United States Nuclear Regulatory Commission - Protecting People and the Environment

VARSKIN 6: A Computer Code for Skin Contamination Dosimetry (NUREG/CR-6918, Revision 3)

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Publication Information

Manuscript Completed: December 2017
Date Published: October 2018

Prepared by:
D. M. Hamby
C. D. Mangini

School of Nuclear Science and Engineering
Oregon State University
Corvallis, OR 97331-5902

V.Shaffer, NRC Project Manager

Office of Nuclear Regulatory Research

Availability Notice

Abstract

The original VARSKIN computer code, an algorithm to calculate skin dose from radioactive skin contamination, has been modified on several occasions. VARSKIN is a U.S. NRC computer code used by staff members and NRC licensees to calculate occupational dose to the skin resulting from exposure to radiation emitted from hot particles or other contamination on or near the skin. These assessments are required by 10 CFR 20.1201(c) in which the assigned shallow dose equivalent is to the part of the body receiving the highest exposure over a contiguous 10 cm2 of skin at a tissue depth of 0.007 centimeters (7 mg/cm2).

As with previous versions, five different predefined source configurations are available in VARSKIN to allow simulations of point, disk, cylinder, sphere, and slab sources. Improvements to the earlier VARSKIN versions included enhanced photon and electron dosimetry models, as well as models to account for air gap and cover materials for photon dosimetry. With a simple check box activated by the user, VARSKIN 6 gives the user the option to have the code automatically include all decay products in dosimetry calculations or to allow the user to manually add progeny. Additionally, the option to calculate skin dose using ICRP 107 nuclide decay data (ICRP 2008) has been added. Both ICPR 38 (1983) and ICRP 107 (2008) nuclide libraries are available at the user's option and contain data on gamma rays, X rays, beta particles, internal conversion electrons, and Auger electrons. Although the user can choose any dose-averaging area, the default area for skin dose calculations is 10 square centimeters, to conform to regulatory requirements pursuant to Title 10 of the Code of Federal Regulations, Section 20.1201(c). Data entry is condensed to a single screen, a variety of unit options are provided (including both British and International System (SI) units), and the source strength can be entered in units of total activity or distributed in units of activity per unit area or activity per unit volume. The output page and the user's ability to add radionuclides to the library are greatly simplified. VARSKIN allows the user to eliminate radionuclides that are not of interest and thus build a customized library.

The enhanced photon model, introduced in VARSKIN 4, accounts for photon attenuation, charged particle buildup, and electron scatter at all depths in skin. The model allows for volumetric sources and clothing/air gaps between source and skin. The electron dosimetry model was upgraded in VARSKIN 5 to better account for beta energy loss and particle scatter. Dose point kernels are now Monte-Carlo based and results agree very well with EGS and MCNP probabilistic simulations.

This document describes the VARSKIN 6 dosimetry code, provides basic operating instructions, presents detailed descriptions of dosimetry models, and suggests methods for avoiding misuse of those models.

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Page Last Reviewed/Updated Monday, October 22, 2018