SKIN DOSE CALCULATIONS FOR URANIUM FUEL-PARTICLES BELOW 500-MU-M IN DIAMETER

Two different methods for skin dose calculations, VARSKIN Mod 2 and PS S are compared for a spherical uranium fuel particle (diameter 1-500 m u m) deposited on the skin. Nuclide specific beta dose rate at differe nt skin depths for a particle of unit activity is determined as a func tion of particle size. Both methods show that the effects of self-shie lding must be included in the dose calculations for low and medium ene rgy beta emitters. Skin dose rate is drastically overestimated when po int source approximation is used. For high energy beta emitters (e.g., Y-90, Rh-106, and Pr-144) the volume source can be approximated as a point source. The difference in doses is then below 20% for particles up to 100 mu m in diameter. The models give equal results deep in the skin (in terms of range of the beta particles). The reason is that the correction due to the diminished backscattering in air-tissue interfa ce is insignificant at large distances. For three-dimensional sources the backscattering correction should be introduced in the VARSKIN Mod 2.