Chopter | INTRODUCTION 1.1 OBJECTIVES The objectives were to: (1) survey the gamma radiation fromfallout-contaminated ocean areas using an airborne detector and (2) make air-absorption measurements So that the data from the airborne detector might be related to the dose rates at 3 feet above the sea. 1.2 BACKGROUND During Operation Ivy, the USAEC Health and Safety Laboratory (HASL) carried out a program of aerial surveys of the islands outside the Eniwetok Proving Ground (Reference 1). No major fallout occurred on any of these land surfaces. Traces of contamination were clearly discernible fromthe air, indicating the feasibility of aerial surveys. However, with the meager basic data then available, it was not possible to determine whether the contamination from a multimegaton shot, namely, Shot Mike, was primarily deposited as local fallout or remained in the upper levels of the atmosphere. A similar programof aerial surveys was organized for Operation Castle (Reference 2). It was expanded to include monitoring installations at certain selected islands outside the Eniwetok Proving Ground. Shot 1 deposited appreciable fallout on the monitoring installation at Rongerik. Although heavy fallout was thus documented from a multimegaton shot, no estimate of the total quantities of contamination in local fallout could be formed. Succeeding shots in this series deposited little contumination on any of the islands. Just before Shot 5 during Operation Castle, it was found that fallout material remained suspended in the sea. Radiation detectors were hurriedly mounted in aircraft, and the ocean was surveyed following Shots 5 and 6. The work was necessarily limited by the lack of special radiation detectors, sufficient personnel, and aircraft. Because only one aircraft was available, the Survey was confined to the area between 20 and 100 miles from ground zero. However, the rough estimates based on this survey data indicate that each of these shots contaminated about 4,000 mi? with some what-less than half of their total fission yield (Reference 3). The experience during Operation Castle indicated special problems that would arise in aerial surveys, particularly in surveys over tue ocean, Navigational correlation would be difficult to achieve over the open sea on long flights. One aircraft could not cover the widespread areas contaminated after megaton-range shots. Isodose data could not be reduced in the aircraft, although required immediately during the flight period to control the aircraft’s flight pattern. Barometric altimeters are not accurate enough to provide the close altitude control necessary for relating readings of radiation to an equivalent surface level. And lastly, the radiation detec- tor would need special characteristics for the aerial-survey operations. The detector would need a fast speed of response, shielding to minimize the contribution of aircraft contamination to the readings, and independence from the aircraft supply of power for any critical section of the detector. The voltage from the aircraft generators varies over wide limits, and regulation must be added separately. Also, it would be highly desirable for the detector to have a logarith-