times and reach the ground some distance downwind. These more distant particles tend to have more cesium (daughter of gaseous xenon) and stroatium (daughter of gaseous krypton) relative to other fission product activities than do the heavier, and thus nearby, particles. Thus, the rather few surface explosions at Iniwetok Atoll tended through fractionation to result in the amounts of cesium-137 and strontium-90 deposited on the test island and nearby islands being less relative to other fission products than the amounts produced by fission in the nuclear explosion. BEST AVAILABLE COPY An example of this fractionation is provided by analyses of the particles in the cloud from the La Crosse test (Nathans, 1970), La Crosse was a coral surface burst of about 40 kilotons on Runit Island. The camnle nf the radioactive cloud was collected at 6500 meters at 2.6 hours after the event. The specific activity (the radioactive with a smaller 9-micron diameter particle. (Little variation was found in specific activities between the smaller particle sizes ranging between 0.5 and 13 microns.) Radionuclide Specific Activity for 9 microns Specific Activity for 50 microns strontium-90 296 promethium-147 229 uranium 0.47 5 “ SOMES ed Tk TI, A aWer’ factors when the largest particle of 50-microns diameter is compared newnanan: * was found to increase with decreasing particle size by the following so eee ire ane rae a disentegrations per unit time and per unit weight of the particle)