Course on Unfolding of Bonner Sphere Spectrometer Neutron Measurements

26 Jul 2022, 08:30 → 29 Jul 2022, 13:00 Europe/Zurich

Bildungszentrum OSGA/EG06 (Paul Scherrer Institut)

Eike Hohmann (Paul Scherrer Institut)

 

Bonner sphere spectrometers (BSS) are widely used for measuring the spectral neutron distribution. The BSS can determine neutron spectra over a wide energy range covering up to 12 orders of magnitude and it has been used for the measurement of neutron spectra at many different types of facilities, such as reactors, accelerators, and medical facilities. The analysis of the measured data, however, requires unfolding methods, which have to be used carefully to obtain reliable results.

The course provides an introduction to unfolding for BSS with practical applications.

The emphasis is on unfolding exercises using different measurement scenarios. The course is intended for those who do spectrometry in neutron or mixed neutron/photon fields and need to analyze their data using unfolding procedures.

This course is organized as part of EURADOS. 
The main part of the course is carried out by Marcel Reginatto (PTB), Eike Hohmann (PSI) abd Veronique Lacoste (IRSN) with additional contributions from members of EURADOS WG11.

 

The course is a four-day training course on neutron spectra unfolding measured with Bonner sphere spectrometers (BSS), organised by the department for radiation safety and security of the Paul Scherrer Institut (PSI) in collaboration with the neutron radiation department of the Physikalisch-Technische Bundesanstalt (PTB) and EURADOS.

The emphasis of the course is on practical aspects. The course is intended for those who do neutron spectrometry with  BSS in neutron or mixed neutron/photon fields and need to analyze their data using unfolding procedures.

In the morning sessions, there will be a series of lectures which will provide an introduction to unfolding as well as allow for discussions on the theory of unfolding. In the afternoon sessions, the participants will work on specific examples using two methods: MAXED and GRAVEL (See download section for references and additional information). There will also be an introduction to the use of a Bayesian approach for analyzing BSS data.

The course will take place at the PSI Campus with a maximum of 20 participants.  Depending on the current pandemic situation, a change to an online training course may be possible – a hybrid event is not being planned.

Tuesday, 26 July

1 Check-in

2 1. Introduction to unfolding

a. What is unfolding and why is it difficult?
b. Conceptual issues, mathematical issues
c. Some examples of unfolding for particle detectors
d. Review of different approaches to the problem of unfolding

Speaker: Dr Marcel Reginatto (PTB)

3 2. Bonner spheres I

Basic principles, neutron thermal counters, experimental aspects, standard and extended range Bonner sphere spectrometers, etc.

Speaker: Dr Neil Roberts (NPL)

10:30 Coffee Break

4 The role of prior information in unfolding Bonner sphere data

a. Why is it important?
b. Types of prior information
c. How to incorporate prior information into unfolding methods
d. Some statistics relevant to the topic (counting statistics,
chi-squared, etc.)
e. How to choose initial estimates of spectra, etc. Sensitivity
analysis

Speaker: Dr Marcel Reginatto (PTB)

11:50 Lunch Break

5 Installation of the unfolding programs and of the Bayesian program

Speakers: Dr Marcel Reginatto, Dr Eike Hohmann, Dr Benjamin Lutz

15:00 Coffee Break

6 Simple preliminary exercises (to be determined, perhaps measurements at a reactor)

a. Description of the experimental set-ups
b. What problems may one encounter with the examples?
c. Real or simulated data to be used for the unfolding

Speakers: Dr Marcel Reginatto (PTB), Dr Eike Hohmann, Dr Benjamin Lutz

Wednesday, 27 July

7 Validation of Bonner sphere response functions with sources and mono-energetic beams.

Speaker: Dr Neil Roberts (NPL)

8 Review of unfolding methods, part I

a. Why direct inversion fails
b. Direct inversion and “fix it” approaches
c. Regularization methods
d. Linear least-square methods
e. Iterative methods
f. Other approaches: Stochastic methods, neural networks,
etc.

Speaker: Dr Marcel Reginatto (PTB)

10:30 Coffee Break

9 Review of unfolding methods, part II

a. Maximum entropy unfolding
b. Bayesian Parameter estimation and uncertainties

Speaker: Dr Marcel Reginatto (PTB)

11:50 Lunch Break

10 Some relatively simple Bonner sphere unfolding problems (to be determined, perhaps measurements at an accelerator behind shielding)

a. Description of the experimental set-ups
b. What problems may one encounter with the examples?
c. Real or simulated data to be used for the unfolding

Speakers: Dr Marcel Reginatto (PTB), Dr Eike Hohmann (Paul Scherrer Institut), Dr Benjamin Lutz

15:00 Coffee Break

11 Some relatively simple Bonner sphere unfolding problems (to be determined, perhaps measurements at an accelerator behind shielding)

Speakers: Dr Marcel Reginatto (PTB), Dr Eike Hohmann (Paul Scherrer Institut), Dr Benjamin Lutz

Thursday, 28 July

12 Special topics: Bonner spheres II: Calculation of the response function with Monte Carlo codes, problem of the cross sections at high energy

1. Bonner spheres II: Calculation of the response function with Monte Carlo codes, problem of the cross sections at high energy

2. Measurement of cosmic ray induced neutrons

Speaker: Dr Vladimir Mares

10:30 Coffee Break

13 Typical neutron spectra of workplace fields, review of existing reference facilities

a. Reference fields (sources, monoenergetic beams, high
energy quasi-monoenergetic beams)
b. Workplace and other fields (to be determined)

Speaker: Dr Neil Roberts (NPL)

12:00 Lunch Break

14 Approaches to the unfolding of Bonner sphere measurements for the validation of Monte Carlo simulations, focusing on the special case of Bonner sphere measurements at proton therapy facilities

a. Description of the experimental set-ups
b. What problems may one encounter with the examples?
c. Real or simulated data to be used for the unfolding

Speakers: Dr Marcel Reginatto (PTB), Dr Eike Hohmann, Dr Benjamin Lutz

15:00 Coffee Break

15 A Bayesian analysis of one of these examples

A Bayesian analysis of one of these examples

Speakers: Dr Marcel Reginatto (PTB), Dr Eike Hohmann, Dr Benjamin Lutz

18:00 Workshop Dinner

Friday, 29 July

16 Special topics: Facilities representing the new generation of particle acceleration technology (high power lasers, free electron lasers), other facilities

Facilities representing the new generation of particle acceleration technology (high power lasers, free electron lasers), other facilities

Speaker: Dr Veronika Olšovcová,

17 Dead time correction, pulsed neutrons, etc.

Speaker: Prof. Marco Caresana

10:30 Coffee Break

18 Questions from the participants and further discussion with experts about topics of interest, feedback from the participants, closing of the course

Speaker: All lecturers

Visit of a facility

Convener: Eike Hohmann (Paul Scherrer Institut)