Global fallout technetium-99 levels in Japanese paddy soils

Determination of global fallout 99Tc in Japanese paddy field soil sample was carried out using a simple and rapid separation method by using a TEVA resin and determination by lCP-MS. The ranges of 99Tc concentrations are 6-110 mBq kg-1 dry. The 99Tc values obtained were usually higher than the expected value of 6 mBq kg-1 dry which was estimated from uniform 99Tc distribution on the surface of the northern hemisphere. To explain the fate of 99Tc in the paddy field environment, 137Cs was used as an indicator. The activity ratios of 99Tc/137Cs are (2.0 - 5.2) x 10-3. Since the activity ratio can be calculated theoretically from fission as 1.4 x 10-4 at nuclear weapons, detonations, the ratio is now estimated to be about 3.0 x 10-4 with correction of decay out. The measured ratios were one order of magnitude higher than the theoretical one from fission. The results of this study, at least, suggest that more Tc might be fixed on the soil than we expected before. (author)