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

External irradiations of pig skin using radioactive sources of less than 60 0 mum in the largest dimension (hot particles) were carried out. The object ive of the study was to determine a threshold for scab induction. Hot parti cles used included fissioned U-235 and activated Tm-170, Yb-175, and Sc-46 with maximum beta-particle energies of similar to1.8 (average), 0.97, 0.47, and 0.35 MeV, respectively. The photon emissions from the fissioned U-235 were about 1 MeV per disintegration. The photon emissions from Sc-46 were 0 .89 and 1.12 MeV, with 100% abundance. Photon emissions from Tm-170 and Yb- 175 were negligible. Responses followed cumulative normal probability distr ibutions; thus, no true thresholds could be determined. Hence, 10% and 50% scab incidence rates (ED10 and ED50, respectively) were determined using pr obit analysis. For dose averaged over 1 cm(2) at a depth of 70 mum, the ED1 0 (and 95% confidence limits) were 5.1 (2.7-7.2) Gy for Sc-46, 1.3 (0.89-1. 8) Gy for Yb-175, 2.8 (1.9-3.5) Gy for Tm-170, 8.5 (5.7-9.8) Gy for on-skin fissioned UC2, and 4.5 (0.9-7.2) GS for off-skin fissioned UC2. The ED50 v alues were 12 (8.8-17) Gy for Sc-46, 6.0 (4.3-9.7) Gy for Yb-175, 5.9 (5.1- 6.7) Gy for Tm-170, 11 (9.9-19) Gy for on-skin fissioned (UC2)-U-235, and 1 1 (6.2-14) Gy for off-skin fissioned (UC2)-U-235.