The fall-out was solid particulate made up of calcium hydroxide with a very thin layer of calcium carbonate on the outer surface. The fission products were trapped within the particulate. Those particles that arrived in such an environment as sea-washed decking were slowly dissolved, with a resulting reprecipitation of the calcium ion by the sulfate ion which exists in comparatively high concentration in sea water. Asa result of this phenomenon, many hollow particles formed and firmly adhered to all surfaces they touched. The fission products readily leached from the particulate exposed to rain water. The leached activity was both ionic species and colloids. The quantity of primary fall-out in the cross-wind direction varied from some value over 20 g/sq ft at 4 miles to 0 g/sq ft at 15 miles. The particle diameters of the radioactive fall-out varied from less than 10 » to greater than 5000 pu. There was no particle-size fractionation with cross-wind distance and only meager evidence of any with time. The cross-~wind fall-out arrival time was entirely independent of distance from ground zero; duration of fall-out was approximately 1 to 2 hr. There was a random distribution of activity with time at all stations in the cross-wind radiation field. 7.1.2 Secondary Fall-out Secondary fall-out arrived over an extensive area of the Pacific around Eniwetok Atoll. The period of secondary fall-out was several days at any one location, arriving from 2 to 5 days after the detonation, None of the secondaryfall-out was of military significance since a gamma doserate of less than 10 mr/hr wasnotedatall collecting stations. In no case was any of the secondary fall-out particulate over 25 u in diameter. The secondary fall-out arrived from an initial height greater than 80,000 ft. 7.2 RECOMMENDATIONS Experience gained during the work on this project makes possible certain suggestions for consideration in the planning of future operations. The inability to predict the area of primary fall-out well in advance of shot time can be presumedto be definitely established. Conse- quently it is recommended that a 360° coverage of collecting stations be provided in future tests, Furthermore the use of free-floating stations can be considered practical and highly desirable if a method for their positive location is provided, Whatever methods that are devised for locating the free-floating stations must not interfere with the task force security search patrol. Therefore it is recommended that a lightweight coded signaling device such as the British Ultra Air Sea Rescue beacon be installed on each of the free-floating stations. - 55-56