Rääf C L, Tondel M, Isaksson M
Medical Radiation Physics, Department of Translational Medicine (ITM), Lund University, Sweden.
J Radiol Prot. 2019 Apr;39(2):522-547. doi: 10.1088/1361-6498/ab0577. Epub 2019 Feb 8.
The time-integrated absorbed dose to the thyroid gland in the years after a fallout event can indicate the potential excess number of thyroid cancers among young individuals after a radionuclide release. Typical mean values of the absorbed dose to the thyroid have been calculated previously using reported data on radioiodine obtained from air sampling and dairy milk surveys in Sweden after the Chernobyl fallout, not including the contribution from Cs and Cs. We have developed a model for Swedish conditions taking these additional dose contributions into account. Our estimate of the average time-integrated absorbed dose to the thyroid, D , during the first 5 years after fallout ranged from 0.5-4.1 mGy for infants and from 0.3-3.3 mGy for adults. The contribution to D from I through inhalation and milk consumption varied considerably among different regions of Sweden, ranging from 9%-79% in infants, and from 4%-58% in adults. The external irradiation and exposure from the ingestion of Cs in foodstuffs accounted for the remaining contributions to D (i.e. up to 96% for adults). These large variations can be explained by the highly diverse conditions in the regions studied, such as different degrees of fractionation between wet and dry deposition, different grazing restrictions on dairy cattle, and differences in Cs transfers through food resulting from differences in the local fallout. It is our conclusion that the main contribution to D from nuclear power plant fallout in areas subjected to predominantly wet deposition will be from external exposure from ground deposition, followed by internal exposure from contaminated food containing the long-lived fission product Cs and the neutron-activated fission product Cs. The contribution from Cs to the thyroid absorbed dose should thus be taken into account in future epidemiological studies.
沉降事件发生后的数年中，甲状腺的时间积分吸收剂量可表明放射性核素释放后年轻人中可能额外出现的甲状腺癌病例数。此前曾利用瑞典在切尔诺贝利沉降事件后通过空气采样和牛奶调查获得的放射性碘报告数据计算甲状腺吸收剂量的典型均值，其中未包括铯和铯的贡献。我们针对瑞典的情况开发了一个模型，将这些额外的剂量贡献考虑在内。我们对沉降事件后前5年甲状腺平均时间积分吸收剂量D的估计值为：婴儿为0.5 - 4.1毫戈瑞，成人为0.3 - 3.3毫戈瑞。通过吸入和饮用牛奶摄入碘对D的贡献在瑞典不同地区差异很大，婴儿中为9% - 79%，成人中为4% - 58%。食品中铯的外照射和摄入造成的暴露占D的其余贡献（即成人中高达96%）。这些巨大差异可由所研究地区高度多样的条件来解释，例如湿沉降和干沉降之间不同程度的分馏、对奶牛不同的放牧限制以及当地沉降差异导致的铯在食物中的转移差异。我们的结论是，在主要为湿沉降的地区，核电站沉降对D的主要贡献将来自地面沉降的外照射，其次是含有长寿命裂变产物铯和中子活化裂变产物铯的受污染食物的内照射。因此，在未来的流行病学研究中应考虑铯对甲状腺吸收剂量的贡献。
