* . » i286 asin Ri iil TABLE 6,1 ~ Fallout and Evacuation Tines Island 6.2 Estimated Initial Fallout Tines (hours) Evacuation Time (hours) . Rongerik H+ 6,8 H + 28.5 (8 men) Rongelap H+h H + 50 (16 people) Ailinginae H+ H+ 38 Utirik H + 22 H+ 55 to H + 78 H + 3k (20 men) H + Sl (48 people) ESTIMATES OF FALLOUT DURATION The rate of increase of radiation intensity, the time at which it reached its maximum level due to decrease of fallout, and the total duration of the fallout can only be estimated on circumstantial grounds, The data of Table 2,1 for Rongerik are not sufficient to warrant an ex- trapolation over two orders of magnitude, It is unlikely that the increase of intensity was sinply linear either on Hongerik or any of the other islands, But, if the rate of increase is assumed constant and extrapolated to a point for which subsequent decay alone would re- duce the dose rate to the values found at later times, a fallout tine of 16 hours on Rongerik, for example, is found to be a necessary conse- quence (Curve a, Figure 6.1). That is to say, 16 hours would have elapsed at such a constant fallout dose rate increass before the time of maximum dose rate on the island would have occurred = the time at which the fallout was increasing the radioactivity level at the sane rate that radioactive decay was reducing it. For such a constant build up, this equality would have occurred only for an instant, (Point 4)), after which the fallout would have suddenly ceased, The actual fallout must, of course, have had a variable rate of increase and decrease, reaching a maximum and gradually decreasing to the rate governed by decay alone. However, using the initial rate of increase and drawing a more gradual maximum would place the cessation of the fallout at an even later time (Curve b, Point Aj). Since the visible fallout is believed to have ceased sometime after midnight on 2 March or at about H +18 hours (Point 43); an increase in the rate of increase after a short time was almost certainly the case (Curves c, d, ande), But the steepness of this rate of increase, the sharp ness of the maximum point and the gradualness of the fallout dimimtion are unknown, so that there is no direct evidence to show whether Curve c or Curve e, for instance, is closer to representing the event, There are, however, indirect indications, Monitor data from previous nuclear events have indicated that a radioactive cloud is not ; |