Threshold levels for nonstochastic skin effects from low-energy discrete radioactive particles

This project addressed the problem of discrete radioactive particles (DRPs) producing nonuniform external radiation exposures because of their small size and low-penetrating radiation. It included a literature review of experimental work performed to determine threshold radiation doses for both stochastic and nonstochastic skin effects. Study objectives included: (1) quantifying the effects of source size, beta particle energy, and mixed field exposures, (2) obtaining experimental data for 3-mm and 11-mm source sizes, and (3) developing and validating a predictive model for nonstochastic effects as a function of energy spectra and source size. Co-60 and Ca-45 disks with 3-mm and 11-mm diameters were used to expose each of three Hanford miniature swine to low-energy beta radiation at discrete locations on the skin. Three observers, using their own evaluation criteria, viewed and rated skin conditions over a period of 20 weeks. A modified version of the computer code, VARSKIN, was used to construct dose profiles for sources used in the new experiments and reconstruct doses for experiments reported in the literature. Data produced provide the technical bases for developing regulations for controlling exposures to DRPs.