Contributions of short-lived radioiodines to thyroid doses received by evacuees from the Chernobyl area estimated using early in vivo activity measurements

A series of in vivo gamma spectrometric measurements of 65 people evacuated from Pripyat 1.5 days after the Chernobyl Nuclear Power Plant Unit 4 explosion was performed in St Petersburg, Russia, its early as 30 April 1986. The historical spectra and interviews were recently processed and the results used for thyroid dose estimation. Activities of I-131 in thyroid and Te-132 in lungs were determined easily; for estimation of I-132 and I-133 activities in thyroid. sophisticated methods of spectral processing were developed. According to thyroid measurement data, the mean ratio of I-133/I-131 activities (at the time of the accident) inhaled by residents of Pripyat was 2.0. The mean ratio of thyroid dose from I-133 inhalation to that caused by I-131 amounts to 0.3, which confirms the accuracy of dose estimates based on the evolution of the Chernobyl accident. The mean ratio of I-132 activity in thyroid to that of Te-132 in lungs was assessed from the human measurement data to be 0.2, which is in reasonable agreement with the metabolic properties of these radionuclides. The mean ratio of thyroid dose from I-132 originating from Te-132 deposited in lungs to the dose caused by I-131 was 0.13 +/- 0.02 for Pripyat residents who did not take KI pills and 0.9 +/- 0.1 for persons who took KI pills. Thus, the contribution of short-lived radioiodines to total thyroid dose of Pripyat residents, which was on average 30% for persons who did not use stable iodine prophylaxis, and about 50% for persons who took KI pills on 26-27 April, should be accounted for in the assessment of thyroid health effects.