Accounting of 131l decomposition under retrospective assessment of its deposition on the basis of determination of 129l deposition

Abstract

It is known that after the Chernobyl accident on the territories with deposition density of 137Cs less than 3.7x10" Bq/kg insufficient number of direct thyroid measurements for the public and a limited number of the spectrometrical measurements of 131l in soil were conducted. At the same time, in the case of availability of representative number of the estimates of the 131l ground deposition density for the territory under consideration, reliable estimates of the average dose to the thyroid for the public in a given settlement can be derived, for example for an adult population with further assessment of the doses for the residents of the other age-groups. In this regard, reconstruction of the ground deposition density of 131l (during the significant period of thyroid dose formation) on the basis of the determination of the ground deposition density of 129l is very helpful for reconstruction of the estimates of the thyroid dose for the residents of the settlements, for which the estimates of the 137Cs deposition density are available. However, to find a solution was necessary to resolve a specific but important task that distinguished from 129l (half-life is equal to 1.6x107 years) the level of 131l (half-life is equal to 8.04 days) was substantially decreasing during the period of thyroid dose formation. The given article aimed a justification of approaches to account of radioactive decay of 131l in the course of determination of its ground deposition density on the basis of determination of the ground deposition density of 129l at the late stage after the accident.

Keywords

• dose
• ground deposition density of radioiodine
• iodine migration