Gamma-Ray Energy and Angular Distributions above Fallout

Abstract

Detailed data on the gamma radiation environment in air 3 ft above fallout uniformly distributed on a smooth ground surface were calculated using Monte Carlo techniques. The basic data give the energy and angular distributions of the direct-beam and the scattered photon flux above monoenergetic plane isotropic gamma-ray sources for ten different source energies from 0.10 to 3.5 MeV. For each source energy, the flux arriving at the receiver in each of ten energy intervals between 0.04 and 3.5 MeV and eighteen equal receiver angle intervals between 0° (nadir) and 180° (zenith) was calculated. The dose arriving through each 10-degree interval of receiver angle was also computed. To illustrate their application, the results of the monoenergetic calculations were weighted and combined to obtain energy and angular distribution of the photon flux from fallout of four different ages: 1.12 hr, 23.8 hr, 4.57 days and 9.82 days. Comparisons with measured and previously calculated data, both for actual fallout fields and for simulated infinite plane sources, show favorable agreement.