* meas ble an el ate ee Ah piliRTRe oy TAPLE 6,1 - Fallout and Evacuation Tines Island Estinated Initial iL 6,2 Evacuation Time Fallout Tires (hours) _ (hours) Rongerik H + 6,8 H+ 23.5 (6 men) H+ 34 (20 men) Rongelap 4+h H + SO (15 people) ALlinginae H+ H+ 58 Utirik H + 22 H+ 51 (43 people) ' H+ 55 to H+ B ESTIMATES OF FALLOUT DUATICN The rate of increase of radiation intensity, the time at which 18. reached its maximum level cua to decrease of fallout, and the total 7; duration of the fallout can cnly be estimated on circumstantial grounds, The data of Table 2.1 for Hongerik are not sufficient to warrant an extrapolation over two orders of majnitude, It is unlikely that the increase of intensity was sinply linear either on Kongerik or any of the other islands, FPut, if the rate of increase is assumed constant and extrapolated to a point for which subsequent decay alone would reduce the dose rate to the values found at later tines, a fullout time of 16 hours on Hongerik, for exanple, is found to be a necessary consequence (Curve a, Figure 6.1). That is to say, 16 hours would have elapsed at such a constant fallout dose rate increase before the time of maximum dose rate on the island would have uccurred =- 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 A)), after which the fallout would have suddenly ceased, The actial fallout must, of course, have had a variable rate of increase and decrease, reaching a maximum and cradually decreasing to the rate governed by decay alene, However, using the initial rats of increase and crawing a more gradual maximun would place the cessation of the fallout at an even later time (Curve b, Point Ag). . Since the visible fallout is telieved to have ceased some tine after midnight on 1 March or at about H + 16 hours (Point Aj), an increase in the rate of increase after a short time was almost certainly the case (Curves c, d, and e), But the steepness of this rate of increase, the sharp nesa cf the maximum point and the gradualnass of the fallout dimimtion are unknown, so that. there is no direct evidence to show whether Curve c or Curw a, for instance, is closer to representing the event. There are, however, indirect indications. Moniter data fram pre= vious muclear events have indicated that a radioactive cloud is not xn . . ° Ena