Scab diameters on pig skin resulting from hot particle exposures under varying conditions

The National Council on Radiation Protection and Measurements (NCRP) in NCRP Report Number 106 recommended a limit of 10(10) beta particles emitted from radioactive particles with sizes less than 1 mm (hot particles) to prevent acute deep ulceration. This recommendation was determined, in part, by regressing the diameter of the scabs induced by fissioned 235UC2 hot particles as a function of the logarithm of the number of beta particles emitted from the sources for one study. To validate this recommendation and the approach used by the NCRP, external irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension were carried out. The hot particles used included fissioned 235UC2 and activated 170Tm, 175Yb, and 46Sc. Results indicated a strong correlation between scab diameter and dose for scabs induced using fissioned 235UC2, activated 170Tm, and 46Sc, but not for 175Yb. The correlation value decreased with decreasing beta particle energy, with the exception of 46Sc, which had scabs with diameters greater than twice the maximum beta particle range. The larger scabs from 46Sc are thought to be due to dose contributions from the gamma rays. The results also give an ulceration threshold less than that given by NCRP to prevent acute deep ulceration. It was concluded that regression analysis of scab diameter as a function of either number of beta particles emitted from the hot particles or dose did not yield either precise or accurate thresholds but was useful in determining probable ranges of doses which lead to scab induction.