Determination of 99Tc deposited on the ground within the 30-km zone around the Chernobyl reactor and estimation of 99Tc released into atmosphere by the accident.

Technetium-99 was determined in samples from the 30-km zone around the Chernobyl reactor. Concentrations of 99Tc in soil samples taken from three forest sites ranged from 1.1 to 14.1 Bq kg-1 dry weight for the organic soil layers, and from 0.13 to 0.83 Bq kg-1 dry weight for the mineral soil layers. In particular, for the organic layers, the measured 99Tc concentrations were one or two orders of magnitude higher than those due to global fallout 99Tc. The 99Tc depositions (Bq m-2), based on the sum of the depositions measured in organic and mineral layers, ranged from 130 Bq m-2 within the 10-km zone to about 20 Bq m-2 close to the border of the 30-km zone. Taking the corresponding measured 137Cs depositions into account, it was found that the activity ratio of 99Tc/137Cs ranged from 6 x 10(-5) to 1.2 x 10(-4). It was estimated that about 970 GBq of 99Tc had been released by the Chernobyl accident. This figure corresponded to 2%-3% of the total 99Tc inventory in the core.