Adding Radionuclides to the Varskin 3 Library Correctly
J.S. Durham (Colorado State University)
One of the biggest improvements in the skin dose computer code Varskin 3 is the ability for the user to create a custom radionuclide library. The library contains only the radionuclides chosen by the user and adding a radionuclide to the library takes does not require knowledge of basic nuclear physics. For each radionuclide added to the library, the user must choose the cutoff energy and yield (% emitted per disintegration); decay paths for the chosen radionuclide that fail to exceed both criteria will not be included in the library file for that radionuclide. The same values of cutoff energy and yield are applied to both the beta and gamma component of the dose. For calculations of beta dose, choosing the default cutoff energy of 1 eV and default cutoff yield of 0.1 % will not result in incorrect calculations. However, the cutoff energy is critical when using Varskin 3 to calculate the gamma dose and depend on the skin depth at which the calculation is performed and the thickness of cover material between the source and the skin. This presentation describes the methodologies used to calculate beta and gamma dose in Varskin 3, discusses the implications of the cutoff energy when calculating gamma dose, and provides sample calculations that demonstrate the dependence of gamma dose on the cutoff energy. Guidance in the appropriate choice of the cutoff energy is also provided.
