The practical training takes place at the Paul Scherrer Institut and allows participants to do experiments in groups at the large facilities, such as the spallation neutron source SINQ, the Swiss Muon Source SμS as well as the Swiss Light Source SLS.
The participation fee for the practical training of CHF 170.00 has to be paid cash upon arrival to the School on Saturday, August 11, 2012.
The fee covers the entire practical training, including accommodation for 3 nights (August 17 - 20, 2012) at the PSI Guesthouse (incl. breakfast, lunches and dinners).
Transportation from Zug to PSI on Friday, August 17, 2012 is not included.
The following practical training sessions will be offered:
|Title / Abstract
|SLS - photons
X-Ray Coherent Diffractive Imaging
Coherent diffractive imaging (CDI) is a microscopy technique, in which one does away with image-forming optics by using mathematical algorithms to "reconstruct" the image based on the distribution of scattered light. We will use this method to obtain highly resolved X-ray images of both synthetic test nanostructures and life and materials sciences-related samples. In particular, we will illustrate the workings of the image reconstruction algorithms.
|SLS - photons
MicroXRF/XAS studies on the chemical speciation of nano-particles within planktonic invertebrate species
Daphnia magna represents a well-known and ecologically important planktonic invertebrate species (see Figure 1). Since it is quite sensitive to a wide range of toxicants and plays an important ecological role as the link between the primary producers and secondary consumers, it has been extensively used as an acute and chronic test organism for many regulatory chemicals and is also included in many international standards and guidelines for in vivo ecotoxicity tests. MicroXRF/XAS techniques can be used to obtain chemical speciation information of heteronegeous systems with micron scale resolution. Fluorescence (XRF) mapping offers simultaneous reading of multiple elements present in the sample, while micro-Xray absorption (XAS) reveals the oxidation state of particular atoms in different micron-size spots on the specimen. The spatial distribution and possible biodegradation of colloidal Fe-oxide nanoparticles absorbed by Daphnia Magna will be performed at the microXAS station You will start the practical using conventional two-dimensional scanning fluorescence technique (micro-XRF) to visualize the spatial distribution of Fe-oxide nanoparticles within the D. magna. The X-ray beam will be focused to a size of 3x3 μm, and the scan step will be 2 μm with 0.2 s dwell time per pixel, using a single element Si-detector. The typical size of the fluorescence map is 500x500 μm2. Depending on the experimental conditions (sample concentration and available beamtime), higher resolution micro-XRF images may be also collected over longer period of time. In selected regions of the digestive track, X-ray absorption spectroscopy scans will be conducted at the Fe K edge, in order to probe the potential changes in the oxidation state of the Fe atoms, after exposure to D. magna. These scans will be later compared with the data obtained on the initial Fe-oxide nanoparticle material, before the exposure to the invertebrate organisms. The goal of the experiment is to prove or dismiss the hypothesis of in vivo biodegradation of Fe-oxide nanoparticles inside the Daphnia magna, which can have a significant impact in the area of nanotoxicology.
Scanning soft X-ray microscopy
A major advantage of scanning transmission X-ray microscopy (STXM) is its ability to measure organic materials with high resolution and strong contrast between organic components based on molecular structure. The HERCULES 2012 experiment at the PolLux STXM will involve measuring conjugated polymer blend thin film samples and analyzing the data to produce quantitative composition and thickness maps. With no significant difference between the component polymers in terms of density, elemental composition or isotopic composition, the two materials appear nearly identical in most analytical techniques. In the experiment, we will tune the probing photon energy to near- edge absorption resonances that are associated with promotion of electrons (via photo- absorption) from the C 1s shell into unoccupied anti-bonding molecular orbitals, which are closely associated with the molecular structures, thus providing stron differentiation between the polymers. The conjugated polymer blend film studied is a model system for polymer-based optoelectronic devices such as solar cells and LEDs, but the STXM technique demonstrated is applicable to a broad range of sample materials of interest to subject areas such as chemistry, biology, physics, geology and archaeology.
Grating interferometry for imaging and metrology
A grating interferometer (GI) is a diffractive optical element that is capable of characterizing a beam profile. Mounted between a sample and a detector, it can be used to measure a map of refraction angles induced by the sample. We will use the GI to determine the transversal coherence length (and thus the source width), the most crucial parameter for all modern coherent imaging techniques. In a second step, the GI together with tomography will be used to answer an important question: “Did this mouse suffer from Alzheimer's disease?”
|During the experiments at ICON you will be able to use real-time neutron imaging, neutron tomography, and material characterization using selected neutron energies. In the first task the objective is to tune the imaging system to make a movie with a frame rate of a few images per second with a sufficient image contrast. The process is we will study is boiling water. The second experiment is about the acquisition of a tomography data set followed by the reconstruction and the visualization of the imaged object. In this experiment you can propose a sample, it will however be a low performance CT due to the available time. The last part of the practical relates to the energy response of different materials. By selecting the neutron energy to a narrow band features in the sample appear that would remain hidden in a polychromatic beam. In this experiment some dedicated samples will be provided. After the experiment you will do the data evaluation of the energy scan images.
Objectives - There is a new electronic moisture sensor developed at EMPA. We aim to precisely quantify in a time-resolved manner the two-dimensional moisture content distribution in several porous materials, where our new moisture sensor is embedded. The porous material is initially wetted and the drying occurs at one surface exposed to air. These data are required to compare the sensor output to the actual moisture content.
Experimental procedures - The sensor is embedded in the freshly mixed material and the material is let to dry. The thickness of the sample will be optimized in terms of the neutron imaging but can be in the range of 1 to 2 cm. We propose to document the drying of four different materials: gypsum plaster, cementious interior rendering, plaster rendering with aerogel filler and cementitious floor screed. All samples will be prepared 24 hours before their planned Neutra measurements. This allows for the hydration to be mostly completed and ensures that the porous material is in drying phase. We will image the sample in two sessions of two days each. In the first Neutra session, all samples are initially imaged at 24 hours into the drying stage. Then the top surface of the samples is wetted with 1 ml of water and each sample is imaged during 8 hours.
Expected results - The drying behavior of the four samples will be documented in terms of temperature and moisture content distributions during the eight-hour experiments. Comparison with the sensor outputs will serve first to ascertain the capacity of the sensor to actually measure local moisture contents, and, if so, whether actual moisture content could be assigned via calibrating curves. The recorded data will be further analyzed by comparison with heat and mass modeling results.
About the similarity of an eraser and an aluminium component
Everyone knows this phenomenon: bending an eraser between two fingers often results in two eraser halves. But why is this actually happening?
Responsible for the fracture are tensile stresses close to the upper surface of the eraser caused by straining between fingers. Tensile stresses “pull” on small cracks, resulting in crack growth and propagation, which finally may lead to failure. On the other hand, compressive stresses, which occur at the bottom side of on bended erasers, inhibit crack propagation. In this practical we will study such a stress state from top to bottom surface by neutron diffraction. Since in strain and stress analysis by diffraction methods the lattice spacing of crystal planes act as strain gauge, these methods require a crystalline structure, not given in case of the rubber. Therefore we will investigate this particular stress state in a plastically deformed aluminium bar with the shape of a bended eraser. The nature of diffraction allows not only the determination of stresses but also the distinction between different crystallographic directions. The differences get particularly visible in so-called in-situ tests. In-situ tests combine mechanical tests with diffraction measurements. In that way the response of different crystallographic directions on mechanical load may be studied and compared to each other. Such differences reflect the crystallographic anisotropy of the material, which is important for many processes in production routes of industrial components. In this way we will enlighten the processes leading to the “bended eraser” stress state in the aluminium bar.
Mapping magentic profiles on a nanomenter scale
Low-energy muon spin rotation (LE-μSR) is used to measure the magnetic field inside a material as a function of depth. Changing the muon implantation energy between 1 and 30 keV allows mapping the field profile in a muon stopping range from a few nanometers up to 200 nm, thus obtaining a one-dimensional image of the field below the surface. We will use this technique to directly determine the absolute value of the London magnetic penetration depth λL of high-Tc cuprate superconductors as a function of temperature. λL is a fundamental parameter of each superconductor due to its relation to the superfluid density ns. Knowledge about the dependence of ns on parameters such as temperature, pressure, crystal orientation, is of central importance in testing theories of exotic superconductors.