The Air-Ground Interface Problem for Disk Isotropic Cobalt-60 Sources

The exposure angular distributions above various ring isotropic and disk isotropic ⁶⁰Co sources have been calculated in a constant density air medium and compared to Monte Carlo calculations and experimental data for the same sources located at the interface between air and ground. The effect of the interface for ring sources is found to be very similar to the expected results for point sources. For disk sources, the interface effects on the exposure angular distribution are presented as a ratio which has a simple exponential dependence on the cosine of the angle. The results for a very large disk (infinite plane isotropic source) yield correction factors to the assumption that earth can be treated as condensed air.