The alpha-activity on the bronchial airways has been calculated for 222Rn daughter exposures producing observable excess bronchogenic lung cancer in underground miners. The activity distribution of aerosol particles with attached 222Rn daughters on the bronchial tree is truly diffuse because of the short half-life of the daughters and the large number of particles in the ambient aerosol. From the bronchial airway activity and the minor epidemiology, it can be shown that it requires, on average, 4 × 109 stem cells in bronchial epithelium to be hit in order to produce an observed lung cancer. For very high 222Rn daughter exposures of miners, multiply hit cells are highly probable; yet the lung cancer response is lower per unit exposure at high exposures than for mining exposures - near those sustained in the environment probably due to stem cell death. A knowledge of the number of multiply hit cells in miners permits some infererences to be made about the effectiveness of particulate versus diffusely distributed a emitters in the lung, namely, that particulates should root be significantly more effective in lung cancer induction than a diffuse distribution.
©1988Health Physics Society