Organ Doses Due to External Gamma-irradiation Arising from a Finite Plume in the Atmosphere

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Abstract
A procedure was developed for the calculation of absorbed doses to human tissues or organs due to external .gamma.-activity from an atmospheric release of radioisotopes in the form of a finite plume. The procedure was based on the moments method, which yielded a solution of the photon transport equation for infinite air. Analytical expressions were derived which were applied to these infinite air .gamma.-fluxes to allow for the presence of the ground. Photon spectra and exposures was calculated for any type of plume composition, release, height and atmospheric stability. By combining the computed spectra with published human organ doses due to external irradiation, absorbed doses to various human tissues were evaluated. Calculations were also carried out, on the basis of ICRP [International Commission on Radiological Protection] recommendations, to predict effective dose-equivalent and effective dose equivalent per unit exposure (rem/R) factors. As examples of the application of the method in safety assessment, 1 hypothetical monoenergetic emitter release and 1 notional Magnox reactor release were considered. The annihilation radiation contribution to exposure was also discussed.