Retrospective evaluation of 131I deposition density and thyroid dose in Poland after the Chernobyl accident.

The 131I deposition in Poland after the Chernobyl accident on 26 April 1986 was evaluated from the determined 129I deposition and the estimated 129I/131I ratio at the time of the arrival of fallout. Concentrations of 129I and 127I were determined by neutron activation analysis in uncultivated soils from 16 locations in Poland. Determination of 137Cs in soils was carried out by gamma spectrometry. The atomic ratio of 129I/131I at the time of fallout arrival was estimated using the 129I/131I ratio at the time of the accident, which, on the basis of the core inventory data, was assumed to be 22.8. It was estimated from the time of fallout arrival and from the weighed mean atomic ratio that the 129I/131I ratio for Poland was 32.8. The calculated 131I deposition ranged from 63.2 to 729 kBq m(-2). High deposition of 131I occurred in the locations with rainfall but occasionally also in locations without rainfall. Committed equivalent doses from 131I were evaluated for 5-y-old children, 10-y-old children, and adults using the computer model CLRP for the situations with and without countermeasures including iodine prophylaxis. The highest thyroid doses from inhalation and ingestion without countermeasures were 178 mSv, 120 mSv, and 45 mSv for 5-y-old children, 10-y-old children, and adults, respectively. The countermeasures reduced these doses by about 30%.