qt. INTRODUCTION A radiological survey of the islands of Bikini Atoll in the mid-Pacific was conducted in late April and early May of 1967, nine years after cessation of extensive testing of nuclear devices in the area. The survey, sponsored by the Division of Biology and Medicine of the U. S. Atomic Energy Commission, included general observations of the prevailing environmental conditions and a detailed investigation of external environmental radiation levels. Exposure rates due primarily to penetrating gamma radiation were measured, the principal radioisotopes contributing to the total and exposure rate on each of the major islands of the atoll were determined. ~~ Bikini Atoll is located in the northern Marshall Islands. The atoll consists of a number of small coral islands surrounding a lagoon 22 miles long and 13 miles wide. Total land area of the atoli is 2.32 square miles, of which 1.25 square miles comprises the three largest islands, Eneu, and Nam. Figure 1 is a map of the atoll. Bikini, The names of the islands differ on the various hydrographic charts, being usually variations of Japanese renditions of the original Marshallese names. On the map in Figure 1 and throughout this report we have used the Marshallese names of the islands. The testing of nuclear devices at Bikini Atoll occurred during 1946, 1954. 1956, and 1958 and included the detonation of some 23 devices of both fission and thermonuclear types. The locations of the tests and the code name and year of each event are indicated on the map in Figure 1. Most of the shots were detonated on barges anchored in the lagoon or on the atoll reef. Two shots were air drops, Able and Cherokee, two were underwater, Baker and Maple, and three were surface bursts, Bravo, Zuni, and Koon. All of the islands received in varying degrees the resultant radioactive fission and activation products which were spread about the area. Although prevailing winds generally carried the local fallout westward, there were exceptions - notably shot Bravo, unexpected winds carried the fallout toward the east. when