VARSKIN 4: A Computer Code for Skin Contamination Dosimetry (NUREG/CR-6918, Revision 1)
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Manuscript Completed: April 2011
Date Published: June 2011
D.M. Hamby, C.J. Lodwick, T.S. Palmer, S.R. Reese, and K.A. Higley
Department of Nuclear Engineering and Radiation Health Physics
Oregon State University
Corvallis, OR 97331-5902
M. Saba, NRC Project Manager
Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Office of Nuclear Regulatory Research
The original VARSKIN computer code, an algorithm to calculate skin dose from radioactive skin contamination, has been modified on several occasions. Last version of this code, VARSKIN 3, enables users to calculate the skin dose (from both beta and gamma sources) attributable to radioactive contamination of skin or protective clothing. The code also offers the ability to compute the dose at any skin depth or skin volume, with point, disk, cylindrical, spherical, or slab (rectangular) sources, and even enables users to compute doses from multiple sources. The input data file was also modified for VARSKIN 3 to reflect current physical data, include the dose contribution from internal conversion and Auger electrons, and allow a correction for low-energy electrons.
The VARSKIN 4 code is designed to operate in both Windows® and Maclntosh® environments and is expected to be significantly easier to learn and use than its predecessors. PC and MAC users will download different executable files, but the functionality is identical. Five different predefined source configurations are available in VARSKIN 4 to allow simulations of point, disk, cylinder, sphere, and slab sources. Improvements to VARSKIN 4 include an enhanced photon dosimetry model, as well as models to account for air gap and cover materials for photon dosimetry. Although the user can choose any dose-averaging area, the default area for skin dose calculations in VARSKIN 4 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, and the user does not need to enter the data in any particular order. 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 photons, internal conversion electrons, and Auger electrons. VARSKIN 4 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 to provide guidance and to offer new users a tutorial in the use of VARSKIN.
VARSKIN 4 introduces an upgraded photon dosimetry model without changing any previous modeling schemes for beta dosimetry. The enhanced photon model 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 syringe model (available in previous versions of VARSKIN) has been removed from use in VARSKIN 4 because it was not sufficiently detailed to yield accurate dose results and most of users of the code did not find it useful.
This document describes the VARSKIN 4 code, which is used by the NRC staff to perform confirmatory calculations of licensees' submittals regarding skin dose estimates. This report provides basic operating instructions, presents detailed descriptions of dosimetry models, and suggests methods for avoiding misuse of the code.