ial | These data were reported by Eisenbud and Harley (8) covering fallout through June 1957. The model was applied only to the results obtained after ‘ ery May 1956, Unfortunately, later calculations have cast doubt on the validity of the effective burst date concept and actual errors of computation have been The present model was designed to overcome some of the objections to the previous one. All of the data since the beginning of 1954 have been recomputed according to this third model, 4 rose uneovered, It would have been technically possible to introduce a number of experimentally determined refinements into the model, but the cost of compu- tation for some 375,000 pieces of data would have been prohibitive, There- fore, the relatively simple model described had to be accepted. The_ utation Model The present model was designed to take into account new data on sr70 yield, stratospheric and tropospheric residence times and the decay of Sr, The model will first be outlined and then its defects will be discussed, 1. An estimate of the fission yield is obtained for each weapon test. 2. The value of 133 megacuries of beta activity per nominal bomb?) The value of 0.00105 percent of sr? is used to obtain total megacuries of Sr90 at one day. 4. The megacuries of mixed fission products produced in each test are decayed by the q-l.2 law for each subsequent day and the results for all tests summed. 5. The megacuries of Sr90 produced in each test are decayed with a half-life of 27.7 years for each subsequent day and the results for all tests summed, 6. Both the mixed fission products and Sr?0 are also corrected for tropospheric ( < 3/4 MI) and stratospheric (> 3/4 MT) deposition using half-residence times of 20 days and 4 years respectively. Fs ~5- k 3 3. is used to obtain total megacuries of fission products at one day.