The design of cold neutron filters

Abstract
The problems of designing cold neutron filters are surveyed and discussed. Theoretical expressions for the mean wavelengths and fluxes of the cold neutron beams are given. The choice of filter material is discussed and the physical state of the material is shown to be an important factor. Filters using beryllium, magnesium, magnesium oxide, lead and bismuth have been made and their performances tested and compared with theory.