our purpose is to consider what is involved, buth in dollar cost and ‘in further environmental insult to the islands, for a man-made cieanup to lower the residual radiolesical expesures presently existing in the ° islands to exposures that are cciiaonly encountered elsewhere in the world in normal human activitics that span lifetimes. Radioactive Isotopes of Concern The principal concerns existing radiologically at Eniwetok Atoll * are presently: * Cesium-137, a 30-year half-life isotope that is a fission product. When present in the top few centimeters of soil, its gamma rays externally result in whole-body exposures for inhabitants. of less importance is the fact that when present on the top surface of soil its beta rays extérnally result in skin exposures. Being chemically similar to potassium, cesium-137 deposits in the muscle of the entire boyd upon entry to the human body via the food chain; the consequent health hazard is then principally the risk of inducing cancer. * Strontium-90, a 29-year half-life isotope that is a fission product. Not being a gamma ray emitter, it externally provides only a beta ray exposure to the skin when present as deposits on the top surface of the ground. Being chemically similar to calcium, it deposits in the bone upon entry to the human body via the food chain; the consequent health hazard is then principally the risk of inducing leukemia.