Characteristics of poly- and mono-crystalline BeO and SiO2 as thermal and cold neutron filters

• Neutron filtering features of BeO and SiO2 poly- and mono-crystals.
• Calculations of the cold and thermal neutron cross sections and transmission with the code “HEXA-FILTERS”.
• Optimal mosaic spread, thicknesses and cutting planes for BeO and SiO2 mono-crystals.

A simple model along with a computer code “HEXA-FILTERS” is used to carry out the calculation of the total cross-sections of BeO and SiO2 having poly or mono-crystalline form as a function of neutron wavelength at room (R.T.) and liquid nitrogen (L.N.) temperatures. An overall agreement is indicated between the calculated neutron cross-sections and experimental data.Calculation shows that 25 cm thick of polycrystalline BeO cooled at liquid nitrogen temperature was found to be a good filter for neutron wavelengths longer than 0.46 nm. While, 50 cm of SiO2, with much less transmission, for neutrons with wavelengths longer than 0.85 nm. It was also found that 10 cm of BeO and 15 cm SiO2 thick mono-crystals cut along their (0 0 2) plane, with 0.5° FWHM on mosaic spread and cooled at L.N., are a good thermal neutron filter, with high effect-to-noise ratio.