Calculation of radiation dose at a bone-to-marrow interface using Monte Carlo modeling techniques (EGS4)

Radiation dose rate profiles at a bone-to-marrow interface were calculated by simulating a uniform radiation source at the center of the endosteal layer in a long bone. Isotopes (153Sm, 186Re, and 166Ho) were assumed to assimilate as surface agents and the dose profiles were calculated on a microscopic scale using the Electron-Gamma Shower (EGS4) computer program. We validated our computational model against published dose factors (delta) for uniform volume distributed sources replicating them to an accuracy of better than 95%. The calculated dose distributions illustrate the relative contribution of atomic electrons, beta, and photon fractions. The backscatter contribution to marrow dose increased from 3% to 4% at the source to 6% to 8% at a marrow depth of 100 microns. Backscattered dose fraction was not significantly different among the three isotopes. The dose contribution from the three isotopes was remarkably similar at ranges between 25 and 125 microns.

A comparison of results for the University of Missouri Research Reactor radiological airborne release assessments obtained from PC-based computer programs.

The United States Environmental Protection Agency has published three computer programs, COMPLY, AIRDOS-PC, and CAP88-PC, to assist the regulated community in determining compliance with the Environmental Protection Agency radionuclide air emission standards. The programs calculate radiation doses from routine airborne release to the general public residing outside a nuclear facility site. They consider doses from inhalation, ingestion of contaminated food, air immersion, and ground deposition. A PC-based computer code, XOQDOQ-82, developed for the Nuclear Regulatory Commission, was also chosen to compare and evaluate dispersion results from the Environmental Protection Agency codes for the University of Missouri Research Reactor Center. Effects of building parameters, terrain conditions, and downwind distances on dispersion factors were calculated. The results of this study indicated that dispersion factors calculated using AIRDOS-PC and CAP88-PC were several times lower than those calculated using XOQDOQ-82 at all distances, and those dispersion factors calculated using COMPLY were several times lower than the XOQDOQ-82 values at distances greater than 600 m.