Section 2 RADIATION ENVIRONMENTS Since an understanding of the radiation environments encountered by the ships participating at Operation CASTLEis essential for the dose reconstructions that are presented in section 4, the discussion thereof in Reference 1 is repeated and augmented. With the exception of the operational activities of PC-1546, LST-1146, and MOLALA, activities conducted in conjunction with project support requirements by the remainder of the ships discussed herein, occurred primarily within the confines of Bikini Lagoon. Figure 2.1 depicts the areas within the lagoon where the ships were required to spend most of their ume during the operation. Areas Nan (off Eneu Island) and Tare (north of Eneman Island) were the primary anchoragesforall of the task force ships throughout the operation. Areas Charlie, Dog, Fox, George, and Howin the northern lagoon, were visited during technical project support activities. 2.1 RADIOACTIVE FALLOUT. All of the ships addressed in this report encountered fallout after one or more of the six CASTLEdetonations. In most instances, particularly where significant fallout was encountered, shipboard radiological data are available to define the topside radiation environment. In some instances, however, shipboard environments mustbe inferred from radiological data obtained on nearby islands, such as the residence islands of Enewetak Atoll. For each ship, an average intensity curve is presented showing the free-field radiation intensity as a function of time after each shotthatresulted in significantfallout. The intensity curves are then time-integratedto yield a daily free-field integrated intensity on each ship through 31 May 1954, whentheroll-up phase was complete. Extensive radiation intensity readings obtained on Bikini Island (Bikini Atoll) following Shot BRAVOindicated decay rates that varied considerably from the traditional t}-? rule (Reference 6). Average values for the decay exponent, obtained from several gammaionization time-intensity meter measurements on Bikini, are as follows: 3 <t < 10hours; k = -1.19 10 <t < 48 hours; k = -0.82 48 < t < 480 hours; k = -1.50 t >480 hours; k = -1.20