same as that from the seventh hour until one week later. Further, this first-week dose would be about twice as great as the entire re~ maining dose possible for the lifetime of the activity. (Figure 3). This rapid decay suggests the benefits of protection in the early : periods after fallout and, where possible, delay of entry into a contaminated area. In localities downwind where initial fallout night not occur until say, 24 hours after a detonation, the situation would be somewhat different, in that the radioactive decay would be slower. For example, consider the cases where fallout occurred at (a) one hour, and (b) 24 hours, after a detonation. One day after fallout the dose rate in the first case would be 1/45 of its initial activity (lst hour), but in the second case the dose rate would have decreased to only slightly less than 1/2 of its initial activity (24th hour). The above estimates are based on an assumed radiological decay of (time)~1-2. This is reasonably accurate for early periods of time after detonation, but the decay may start to vary significantly from the theoretical curve after several months have elapsed. (Figure 4). At times later than shown in Figure 4 the decay curve would be expected to flatten out due to the presence of long lived cesium-137. 2. (Twenty-seven year half-life) Weatheringand shieldingeffects. The magnitude and time of occurrence of weathering and shielding makes it impossible to establish a single establishment of a precise rule of effects covering all situations, impossible, yet these meee | f -