Monte Carlo simulation of enriched uranium in the lungs of thorax voxel phantom for assessment of enrichment and its effect on dose

Highlights: • Simulation of photon energies of ²³⁸U, ²³⁴U, ²³⁵U & daughter products for uniform source distribution in the lungs. • Evaluation of probabilities of photon energies per unit disintegration of natural and enriched uranium compositions. • Generation of lung spectra of HPGe array for various enrichments of uranium using Monte Carlo simulations. • Evaluation of unknown enrichment in the range of 2 % to 30 % from lung spectrum analysis. • Evaluation of minimum detectable dose from lung measurements due to enriched uranium intake. In-vivo lung monitoring is an important technique for the assessment of internal dose of radiation workers handling actinides. At BARC, counting efficiencies (CEs) of detection systems used for estimation of natural uranium in the lungs are evaluated using realistic thorax physical phantoms or computational voxel phantoms. The quantification of ²³⁸U and ²³⁵U in lungs is done using CEs determined at 63.3 keV and 185.7 keV photon energies respectively. These CEs can also be used for assessment of enriched uranium in the lungs of the workers. In this study, spectra are generated for HPGe array detectors using Monte Carlo simulations of various enriched uranium compositions distributed in the lungs of thorax voxel phantom. A methodology is developed to predict the ²³⁵U enrichment from lung spectrum analysis using the ratio of net counts in 185.7 keV and 63.3 keV energy regions. It is possible to estimate enrichments in the range of 2%–30% using the developed method with less than ±9% error. Finally, effect of ²³⁵U enrichment on dose assessment using lung monitoring method is studied.