Investigation of complex moderator materials

The main part of the project is to improve our existing synthetic modelling capability to automatically and reliably generate scattering kernels that both accurately reflect the neutron-hydrogen interactions and avoid the majority of the numerical problems that exist with singularities, unbalanced sum rules and other problems that cause Monte-Carlo programs to fail.

ISIS is a pulsed neutron source and as such can only work if the high-energy neutrons (>MeV) created in the target are moderated down to thermal energies (<eV). This is achieved by scattering the neutrons multiple times off a light nucleus (e.g. hydrogen), where the neutrons slow down (moderate) to the thermal energies of the material.  We have been doing that with simple hydrogenous materials e.g. liquid H2 and water. Importantly, the final spectral distribution of the neutrons is determined by the density of states (chemical properties) of the hydrogen material.

In recent years there has been a dramatic increase in the number of studies on hydrogen storage materials. One class of these materials are the metal oxide frameworks (MOFs), which offer an almost infinite number of structures that can be adapted to store hydrogen and a huge range of local chemical properties. Coupled with the dramatic increase in computational ability and improvements in theoretical understanding of the scattering processes within these complex H2 storage materials, we are now in a position to directly simulate the performance of these materials for use in the ISIS moderators.

In principle, we could take the databases on known MOFs, calculate their likely H2-scattering kernel at liquid

H2 temperatures and perform standard Monte-Carlo simulations to evaluate the moderator performance.  Challenging obstacles stand in the way of this: the synthetic kernel models, that we use to calculate the probabilistic scattering for a single neutron-hydrogen interaction, only work well for certain energy ranges requiring significant case by case optimization; the database of measured data has not been checked against the current models; additional information e.g. NMR, Infra-red etc, has not been used to refine the synthetic models; and no automated process exists.

The project’s objective is to rectify these deficiencies.

List of Duties / Work Programme / Responsibilities

The project has several steps:

1.     Learn how to use NJOY and endf2ace to make scattering kernels for low temperature materials.

2.     Calculations using MCNPX/Geant of a simple moderator/target unit.

3.     Understand our existing C++ code for the synthetic model, and write test-code and develop techniques to avoid problems with the kernels

4.     Write code to help integrate additional data e.g. NMR

5.     Automate as much as possible and determine candidate materials.

The main part of the project is to improve our existing synthetic modelling capability to automatically and reliably generate scattering kernels that both accurately reflect the neutron-hydrogen interactions and avoid the majority of the numerical problems that exist with singularities, unbalanced sum rules and other problems that cause Monte-Carlo programs to fail.

Personal Skills and Attributes

This project is designed to introduce the student to a number of areas of Monte Carlo simulation, numerical analysis, and nuclear transport simulation. The project will contain a large amount of computational software development and should enhance the students computing ability in typical numerical languages e.g. C++/R/F90 and techniques e.g. object orientation, parallel applications, algorithm development etc.

You will be working within the Neutronics Group at ISIS, who will provide the necessary training. The project is designed to introduce the student to these areas

It is essential that the student has programming skills, and is aware of the tool chain in larger software projects, from source code repositories (e.g. git/SVN), build systems (e.g. cmake/scons), debuggers and runtime performance checkers (e.g. valgrind/gprof).

 Contacts and Communication

For further information about the position, please contact Stuart.Ansell@stfc.ac.uk or ISISSandwichStudents@stfc.ac.uk.

Application forms and further details about sandwich student placements at ISIS are available from http://www.isis.stfc.ac.uk/learning/placements/read-more-about-placements-at-isis13306.html. The closing date for applications is 16th November, 2012.

Bookmark and Share
Skip to the top of the page