DEPTH-DOSE DISTRIBUTION FOR FISSION NEUTRON-SPECTRA DEGRADED THROUGH LOW Z SHIELDS

Distributions of dose, dose equivalent and quality factor in depth of a cylindrical phantom for neutron spectra moderated by concrete, polyethylene, water and beryllium are presented. These include fission neutron spectra transmitted through 10, 20, 60 and 100 cm concrete; 5, 10, 20 and 40 cm polyethylene; 10 and 40 cm water; and 2.5, 5, 10 and 20 cm thick Be shields. Although average dose per neutron at 1 cm depth depends on the average energy of the neutron spectrum, percentage depth dose distributions for most of the spectra are almost similar. The spectra degraded by 40 cm water and 40 cm PE stand out from others in giving higher percentage depth doses, also the effective quality factor (QF) values remain nearly constant with depth for these spectra. QF values (1 cm depth) range from 7.6 to 8.7 for the spectra studied. They decrease with depth up to about 15 cm and then remain almost constant. Maximum reduction in their values is obtained for a highly degraded spectrum through a 20 cm thick Be shield. © 1979.