Depth dose, dose equivalent and quality factor for leakage neutron spectra from critical assemblies

Abstract

Distributions of absorbed dose, dose equivalent and quality factor in depth of a cylindrical phantom for a wide range of leakage neutron spectra from selected critical assemblies have been calculated. The data are provided for 20 neutron spectra which include highly degraded spectra from Vinća, Viper and 13 cm steel shielded HPRR; and relatively undegraded ones from Godiva, Jezebel and bare HPRR and 252Cf fission neutrons. Neutron spectral dependences of dose, dose equivalent and quality factor are discussed. Values of the quality factor at the surface (1 cm depth) range from 6.7 (for Vinća) to 9.8 (for 13 cm steel shielded HPRR). The latter decreases with depth very rapidly reducing to about 50% of its surface value at 5 cm depth, which is found to be a characteristic of spectra leaking through high Z materials. A critical analysis of the depth dose curves has shown that, although these distributions are strongly dependent on the type of assembly and the nature of the shield, small variations in the composition of a given assembly and thicknesses of shield do not significantly affect them.