-u. sampling of water at various depths, making tows to gather plank- ton -- the tiny marine organisms which tend to concentrate radio- active materials in their tissues -- and catching of fish for analysis for radioactivity. In addition to these investigations, land and marine biological surveys again will be conducted at Eniwetok and Bikini and other atolls nearby. Samples of water and of plants and animals living in the lagoons and on the reefs and islands of the atolls will be collected and analyzed for radioactivity. Fallout Monitoring in United States The heavier particles fall out of the radioactive cloud at early times after a detonation, while their radioactivity is still high. Therefore, the highest levels of radioactivity occur over a local area downwind from the point of detonation. The area of significant fallout is expected to occur entirely within the uninhabited danger aree surrounding the Eniwetok Proving Ground. As the radioactive cloud is transported away from the point of detonation, it 1s widely dispersed by air currents and diluted by normal air. Its radioactivity also decreases rapidly because of the normal process of radioactive decay.* By the time the cloud from a detonation in the Eniwetok Proving Ground has traveled across a vast expanse of ocean, it will have become thoroughly dispersed into the air and will have lost most of its Original radioactivity. AS a result, the exposures to radioactivity in the United States from the Eniwetok tests are expected to be low. Although levels of many times the normal background may be reached in some localities, these increases will be temporary and will not greatly increase the total exposure to radiation. Average exposures of residents of the United States to radiation from weapons tests during the past five years has been much less than the average exposure to radiation from natural sources during the Same period. Outside of the Pacific area moritoring and sampling activities will be conducted in cooperation with the U. 5S. Weather Bureau, the U. S. Public Health Service, and at Atomic 4 *Padloactive fallout consists of a mixture of radioisotopes, with varying half-lives. The mixture as a whole decreases in radioactivity in such a way that for every seven fold increase in age, she total radioactivity is decreased 10-fold. Thus, the radio- activity at seven hours after H+1 hour is only one-tenth that at H+1 hour, and in 49 hours is one-hundredth, etc. (more)