Alpha contamination of the skin: dose and LET distribution at depths corresponding to the epidermal thickness of skin

Recently it has been reported that the thickness of the epidermal layer of skin can be as low as 2–4 mg/cm2 in certain parts of the body (HARVEY, 1971; WHITTON, 1971; WHITTON, 1973). In these areas, alpha contamination could result in the irradiation of basal layer cells. In order to evaluate the associated hazard, the energy distribution and dose of alpha particles from 210Po and 242Cm have been measured at various depths. By computing the LET distribution, the Quality Factor (QF) for alpha irradiation of basal cells has been calculated to be 20. If an average epidermal thickness of 4 mg/cm2 is accepted for radiation protection purposes (WHITTON, 1973), contamination by alpha particles of energy 5.7 MeV and above can result in the irradiation of basal layer cells. For the current permissible skin contamination value of 10−5microCi/cm2, the dose rate at this depth from 242Cm (6.11 MeV) is about 45 mrem/hr. Thus the dose to the skin becomes the limiting factor for arriving at the permissible skin contamination. Hence, it is desirable to lower the contamination level for energetic alpha particles.