Purpose: This work aims first to improve the reliability of absorbed dose calculation in critical organs of cattle during internal irradiation immediately after radiation accidents by a) improving the compartmental model of radionuclide metabolism in animal body; b) the use of precision computing technologies for modeling as the domain, and the actual radiation transport. In addition, the aim of the work is to determine the agreed values of the 131I critical dose in the cattle thyroid, leading to serious gland dysfunction and its follow-up destruction.
Material and methods: To achieve aforecited goals, comprehensive studies were carried out to specify the parameters of the compartmental model, based on reliable experimental and theoretical data. Voxel technologies were applied for modeling the subject domain (thyroid gland and its environment). Finally, to solve the 131I radiation transport equation, the Monte Carlo code was applied, which takes into account the contribution of gamma and beta radiation source, and the contribution of the entire chain of secondary radiations in the dose calculation, up to the total energy dissipation.
Results: As the main theoretical result, it is necessary to emphasize the conversion factor from the 131I activity, distributed uniformly in volume of the thyroid gland, to the average dose rate in the gland (Bq × Gy/s). This factor was calculated for both cows and calves in the selected domain configuration and thyroid morphology. The main practical result is a reliable estimation the lower bound of the absorbed dose in the thyroid, which in a short time leads to its destruction under internal 131I irradiation: ~300 Gy.
Conclusion: Usage a compartmental model of the 131I metabolism with biokinetic parameters, received on the basis of reliable experimental data, and precise models of both the subject area and radiation transport for evaluation the dose in the cattle thyroid after the radiation accident allowed to obtain reliable values of the thyroid dose, adducting to its destruction at short notice.
Assessment of MCNPX Monte Carlo Code for Absorbed Dose Calculations in Mammogarphy Examination