Alpha Absorption Measurements Applied to Lung Dose from Radon Daughters

Authors:
  • NHN. H. Harley
    N. H. Harley
  • BPB. S. Pasternack
    B. S. Pasternack
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Abstract
In this study, experimental alpha attenuation data were obtained in polycarbonate which is essentially identical to tissue in ionization potential. Alpha transmission and stopping power data were developed for the radon daughters RaA (218Po) and RaC' (214Po). The experimental stopping power measurements were found to be in agreement with values calculated using the Bethe-Bloch equation and the Bragg additivity rule. Experimental alpha attenuation data were also obtained in a gas with the same composition as ICRP tissue and were found to be identical with that in the solid tissue equivalent. The experimental data were then applied to determine the spatial distribution of alpha dose in bronchial epithelium when the alpha activity is present in mucus on the tracheobronchial surfaces. Dose curves as a function of depth into the bronchial epithelium were developed for two different airway diameters. The alpha dose from exposure to radon daughters was computed using the bronchial activities derived by Altshuler for a radon concentration of 100 pCi/l. The new dosimetry yields results which are lower by about 20 %. An independent dose calculation for radon daughters was also performed incorporating more recent data on mine atmospheres. The alpha dose to bronchial epithelium using these factors was found to be considerably lower than any calculated previously for the same radon concentration. A few alpha doses were also computed in terms of working level units. It was shown that the alpha dose for one working level may be widely different depending upon the ratios of the radon daughters.