On the air-scattering of gamma rays from thick uranium sources

Semiquantative interpretation of data from airborne radioactivity surveying requires detailed knowledge of air-scattered gamma-ray intensity at considerable air distances from natural, thick uranium sources. Based on the concept of an elementary source of infinite
thickness rather than on the classical point source, semi-empirical
expressions, are developed for measured gamma-radiation intensities from
. the two extreme types of natural, thick uranium sources, the elementary
(point) and t-he broad (semi-infinite) source. These expressions agree
both with extensive experimental data and with the form and structure
of theory.

Theoretical computations based on published solutions of the
Boltzmann equation for ga.m.ma-ray transport in one medium agree closely
with experimental measurements. The calculated value for primary,
scattered, and total intensities from thick uranium sources show that
at considerable air distances the scattered intensities are more than
half of the total intensities for energies above 0.4 Mev and become
considerably more than half as the lower limit of detector energy
response is decreased below 0.4 Mev.