ATMOSPHERIC ABSORPTION OF 2.62 MEV GAMMA-RAY PHOTONS EMITTED FROM GROUND

The actual measured decrease in gamma radiation with altitude, as measured by a gamma-ray spectrometer, was found to be less than predicted on simple theoretical grounds. The various factors which reduced this apparent absorption were Compton scattering in the ground and in the air, the variation of detector efficiency with angle, the mass of material of the aircraft structure and detector housing below the detectors, the dead-time of the electronic circuity, and an increase in ground radioactive concentration with depth. When these effects were incorporated, experimental and theoretical values of the linear absorption coefficient in air for 2. 62 MeV photons were found to agree.