Laboratoire d'accueil : Laboratoire d'expertise et de recherche en neutronique des réacteurs (LNR)
Date de début de thèse : octobre 2015
Nom du doctorant : Vaibhav Jaiswal
Descriptif du sujet
Nuclear cross section libraries use derived thermal neutron scattering represented by
scattering kernel S(α,β) where α and β stand for the unit-less momentum and energy
transfers respectively. The available S(α,β) of light water in the evaluated data libraries
are based on physics models and experimental data measured in the sixties with a low
accuracy due to limitations of the experimental and computational capabilities. S(α,β) is
analogous to the scattering function S(q,ω) which describes the microscopic dynamics
of a scattering system, where q is the neutron momentum transfer and ω is the neutron energy transfer. S(q,ω) for light water can be directly measured by performing time-offlight inelastic thermal neutron scattering experiment in order to avoid approximations and thus possibly enhance the reliability of S(α,β) and accuracy of the thermal scattering cross section.
Improved S(q,ω) and thermal scattering cross section of light water at ambient temperature and pressure have been successfully carried out at Institut Laue-Langevin (ILL). The first part of my work was to extend the previous measurements beyond room temperature and pressure, to more realistic operating conditions in connection with nuclear power reactors. In order to accomplish this, two consecutive inelastic thermal neutron scattering experiments was performed with light water for several high temperatures and pressures using high resolution time-of-flight spectrometers, IN4c and IN6 at ILL in 2015. Data reduction of the raw experimental data to obtain S(q,ω) is under process (Figure). S(q,ω) will then be transformed into S(α,β) to calculate the double differential thermal neutron scattering cross section. The final result will focus on the effect of temperature and pressure on the thermal scattering kernel S(α,β) of light water and its impact on integral experiments.