Figure 2 shows that the calculated decay for fallout from shot Harry is little different from that presented by Glasstone and Dolan which is “a reasonable average for situations in which the fallout activity arises mostly from fission products." (G177, pp. 392, 393, 450) The best in-situ fallout decay curves were measured in operation Plumbob in 1957 (Di57). lonaest time. The decay of Smoky debris was followed for the This calculation and data from shot Smoky (Di57) agree well within the precision of the measurements, 10% (Fig. 3). The data taken after 100 hr are generally lower than the calculated values. This may be due to the effects of weathering or because radiation levels under 10 mR/hr were measured with an instrument different from that used at levels over 10 mR/hr. | Data for the fallout patterns were normally taken 6-30 hr postshot and brought to a common time, (Sh59) 12 hr postshot, by the decay law ghee, Dunning (Du58) proposed a prescription for the decay of fallout which is t74+2 decay for the first week after a detonation, prt.3 for the second week and prl4 thereafter. Figure 4 shows good agreement between this calculation, the early decay law, and Dunnina's prescription. NUCLIDES ACCOUNTING FOR A MAJOR FRACTION OF EXPOSURE The 5 mass numbers giving the highest external gamma-ray exposure rates were determined for each of 10 decay times from the calculations of fractionated and unfractionated Harry and Smoky debris. products were the same as those found in the calculations of The fission