Scattering laws and cross sections for moderators and structure materials for calculation of production and transport of cold and ultracold neutrons

Abstract

For calculation of generation and transport of cold and ultracold neutrons scattering law data for gaseous, liquid and solid H2 and D2 as well as for liquid He and some structure materials were derived and applied for transport calculations. The data format of generated scattering laws is ENDF-6. The transport calculations can be performed by both multigroup programs (SN or Monte Carlo) and with the continuous energy Monte Carlo program MCNP. In case of MCNP the production term of ultra cold neutrons is calculated externally to get sufficient statistical accuracy for UCN transport. Reflection in storage of UCN or in neutron guides is treated by a modified reflection routine. Validation is in progress by comparison of evaluated and measured cross sections and -so far available-calculated and measured neutron spectra and gain factors. © 2014 Atomic Energy Society of Japan.