APN ae ii The emphasis on transuranics in the cleanup operation alsojwas influenced by the fact that Pu-239 has a half-life of 24,000 ypars whereas Sr-930 and Ce-137 have half-lives of about 30 years. near future, however, the fission products must be of great I the cern because of their rapid rate of movement through the soil and tReir very active i.:corporation into the food chain. Since there was virtually no contamination on the southern| islands, it was planned that only these islands would be settled at the] begin- ning. Occupation of the northern islands after cleanup was tolbe postponed until radioactive decay brought the concentrationsof Sr-90 and Ce-137 to acceptable levels. 3.5 Location of the Contamination Before work could begin it was necessary to find out which] islands were significantly contaminated and to identify the specific pjaces where remedial work would be required. As has been explained, ithe cleanup was concerned with the transuranics, mainly plutonium, [but plstonium emits only an alpha particle accompanied by a very 1 x-ray so it is not practicable to measure it in the field. the plutonium is associated with americium, which has a suffic penetrating gamma ray for detection through several inches of Aerial surveys and in-situ monitoring detected the significantly contaminated islands and specially designed detection equipment on a tracked vehicle then was used for a detailed survey. Rea were taken at every intersection of a 50-meter grid. Soil samples at various depths were taken at each intersection for laboratory to determine the plutonium/americium ratio. In areas of high ination, samples were taken at. 25-, 12.5-, and 6.25-meter inte This work provided the basis for radiation contour maps that used by the cleanup crews. 3.6 Nature of the Problem The cleanup problem was not confined to surface soil con with transuranics. During the weapons testing program, debris tests frequently was cleared from a site and dumped in an old in preparation for reuse of the site for additional tests. Al detectable dumps, crypts, and burial sites were excavated and radioactive contents transferred to the Cactus Crater. Old bl houses, sunken barges, and Landing craft in less than 15 feet and other miscellaneous debris were collected, monitored, and of in the containment structure, if contaminated, or in deep p the lagoon if not contaminated. Retrieval from dumps often was difficult and a crypt on Island was so extensive that a year was required to plan and its excavation. About 16,00U items from World War II (unexpl artillery and mortar shells, hand grenades, small arms, and also were detected, dug up, and detonated or removed by Navy Ordnance Disposal Teams. After the rubbish was removed, the t inches of soil was scraped off, loaded into barges, and trans Runit Island.