obtained with several gamma ionization time-intensity meters on Bikini (Reference 11) are as follows: 3< t <10 hours; k = -1.19 10< t <48 hours; k = -0.82 4&8 < t <480 hours; kK = -1.50 t > 480 hours; k = -1.20 A varying decay of this type is consistent with the presence of Np-239 (ty, = 56 hr) and U-237 (ty =160 hr), which are both generated in significant quantities fro:n neutron Capture in uranium. After several half-lives, when the presence of these two radioisotopes no longer dominate the decay rate, it approaches the traditional rie value. In the absence of radiological survey data, the time-dependent decay rate is used in reconstructing the radiation environments on the ships and atolls covered in this report. Generally, radiologicat data on the residence islands of Enewetak and Kwajalein support a t7!-5 decay rate between 48 and 480 hours after detonation; shipboard data indicate slighily greater decay rates (t™ period. 16 5 471-9) during the same The steeper shipboard decay rates can be attributed to a combination of the increased effectiveness of "weathering" on a ship's surfaces (as opposed to island soil), and to decontamination being carried out onboardtheships. All of the ships addressed in this report encountered fallout following one or more of the six CASTLE detonations. In most instances, particularly where significant fallout was encountered, shipboard topside radiation environment. radiological data are available to define the In some instances, however, shipboard environments must be inferred from radiological data obtained on nearby islands, such as residence islands of Enewetak and Kwajalein Atolls. the For each atoll and ship, an average intensity curve is presented showing the free-field radiation intensity as a function of time after each shot that resulted in significant fallout. The intensity curves are then time-integrated to yield a daily free-field integrated intensity for each atoll/ship through 31 May 1954, when the roll-up phase was nearly complete. The water in Bikini Lagoon also became contaminated following several of the five detonations conducted there. As ships steamed or anchored in the contaminated 27