Answer to Question #8268 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
How were 0.07 mm (70 µm) and 10 mm determined as the distances below the skin for extremity and effective whole-body dose respectively?
The thickness of the epidermis in adults varies from about 5-10 mg cm2 (50-100 m) on the head, trunk, arms, and legs, and may approach 40 mg cm2 (400 m) on the palms of the hands and soles of the feet (ICRP 2003). A "reference" value of 70 m has been used for many years as a representative average and was reiterated in the most recent International Commission on Radiological Protection (ICRP) recommendations for anatomical reference standards (ICRP 2003). This is also codified in the principal regulations regarding the protection of radiation workers (10 CFR 20) (U.S. NRC). For calculations of the "deep dose," a depth was chosen to represent the maximum dose at some point beneath the surface of the body where dose is expected to reach a maximum, based on considerations of charged particle equilibrium. This varies considerably for different radiations and different energies of the radiations, but this value of 10 mm has been used as a reasonable value for many years (ICRP 2008) and is similarly codified in 10 CFR 20 (U.S. NRC).
Michael G. Stabin, PhD, CHP
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