Evaluation of doses of beta-irradiation of the thyroid gland of cows according to the gama-background in the area of its location

When I-131 enters the body, it accumulates in the thyroid gland of animals, leading to degeneration of its parenchyma. The degree of damage depends on the dose of beta-radiation. The beta-radiation dose can be estimated based on the activity of incorporated I-131 using either appropriate mathematical models or the formula by Marks et al. The experience of eliminating the consequences of the Chernobyl nuclear power plant accident has shown that veterinary specialists in the initial period could only measure the radiation background on the ground and in the thyroid gland of animals. The aim of this study was to estimate the dose of beta-radiation to the thyroid gland of cows from I-131 based on the level of gama-radiation in the thyroid region. The activity of I-131 was calculated from the intensity of gama-radiation in the thyroid gland area. Based on the dependence between the beta-radiation dose to the thyroid gland of cows and the gama-radiation intensity in its region, calculated using the model and formula, an average proportionality coefficient (K=0.4) was determined. At beta-radiation doses to the thyroid gland of up to 30 Gy, animals can be used without restrictions. At doses of 100 Gy or higher, animals must be slaughtered within 45-60 days after veterinary procedures aimed at reducing 131Cs levels in the body. For doses of up to 100 Gy, animals require regular veterinary monitoring. Absorbed beta-radiation doses of 30, 60, and 100 Gy correspond to gama-radiation dose rates of 75, 150, and 250 mR/h in the thyroid region, respectively. The beta-radiation dose significantly depends on the morphometric characteristics of the thyroid gland, which are influenced by the breed, age, productivity of the animals, and the season. Therefore, the calculated beta-radiation doses are approximate, and the calculation method is applicable only to adult animals.