Scattering Kernel Calculations for Liquid Para-Hydrogen Using Ring Polymer Molecular Dynamics
(2020) PHYM01 20201Nuclear physics
Department of Physics
- Abstract
- The European Spallation Source will be a world leading neutron source available for a range of neutron scattering experiments in the scientific community. In order to accurately simulate the production of cold and thermal neutrons, an accurate calculation of the neutron cross section for the moderator materials is needed. The neutron cross sections used in the current simulation models for the liquid para-hydrogen moderator at the European Spallation Source are based on scattering kernels computed in NJOY. The scattering kernel calculations for para-hydrogen in NJOY are based on inputs from work that was carried out in the late 1980’s. These approximations have yielded reasonable results and are therefore commonly used in cold neutron... (More)
- The European Spallation Source will be a world leading neutron source available for a range of neutron scattering experiments in the scientific community. In order to accurately simulate the production of cold and thermal neutrons, an accurate calculation of the neutron cross section for the moderator materials is needed. The neutron cross sections used in the current simulation models for the liquid para-hydrogen moderator at the European Spallation Source are based on scattering kernels computed in NJOY. The scattering kernel calculations for para-hydrogen in NJOY are based on inputs from work that was carried out in the late 1980’s. These approximations have yielded reasonable results and are therefore commonly used in cold neutron simulations. In more recent times, input for scattering kernel calculations has been provided by molecular modelling techniques. The present project investigated the methodology of using such techniques for para-hydrogen, namely quantum molecular dynamics. The method was bench-marked against results of other groups and was shown to give a resulting cross section comparable to experimental data as well as simulation data from other groups. Future work for improvements in the method are also discussed and presented. (Less)
- Popular Abstract
- In this project, computer simulations are used to simulate the movement of liquid hydrogen molecules. The information from these simulations is used to model the interactions of neutrons in the liquid hydrogen. The result of this method can be used to update the input to calculations of the neutron production at the European Spallation Source, ESS.
The ESS is a research facility under construction in Lund. It will produce neutrons which will be used in neutron scattering experiments. These experiments use neutrons to scan a sample and by measuring the neutrons that scatters from it, the structure and properties of the sample can be determined. The characteristic properties of the neutron make neutron scattering experiments interesting... (More) - In this project, computer simulations are used to simulate the movement of liquid hydrogen molecules. The information from these simulations is used to model the interactions of neutrons in the liquid hydrogen. The result of this method can be used to update the input to calculations of the neutron production at the European Spallation Source, ESS.
The ESS is a research facility under construction in Lund. It will produce neutrons which will be used in neutron scattering experiments. These experiments use neutrons to scan a sample and by measuring the neutrons that scatters from it, the structure and properties of the sample can be determined. The characteristic properties of the neutron make neutron scattering experiments interesting as they can be used to study a different range of elements and properties of a material, compared to other scattering techniques such as x- ray and electron scattering. This will make the ESS an important facility for a range of research areas, spanning from material science and bio-medicine to fundamental physics research.
In order to produce high quality neutron scattering experiments, a good understanding of the number of neutrons that are sent to the sample, and what energy they have, is needed. This is calculated from computer models of the neutron production process. These models need to know how the neutrons will interact with the different materials that they pass, from when they are created to when they reach the sample. One important material at the ESS is liquid hydrogen which is used to control the energy of the neutrons. A commonly used model for neutron interactions in liquid hydrogen is from the 1980’s. However, recent experiments indicate that the model could be further improved upon.
In the present thesis, a new method is investigated. This method uses computer simulations of the liquid hydrogen molecules to see how they move in the liquid. These results are then used to calculate the probabilities for the neutron interactions in the material. The results of this method are compared to measurements and simulations by other research groups and show good agreement with these. It is therefore shown that this new method can be implemented in the future models used at the ESS for calculating the neutron energy and numbers. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9008217
- author
- Nordin, Pontus LU
- supervisor
- organization
- course
- PHYM01 20201
- year
- 2020
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Neutron scattering, Para-hydrogen, Scattering kernels, Molecular dynamics, Ring polymer molecular dynamics, ESS
- language
- English
- id
- 9008217
- date added to LUP
- 2020-04-28 08:28:51
- date last changed
- 2020-04-28 08:28:51
@misc{9008217,
abstract = {{The European Spallation Source will be a world leading neutron source available for a range of neutron scattering experiments in the scientific community. In order to accurately simulate the production of cold and thermal neutrons, an accurate calculation of the neutron cross section for the moderator materials is needed. The neutron cross sections used in the current simulation models for the liquid para-hydrogen moderator at the European Spallation Source are based on scattering kernels computed in NJOY. The scattering kernel calculations for para-hydrogen in NJOY are based on inputs from work that was carried out in the late 1980’s. These approximations have yielded reasonable results and are therefore commonly used in cold neutron simulations. In more recent times, input for scattering kernel calculations has been provided by molecular modelling techniques. The present project investigated the methodology of using such techniques for para-hydrogen, namely quantum molecular dynamics. The method was bench-marked against results of other groups and was shown to give a resulting cross section comparable to experimental data as well as simulation data from other groups. Future work for improvements in the method are also discussed and presented.}},
author = {{Nordin, Pontus}},
language = {{eng}},
note = {{Student Paper}},
title = {{Scattering Kernel Calculations for Liquid Para-Hydrogen Using Ring Polymer Molecular Dynamics}},
year = {{2020}},
}