Calculation of neutron scattering libraries for liquid ortho-deuterium and hydrogen deuteride
(2022) FYSM60 20212Nuclear physics
Department of Physics
- Abstract
- The European Spallation Source (ESS) has launched a project called HighNESS, with the task of investigating the potential of adding a second moderator system to the facility, with ortho-deuterium (o-D2) being the main material of interest. Another moderator material which could be of interest is hydrogen deuteride (HD). The purpose of this second moderator system would be to provide a high intensity source of neutrons, compared to the high brightness of the first moderator system, as well as providing a colder neutron spectrum.
In order to accurately simulate the low-energy neutron production from moderators, the thermal scattering law (TSL) of the materials in question is needed, typically in the form of scattering libraries. Previous... (More) - The European Spallation Source (ESS) has launched a project called HighNESS, with the task of investigating the potential of adding a second moderator system to the facility, with ortho-deuterium (o-D2) being the main material of interest. Another moderator material which could be of interest is hydrogen deuteride (HD). The purpose of this second moderator system would be to provide a high intensity source of neutrons, compared to the high brightness of the first moderator system, as well as providing a colder neutron spectrum.
In order to accurately simulate the low-energy neutron production from moderators, the thermal scattering law (TSL) of the materials in question is needed, typically in the form of scattering libraries. Previous scattering libraries for ortho-deuterium were created based on input derived from experimental data and early theoretical models, and no scattering library exists for hydrogen deuteride. This work used a type of quantum molecular dynamics (QMD), namely ring polymer molecular dynamics (RPMD) to obtain inputs for the NJOY software wherein the scattering libraries and the cross-section were calculated for ortho-deuterium and hydrogen deuteride. Seeing as NJOY was not developed for heterogeneous molecules such as hydrogen deuteride, it had to be extended to include models for such molecules. The quantities from the molecular dynamics simulations and the cross section of both materials were benchmarked against experimental data and simulated data from other research groups. Possible improvements and continuations beyond this work are also discussed and presented in this report. (Less) - Popular Abstract
- The European Spallation Source (ESS) is an international research laboratory which is currently under
construction in Lund, Sweden. Once completed, the ESS will provide the brightest pulsed neutron source
in the world for neutron scattering studies. The ESS will serve a wide range of research fields using
neutron scattering experiments. The neutrons are produced by accelerating protons and firing them at
a tungsten target where the protons will knock out neutrons. The neutrons are then slowed down by a
moderator to reach lower, more useful energies. Afterwards, they are guided to the experiment stations
where they are used in various experiments. A project launched by ESS, called HighNESS, is looking to
expand the array of possible... (More) - The European Spallation Source (ESS) is an international research laboratory which is currently under
construction in Lund, Sweden. Once completed, the ESS will provide the brightest pulsed neutron source
in the world for neutron scattering studies. The ESS will serve a wide range of research fields using
neutron scattering experiments. The neutrons are produced by accelerating protons and firing them at
a tungsten target where the protons will knock out neutrons. The neutrons are then slowed down by a
moderator to reach lower, more useful energies. Afterwards, they are guided to the experiment stations
where they are used in various experiments. A project launched by ESS, called HighNESS, is looking to
expand the array of possible neutron science experiments available at the facility. HighNESS proposes
to do this by installing a second moderator, which would be able to produce a high intensity of neutrons
at lower energies, compared to the first moderator. This would enable experiments in several fields of
research which are currently not possible elsewhere. The choice of material which is going to be used in
the proposed second moderator is currently being researched.
The performance of moderator materials at neutron sources is often characterized through Monte-
Carlo simulations. An important step in this process is the accurate description of the neutron transport
through the material on an atomic and molecular level. This data is collected and stored in a scattering
library. The next step is to simulate the facility setup using a detailed model of the target and moderator
systems, where the scattering library obtained earlier describes how the neutrons will scatter through
the moderator materials. This simulation allows one to calculate how many neutrons could serve the
experimental stations and what energy they will have, which is crucial to know since this relates directly
to the performance of the facility.
The purpose of this thesis has been to generate scattering libraries for two materials, ortho-deuterium
and hydrogen deuteride, both which could be used as a moderator at ESS. While scattering libraries exist
for ortho-deuterium, these libraries use early theoretical models which could be potentially improved
upon by incorporating state-of-the-art molecular dynamics techniques into the model description. The
new scattering library for ortho-deuterium uses methods which account for the quantum behaviour of
the moderator material, through the use of quantum molecular dynamics techniques. The work carried
out for hydrogen deuteride represents the first available scattering library for this material to date.
Quantum molecular dynamics techniques were also used as input to the models for hydrogen deuteride.
The main difference is that the ortho-deuterium molecule has two of the same atomic nuclei, while the
hydrogen deuteride molecule has two different atomic nuclei which makes it more complex in some regards.
The results of the work, on several levels, were compared to experiments and simulations found in the
literature. Good agreement was found where data was available.
This work builds the basis for future design work on moderator systems at the ESS. For example, a
continuation of this project would be to investigate the moderator performance of hydrogen deuteride,
compared to liquid deuterium and liquid hydrogen, through the use of Monte-Carlo simulation. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9073781
@misc{9073781,
abstract = {{The European Spallation Source (ESS) has launched a project called HighNESS, with the task of investigating the potential of adding a second moderator system to the facility, with ortho-deuterium (o-D2) being the main material of interest. Another moderator material which could be of interest is hydrogen deuteride (HD). The purpose of this second moderator system would be to provide a high intensity source of neutrons, compared to the high brightness of the first moderator system, as well as providing a colder neutron spectrum.
In order to accurately simulate the low-energy neutron production from moderators, the thermal scattering law (TSL) of the materials in question is needed, typically in the form of scattering libraries. Previous scattering libraries for ortho-deuterium were created based on input derived from experimental data and early theoretical models, and no scattering library exists for hydrogen deuteride. This work used a type of quantum molecular dynamics (QMD), namely ring polymer molecular dynamics (RPMD) to obtain inputs for the NJOY software wherein the scattering libraries and the cross-section were calculated for ortho-deuterium and hydrogen deuteride. Seeing as NJOY was not developed for heterogeneous molecules such as hydrogen deuteride, it had to be extended to include models for such molecules. The quantities from the molecular dynamics simulations and the cross section of both materials were benchmarked against experimental data and simulated data from other research groups. Possible improvements and continuations beyond this work are also discussed and presented in this report.}},
author = {{Huusko, Alexander}},
language = {{eng}},
note = {{Student Paper}},
title = {{Calculation of neutron scattering libraries for liquid ortho-deuterium and hydrogen deuteride}},
year = {{2022}},
}