A STUDY OF THE RELATIONSHIP BETWEEN THE NEUTRON ABSORBED DOSES IN AN UNDERGROUND STRUCTURE AND IN A SEMI-INFINITE MEDIUM

The penetration of neutrons from nuclear weapons into underground structures is studied in idealized fashion. Neutrons from a burst about a kilometer directly overhead are considered incident upon the surface of a semi-infinite medium of concrete-like properties. Calculations of two general cases are made: (1) the absorbed dose within the unperturbed medium at certain depths; and (2) the absorbed doses at various locations in a cylindrical cavity in the medium. Results are expressed as ratios of the second case to the first, thus treating the cavity as a perturbing influence upon the absorbed dose field in the semi-infinite medium. The computer code 05R is adapted to this study. Results indicate that the cavity perturbation ratios are always less than unity, implying the possible use of simple semi-infinite medium calculations as conservative estimates of radiation penetration into underground structures. Generalizations to more practical cases are made. A simple diffusion model approach to calculation of the ratios is shown to be adequate for cavities representing normal rooms, but not vertically long and narrow (silo-like) cavities. (Author) Report on Nuclear Radiation Shielding Studies.