cent and 50 percent of the cloud radius, respectively, and applying methods based on accepted meteorological procedures. Modified particle fail-rate equations were used and corrections were made for time and spatial variation of the winds. With the same assumptions, rough agree. ment was also achieved for Shots Flathead and Navajo by neglecting spatial variation of the Winds, in spite of the gross differences in the character of the fallout. The reason for this agreementjg not well understood. Predicted fallout arrival times were often shorter by 10 to 25 percent than _ the measured times, and the maximum particle sizes predicted at the times of arrival, peak, and cessation were usually smaller by 10 to 50 percent than the measured sizes. 3. The weighted mean values of the activity collected per unit area on the standard platform constitute a set of relative measurements, varying as a function of wind velocity and particle terminal velocity. The exact form of this function is not known; it appears, however, that the airflow characteristics of the platform were sufficiently uniform over the range of wind velocities encountered to make particle terminal velocity the controlling factor. The activity-perunit-area measurements made on the samples from the skiffs may constitute a second set of relative values, and those made on samples from the raft and island minor arrays, a third set, closely related to the second. 4. The maximum platform collections should be utilized as the best estimate of the total amount of activity deposited per unit area. An error of about +50 percent should be associated with each value, however, to allow for measurement error, collection bias, and other uncertainties. Although this procedure is Strictly applicable only in those cases where single-wind deposition prevailed, comparable accuracy may be achieved by doubling the mean platform value and retaining the same percent error. 5. Decay of unfractionated fission products according tot m1.2 is adequate for planning and estimating purposes. Wheneverfractionation exists or significant induced activities are present, however, an actual decay curve measured in a counter with known response characteristics, or computed for the specific radionuclide composition involved, should be used. Errors of 50 percent or more can easily result from misapplication of the t™':? rule in computations involving radiological effects. 6. It is possible to determine fraction of device by iron or residual uranium with an accuracy comparable to a Mo”? determination, but the requirements for a large sample, low background, and detailed device information are severe. In general, fractions calculated from these elements tended to be high. were not reported. Analysis of copper, aluminum, and lead produced very high results which It is probable that backgrounds from all sources were principally responsi- ble, because the amounts of these elements expected from the Redwing devices were quite small. 7. The time-intensity recorders consistently measured less gamma ionization dose than film dosimeters located on the same platforms. In those cases where the geometry remained nearly constant and comparisons could be made, this deficiency totaled ~ 30 to 60 percent, in qualitative agreement with the response characteristics of the instrument estimated by other methods. 8. Because nearly equal amounts of fallout per unit area were collected over approximately the same time interval by the incremental collector, high volumefilter, and open-close collectors on the ship platforms, it appears that air filtration through a medium exposed to direct faliout at face velocities up to 1.7 mph offers no substantial advantage over passive fallout sampling. It is apparent that under such conditions the collections are not proportional to the volume of air filtered, and should not be interpreted as implying the existence of an independent aerosol hazard. 9. The contamination index, which provides a measure of the relative fallout ionization rate for unit device yield per unit area, is approximately proportional to the ratio of fission yield to total yield of the device. 5.2 RECOMMENDATIONS It is believed that the preceding results emphasize the desirability of making the following additional measurements and analyses. 1. Time of fallout arrival, rate of arrival, time of peak, and time of cessation should be 154