Screening criteria for skin contamination in a radiological emergency
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In response to a nuclear or radiological emergency, potentially contaminated individuals are screened for external contamination. During the screening process, a threshold screening level is used to triage into two groups: one consisting of those individuals who need to be decontaminated and the other consisting of those who are either uncontaminated or will be given instructions for self-decontamination. Several organizations have suggested generic contamination levels for this threshold. However, differing assumptions made during the development of these values regarding the radionuclides present, the distance between the contaminated surface and the detector, the extent of contamination, the detector type, etc. have led to potential disagreement between the suggested screening values. This study uses a modified PiMAL phantom and an experimentally verified Geiger-Mueller (GM) pancake probe modeled in the MCNP6 (Monte Carlo N-Particle 6) transport code to examine the effects of these differing assumptions on the dose received by a contaminated individual. A 5 micron layer of contamination was modeled to be in direct contact with the epidermis of the phantom. Five sets of models were created. Each set independently varies either the thickness of the epidermis, radionuclides comprising the contamination, distance between the probe and the contamination, extent of contamination, or exposure time. The amount of activity assumed to be present was such that it elicited a detector response of 1000 counts per minute (cpm) for each model. In each scenario, the relationship between the absorbed dose in a 10 cm2 area of the dermis centered below the contamination and the pulse rate produced in the pancake probe was analyzed.