ENVIRONMENTAL HALF-LIFE OF 137CS Current dose estimates are based only on radiological decay (T1/2=3001Y for 137CS). Environmental processes do eliminate 137CS from the ecosystem Effective half-life AE = xradiological As an example, + to the groundwater. xenvironmental. if ‘E is about 30y, the estimated doses would be half of the currently estimated doses. Thus, TEis a very important parameter to kn~w. No historical data to evaluate XE (or TE). TE is a time dependent process; thus, evaluating TE takes time. Current experiments 1.) Six trees on Enewetak Atoll first sampled in 1973. since then. 2.) Approximately Last sampled in February 1986. 30 trees on Bikini Atoll first sampled in 1978-1979. Sampled at least annually 3.) Sampled periodically since then. About eight sites first sampled in 1959 by the University of Washington have been resampled in February of this year. years, respectively. 2’ Thus, we could gain 27