uniformly high in activity throughout, the first portion being the most intense and the balance tailing off, Initially heavy fallout has been reported to produce a peak of airborne radioactivity soon after its arrival, with the airborne activity level then decreasing. The latter part of a fallout, though still observable as dust, may then add only a small’ fraction to the total dose due both to aerosol and material already on the ground, especially if radioactivity was mainly confined to the larger particles which fell out most quickly, If this is the case, the total phenomenon would tend toward the effect of a shorter fallout, and the total dose would then be best estimated by assuming the fallout to have been complete in some shorter "effective" time, such as Curve f, - The Rongerik film badge data in Table 2.3 may be used to derive such an effective fallout time estimate. This procedure was followed, The decay rate, energy spectrum, and meter response discussed in Chap= -ters 3 and 5 were used and the later dase rate measurement on Rongerik (Table 2,4) was taken as a starting point, The upper limit of dose found with the outdoor tadge readings (approximately 1C0 r Table 6.1) then resulted from assuming a 12-hour "effective constant fallout" time. This was, therefore, taken as a most protable tine and the resulting straight line midway between Curves a and f in Figure 6,1 was used in calculating the probable 12-hour cose for each island (Curve g)- Though this estimate differs appreciably from that of 1 hour shetansth heitcldandattnsants which was originally used as an effective time in Reference 16, the later spectrum, decay rate, and meter response estimates made a l2-hour value more plausible if the film badge readings were accepted, Keeping a lehcur assumption wculd have resulted in a dose some 50 percent higher than the outdoor badge readings showed, Since the accuracy of the film badge readings was believed to be better than 50 percent, the l2-hcur value was therefore used, as it is more consistent with all the other available information, Nevertheless, the duration of fallout still remains the least known parameter of the exposures, 32 oo ae #0 © ee ese & as te a ge o« e e © ee Paeer see -_ oe 2a 6