EFFECTIVE HALF-LIVES OF I-ISOTOPES AND CS-ISOTOPES IN GRASSLAND SHORTLY AFTER FALLOUT

The effective half-lives of I- and Cs-isotopes in grass immediately af ter radioactive fallout were determined in agricultural grassland at s everal sites in Austria after the Chernobyl accident. The effective ha lf-lives observed during the first 83 days after fallout (period of 1 May to 23 July) were 4.6 d for I-131 and 10.5 d for Cs-137 correspondi ng to biological half-lives of 10.7 +/- 3.2 and 10.5 +/- 1.4 d, respec tively. From the effective half-life obtained for grass, the trend of activity concentration in milk expected by feeding this grass is calcu lated and compared to that actually observed in milk after the Chernob yl accident.