Angular Dependence of the Components of Dose to the Bone Marrow and Abdomen in a Human Phantom from 2.95-MeV Neutrons

Abstract

Gamma and recoil-ion dose measurements were carried out in a human-shaped phantom exposed to whole-body monoenergetic neutrons at 2.95 MeV. For the gamma component miniature, energy-compensated, thermoluminescent dosimeters of CaF₂: Dy were used inside bones to measure the bone-marrow dose. For abdominal dose and surface dose, a small Geiger chamber was used to supplement the TL system. Proportional counters were used for the recoil-ion measurements. The dose components were measured as a function of both the angle of phantom rotation and the angle of elevation of the incident radiation. The significance of the gamma component of the fast-neutron dose is discussed, and it is shown to be of particular importance with respect to incident neutron energies of 3 MeV and below, to off normal angles of irradiation, and to the low values of the quality factors required for acute effects of radiation dose. Internal recoil-ion dose may be predicted within a factor of two from calculations. The study shows the very large effect due to the angle of incidence of the neutron radiation, and it suggests that the chest is an unsuitable badge location for practical accident dosimetry.