approximate number median diameters of samples collected ranged from 5e2 to 20 me Up to forty~three per cent of these particles were under 10 pp in diameter. Shot 1 particles appeared to be coral or crystalline; those from Shot 3 appeared to be mostly crystalline, ashlike, or fused. In particles from 149 to 1000 p, the percentage of particles with activity on the outside generally increased directly with size, while the percentage of uniformly radioactive particles generelly decreased with size. These two types of particles accounted for about 90 per cent of the radioactive particles examined. Activity was scattered randomly throughout the remining 10 per cent of particles. There was no apparent correlation between the location of activ- ity on the particles and tneir physical appearance. No conclusions could be drawn about the presence or absence of radioactivity in the base surge, because no samples were obtained in the base surge region. 4.1 RECOMMENDATIONS The properties and effects of fallout from new and untried types of detonations should continue to be studied at future operations. The time and rate of arrival of primary fallout should be determined at the great distances at which fallout oan be a hasard to human life, as well as at close-in locations. When a base surge is predicted as one of the effects of a detonation, attempts szculd agein be made to determine whether radicactivity ie carried in that base surge. The differences in characteristics of fallout between land and water shota should be more thoroughly determined at future tests. Rates of beta and gamma activity should be known with more certainty at early times, and hence, efforts should be made to cbserve and study decay at early times after the detonation. The characteristics of fallout particles, particularly from water shots, should be investigated at future tests. The presence or absence of an internal radiological respiratory hazard should be established when new type detonation conditions become available. Systematic recording of gamma radiation levels should continue to be made at varying distances from ground Zero. Ground level activities around ground zero should be determined by employing heliccpter aerial survey system or other means, 4.2 RECOMMENDATIONS When devices to be detonated have & yield of the order of mag- nitude of the larger CASTLE shots, documentation of fallout should cover extensive areas, Fallovt sempling stations should be located in areas which are nost likely to receive significant fallout. Determimtion of such areas should be made in consultation with those who are responsible for deciding what weather conditions are required to detorate a 101