16 million) 14 µm pixels with an input area of 6 cms square, a fast readout and excellent detective quantum efficiency. The detector possesses most of the desirable properties needed for use in cryoEM (and indeed in other fields where electron microscopy is used). A commercial version of this detector has already been produced by the FEI Company, Eindhoven. We will discuss the results obtained at a range of electron energies between 80 and 300 keV, possibilities for biological applications and potential for further technical improvements.

Speaker: Dr Wasi Faruqi (MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, U.K./Institute for Experimental and Applied Physics, CTU in Prague, Prague 2, Czeck Republic.)

135 Direct detection, high frame rate, radiation-hard CMOS monolithic pixels for high resolution Transmission Electron Microscopy

CMOS monolithic active pixel sensors are rapidly becoming an established technology for digital imaging in Transmission Electron Microscopy. Direct electron detection, with sensitivity down to single electrons, benefits the sensor Detective Quantum Efficiency (DQE), while Modulation Transfer Function (MTF) and ultimately single point resolution are greatly enhanced by the thin sensitive layer and the small pixel dimensions achievable with deep-submicron feature size fabrication processes. It has also been demonstrated that sub-pixel resolution can be achieved by creating images from the digital superimposition of single electron hit positions, reconstructed by clustering and centroiding algorithms. Moreover, readout rates of several hundred frames per second (fps) are possible even for large area (megapixel scale) sensors. Over the past year, and benefiting from the earlier LBNL development driven by the TEAM (Transmission Electron Aberration-corrected Microscope) project, we have developed a 16 megapixel, reticle scale CMOS imager optimized for 400 fps readout. The sensor is manufactured in a 0.18 µm commercial CMOS process, and implements pixels of 5 µm pitch featuring an advanced radiation tolerant layout which has been shown to be functional after 300 keV electron doses close to 100 Mrad, ensuring a long device lifetime. The sensor can be used both as an integrating device or as an electron counting device, and is currently being implemented in a commercial digital camera system. The presentation will review this development, and report on the sensor detection and imaging performance, characterized in microscope columns with electrons of energies in the range of interest to TEM (80-300 keV), both under low dose illumination (i.e. single electrons) and high contrast imaging conditions. Further, a prototype chip implementing several novel pixel architectures and layout options will be introduced and evaluated comparatively, e.g. in terms of radiation hardness, in order to identify the best option for the next generation of electron imagers.

Speaker: Devis Contarato (Lawrence Berkeley National Laboratory)

10:25 Coffee Break

Detector Systems II: 5 contributions

136 Characterization of M-π-N CdTe Pixel Detectors Coupled to Hexitec Readout Chip

atterning or pixelization of anode-side of an M-π-n CdTe diode, where the pn-junction is diffused into the detector bulk, is highly motivated to improve the spatial and energy resolution by reading out the electrons instead of holes; to reduce the effects of polarization, and to be able to fabricate double sided M-π-n CdTe detector. It has been shown that very high inter-pixel resistance and low leakage currents are obtained by physical isolation of the pixels of M-π-n CdTe detectors. For this presentation we have patterned M-π-n CdTe detectors to stud bonded them at RAL to a spectroscopic readout chip, Hexitec. The CdTe pixel detectors have 250 μm pixel pitch and area of 5x5 mm2 with thicknesses of 0.5, 1 and 2 mm. The presentation aims to present polarization and energy resolution dependence of the M-π-n CdTe detectors as a function of detector thickness, bias voltage and temperature. The first results with the 1 mm thick Hexitec CdTe detector indicate no obvious polarization at 600 V reverse bias at room temperature when exposed to a Tb fluorescence source (Kα - 44.5 keV) for 2 hours. A single pixel energy resolution at best has been demonstrated to be of the order of 700 eV defined by observed separation of the Kα1 and Kα2 lines of the Tb fluorescence source.

Speaker: Dr Juha Kalliopuska (Microsystems and Nanoanalysis, VTT)

Slides Talk_Kalliopuska_iworid.pptx

137 Development of a fast read-out system of a single photon counting detector for mammography with synchrotron radiation

Purpose: One of the aims of the PICASSO (Phase Imaging for Clinical Application with Silicon detector and Synchrotron radiatiOn) project of INFN-Trieste is to develop a fast data acquisition system for a single photon counting silicon micro-strip detector. The PICASSO detector is designed in order to conform to the needs of imaging large in-vivo samples like breast in the case of mammography. The detector is expected to be fast, and with high efficiency with an aim of delivering a reasonably low dose at high spatial and contrast resolution. Materials and Methods: The current PICASSO prototype comprises two layers of linear array of silicon microstrip sensors of 50 μm strip pitch, 300 μm sensor thickness, and 15mm depth. One layer has three modules, all coupled with MYTHEN II ASIC developed at PSI. Each strip is wire-bonded to MYTHEN II (total 4224 strips and 33 chips per module). PICASSO operates on single-photon counting mode with an “edge-on” configuration. The detector is linked to Picasso Control System, a printed circuit board which is based on an embedded Linux system (ELS). The ELS controls two FPGAs operating the detector with firmware so developed in order to perform fast and real time acquisition. The embedded Linux communicates with a client PC through a server-client architecture via TCP/IP over a standard 100Mbit Ethernet network. Results: The new PICASSO electronics was tested at the SYRMEP beamline of Elettra on January and March 2011. Since both the detector and the beam have a laminar geometry, images are acquired by scanning the sample. Using PICASSO we obtained a frame rate up to 32 Hz at a 24-bit dynamic range. Mammographic test object images were acquired in order to study the effect on the spatial resolution of two different acquisition modalities: either continuous or step mode, within a range of scan steps. Using 100 m scan step significant effect in spatial resolution due to continuous scan, was noted at spatial frequencies higher than 4.5 lp/mm. Conclusion: The detector has shown feasibility of a novel system that can be used for large in-vivo sample imaging. The first results with the new electronics suggest that it may be reasonably used for mammography. With further optimization, frame rate may still be increased by lowering the dynamic range, setting it to 16-bit for instance without a significant change with the hardware. PICASSO is in advanced realization phase: the measurements at SYRMEP are promising and clinical tests are foreseen.

Speaker: Ms Frances Caroline Lopez (Physics Department University of Trieste and INFN-Trieste, Italy)

138 Fast X-ray pixel detectors for synchrotron radiation light sources

This work focuses on the development of fast Charge-Coupled Devices (CCD) for X-ray detection at synchrotron radiation light sources. The presentation will first review the sensor and readout ASIC development that led to the construction of the LBNL Fast CCD (FCCD) and compact FCCD (cFCCD) camera systems, which have been successfully employed in experiments at the LBNL Advanced Light Source (ALS), the ANL Advanced Photon Source (APS) and at the SLAC Linac Coherent Light Source (LCLS). The (c)FCCD is based on a custom, multiport, fully-depleted CCD featuring 480×480 pixels of 30 µm pitch. The sensor has demonstrated excellent single photon sensitivity, high energy resolution and sub-pixel point spread function. The sensor back-plane is processed to allow back-illumination with sensitivity down to few hundred eV X-rays. A custom-designed readout IC provides fast digitization and enables readout at frame rates up to 200 fps. Stemming from the FCCD development, a 1k Frame Store CCD camera system is presently being commissioned, capable of reading a matrix of 1920×960 pixels at 100 fps, or to acquire a 960×960 pixel image at 200 fps in frame store mode. A dedicated DAQ system, based on Advanced Telecommunication Computing Architecture (ATCA), including integrated data processing and compression and capable of streaming to disk the large data bandwidth, will be introduced. Further, the presentation will report on current R&D efforts aimed at the development of X-ray imaging systems for next generation light sources, with target frame rates of order 1000-10000 fps. The design of a fully column-parallel fast CCD and of the ancillary 65 nm CMOS readout ASIC will be presented. As the data volume generated by these sensors will be too large to be streamed to disk in its raw format, work is on-going on modeling the camera system and studying compression algorithms that can reduce the data volume without loss of information. Results from these simulation studies will be reported. Finally, progress on the R&D on thin windows for enhanced soft X-rays sensitivity will be reviewed, and results obtained from both in-house and commercial sensor back-plane processes will be highlighted.

Speaker: Dr Devis Contarato (Lawrence Berkeley National Laboratory)

139 Matching detector performance to source profile to optimise detector linearity

A single photon counting hybrid detector is investigated, especially with respect to linearity, maximum counting rate and dead time. These characteristics are crucial for advanced new detectors for any application and find ideal application in high-performance synchrotrons. We show that the matching of the detector response function with the temporal source structure leads to dramatic improvements in efficiency, count rate and linearity. Results are of wide application. In particular, the approach can be applied to sources used for high-accuracy fundamental experiments including Electron Beam Ion Traps (EBIT) and characteristic calibration sources.

Speaker: Dr Bryn Sobott (The University of Melbourne)

140 Multi-slice Quantum Computed Tomography System using a MHSP

A Computed Tomography (CT) system with multi-slice capability based on a MicroPatterned Gaseous Detector (MPGD) is proposed for small animal imaging and envisaging mammography. This system, with energy discrimination, allows selecting energy windows for the image reconstruction and visualization. Energy weighting is also possible and lead to the enhancement of Signal to Noise Ratio (SNR) and image contrast [1]. MPGDs are excellent in single photon detection, the possibility to set a threshold to eliminate the electronic noise, good energy resolution and fair count rate capability. This system is based on the third generation of CT scanners using a MicroHole and Strip Plate (MHSP) gas detector filled with Xe. The MHSP is an hybrid microstructure with two charge multiplication stages, allowing charge multiplication above 104 and with 2D intrinsic position discrimination capability [2]. This system provides multi-slice acquisition. A cylinder CT phantom made of Poly(methyl methacrylate) (PMMA) with two holes with 2mm and 4mm of diameter was build. Various combinations of material were made to insert in the holes of the phantom to acquire cross-sectional images. Cross-sectional images of biological samples and 3D images of the studied objects will be presented together with a discussion of the future work. References [1]- L.F.N.D. Carramate, et al, “Energy weighting technique in Quantum Computed Tomography using a MPGD” 2011 JINST 6 C02002 [2]- H. Natal da Luz, et al, "Single photon counting x-ray imaging system using a MicroHole and Strip Plate", Transactions on Nuclear Science NS-55(2008) 2341-2345. Acknowledgements: This work was partially supported by project CERN/FP/109283/2009 and FEDER and FCT (Lisbon) programs.

Speaker: Lara Carramate (I3N, Physics Department, University of Aveiro)

141 Summary & Closing

Speaker: Dr Wasi Faruqi (MRC Laboratory of Molecular Biology)