Radiation shielding of an 8 in x 6 in Nal(TI) crystal for use in keV neutron capture experiments.

Abstract

The sensitivity of large NaI(TI) detectors to background radiation inhibits their use in measuring partial neutron capture cross sections in the keV energy region. Major sources of neutron induced background are the iodine in the crystal and iron in structural materials. In a survey of possible neutron shielding materials, a 70 percent by weight mixture of boron carbide in paraffin most readily reduced keV neutron fluxes. The use of a multi-layered shield assembly, incorporating an inner sleeve of boron carbide and lead shot in a litharge/glycerine cement, gave a factor of 10 improvement in the counts-to-background ratio at the 37 keV resonance in 48Ti.