VARSKIN 5: A Computer Code for Skin Contamination Dosimetry (NUREG/CR-6918, Revision 2)

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Publication Information

Manuscript Completed: October 2013
Date Published: July 2014

Prepared by:
D. M. Hamby, C. D. Mangini, J. A. Caffrey, M. Tang

Department of Nuclear Engineering and Radiation Health Physics
Oregon State University
Corvallis, OR 97331-5902

M. Saba, NRC Project Manager
S. Sherbini, NRC Technical Monitor

Office of Nuclear Regulatory Research

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The original VARSKIN computer code, an algorithm to calculate skin dose from radioactive skin contamination, has been modified on several occasions. This program is a rewrite of the U.S. NRC computer program VARSKIN 4 which is 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 VARSKIN 4, five different predefined source configurations are available in VARSKIN 5 to allow simulations of point, disk, cylinder, sphere, and slab sources. Improvements to the earlier VARSKIN 3 and 4 included an enhanced photon dosimetry model, as well as models to account for air gap and cover materials for photon dosimetry. The new VARSKIN 5 version has been updated to better predict beta dosimetry in shallow skin targets. Although the user can choose any dose-averaging area, the default area for skin dose calculations in VARSKIN 5 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. A library file contains data on gamma rays, x-rays, beta particles, internal conversion electrons, and Auger electrons. VARSKIN 5 allows the user to eliminate radionuclides that are not of interest and thus build a customized library. Finally, an extensive, context-sensitive help file is made available for VARSKIN 5 to provide guidance and to offer new users a tutorial in the use of the skin dosimetry software.

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 beta dosimetry model has been upgraded in VARSKIN 5 to better account for beta energy loss and particle scatter. Dose point kernels are now Monte Carlo based and the code agrees very well with the EGSnrc Monte Carlo code.

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

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