q . - . . . This report is an addendum to the final report of Project l.1l, Operation CASTLE, Its purpese is to consider the physical factors and dosimetry of the fallout on the Marshall Islands from the first . 4 | - ABSTRACT . : shot of Operation CASTLE, Data was summarized from fisld Radiological Safety surveys, fallout radiochemical studies, and rallout gamma spectral measurements, The influence of these and other factors on an evaluation of survey meter response and to+4l dose estimates was considered, Estimates of fallout duration times and energy distribution of the dose from a plane sourca were macs and tha effect of diffuse source-geometry on the depth-dose to air-dos2 relationship was considered, Superficial doses fron soft ganna and beta radiation were also considered, Sincs the fallout incident created an initial emergency during which data collection was of secondary importance, attenpts to recon- struct the event have been uncertain, Much of the data was indicative rather than exact, However, a fairly consistent estimate of external gamma dosage was pessible, although tne question of beta exposure renaing mostly unanswered, It nas been assumed that no significant neutron or alpha particle exposura ocaurred, Internal doses from in= haled or ingested material and the bicemedical aspects of the incident have been discussed in other CASTLE Project h.l reports, It was concluded that: j - j j (1) the AaN/PDR-39A requires a correction factor of about plus 20 percent in dose-rate readings made under the conditions described; (2) decay of the rad gactivity of the fallout is believed expressible by the factor of T~O 3 (3) the external gamma dose was delivered primarily by radiation entrgies of 100, 700, and 1500 kev; (4) the beta dose was delivered by beta radiation of maxinun energies of 0,3 and 1.8 Mev, mostly from fallout deposited on the skin itself; (5) the exposures cocurred between 4 and 78 hours after the detonation = the fallouts were probably of 12-hcurs duration; (6) diffuse source geometry increased the midline dose by about 50 percent conpared to the midline dose which would have resulted from a bilateral narrow bean exposure of the same air-dose; (7) error in the estinates is believed to be less than 50 percent; and (8) total air gamma doses were estimated as follows: 81 r; and Utirik, 13 r. Rongerik, 86 r; Rongelap, 182 r; Ailinginae,