On The Use of Beryllium as Thermal Neutron Filter

Abstract

A formula is given which allows to calculate the contribution of the
nuclear capture, thermal diffuse and Bragg scattering cross-section to the
neutron transmission through solid crystalline Beryllium. The formula takes
into account the beryllium crystalline structure and its physical parameters. A
computer program CRYSBE was developed to provide the required calculation.
The calculated values of the total cross-section of polycrystalline beryllium at
different temperatures were compared with the previously measured ones in the
neutron energy range from 0.2 meV to 10 eV . The obtained agreement shows
that the formula fits the experimental data . An agreement was also obtained for
values of beryllium single crystal at both room and liquid nitrogen
temperatures. The feasibility study on using a polycrystalline beryllium as a
cold neutron filter is given. The optimum beryllium single crystal thickness,
mosaic spread, temperature and cutting plane for efficiently transmitting the
thermal reactor neutrons, while rejecting both fast neutrons and gamma ray
accompanying the thermal ones are also given .