Skin dose equivalent measurement from neutron-deficient isotopes

Neutron-deficient isotopes decay via positron emission and/or electron capture often followed by x-ray, gamma-ray, and 0.511-MeV photons from positron annihilation. For cases of significant area and/or personnel contamination with these isotopes, determination of skin dose equivalent (SDE) is required by 10 CFR 835. For assessment of SDE, we evaluated the MICROSPEC-2(TM) system manufactured by Bubble Technology Industries of Canada, which uses three different probes for dose measurement. We used two probes: 1) the X-probe, which measures lower energy (4-120 keV) photon energy distributions and determines deep dose equivalent, SDE, and dose equivalent to eyes; and 2) the B-probe, which measures electron (positron) energy distributions and determines skin dose equivalent. Also, the measured photon and beta spectra can be used to identify radioactive isotopes in the contaminated area. Measurements with several neutron-deficient sources showed this system provided reasonably accurate SDE rate measurements when compared with calculated benchmark SDE rates with an average percent difference of 40%. Variations were expected because of differences between the assumed geometries used by MICROSPEC-2 and the calculations when compared to measurement conditions.