wy o = sure problems. t Surface and near-surface bursts pose larger potential radiation expoThese bursts create more radioactive debris because more material is available for activation within range of the neutrons generated by the explosion. In such explosions, the extreme heat vaporizes device materials and activated Earth materials as well. These materials cool in the presence of additional material gouged out of the burst crater. This extra material causes the particles formed as the fireball cools to be larger in size, with radioactivity embedded in them or coating their surfaces. The rising cloud will lift these particles to altitudes that will depend on the particle size and shape and the power of the rising air currents in the cloud, which in turn depend on the energy of the burst. The largest particles will fall back into the crater or very near the burst area with the next largest falling nearby. It has been estimated that as much as 80 percent of the radioactive debris from a land-surface burst falls out within the first day following the burst (Reference 2). Bursts on the surface of seawater generate particles consisting mainly Of salt and water drops that are smaller and lighter than the fallout particles from a land burst. As a consequence, wdter-surface bursts produce less early fallout than similar weapons detonated on land. The large-yield surface bursts in the PPG over relatively shallow lagoon waters or on very little truly dry land probably formed a complex combination of land-surfaceand water-surface-burst particle-size characteristics. Several surface detonations at the PPG were of such a large size that they formed underwater craters. These craters retained a fraction of the weapon's radioactive debris and activated materials. The water that over- lay these craters acted as a shield to protect surface operations from the radiation from this material, but it also provided a means for the material to move from the craters into the general circulation system of the lagoon waters. The craters were subject to washing and silt plumes were observed to come from them for long periods after the shots; it is reported that plumes from the MIKE crater were visible a year after the detonation (Reference 3, p. 207). 30 (Cu ,»