106 Health Physics August 2010, Volume 99, Number 2 Pacific during World War II. After World War II, the United States established the Pacific Proving Grounds for testing nuclear weapons. From 1946 through 1958, 65 nuclear weaponstests, in seven series, were carried out by the United States at Bikini and Enewetak Atolls located at the northwestern end of the archipelago that makes up the Marshall Islands (Fig. 1) and one additional test was carried out 100 km to the west of Bikini. The total explosive yield of the 66 tests was approximately 100 Mt (equivalent to 100 of the 66 tests that were carried out in or near the Marshall Islands resulted in measurable fallout in the Marshall Islands (Table 1). Of special significance wasthe largesttest conducted in the Marshall Islands, code-named Castle Bravo, a 15-Mt thermonuclear device tested on 1 March 1954. As a result of unexpected wind shear conditions, heavy fallout of debris from Bravo on atolls east of the Bikini Atoll test site resulted in high radiation doses to the populations of nearby atolls. While the populations of Bikini and Enewetak were relocated before the testing began, other populations were evacuated following the Bravotest. Within about two days following the detonation of the Bravo test and the unexpected fallout on atolls to the east, the resident populations of Rongelap (including some Rongelap residents temporarily present on Ailinginae) and Utrik, as well as American military weather observers on Rongerik, were evacuated to avert continued exposure, million tons of trinitrotoluene or TNT) (U.S. DOE 2000; Simon and Robison 1997; Simon 1997), about 100 times the total yield of the atmospheric tests conducted at the Nevada Test Site. Radioactive debris from the detonations, dispersed in the atmosphere, was generally blown by the predominantly easterly winds towards the open ocean west of the Marshall Islands, though various historical reports (e.g., Breslin and Cassidy 1955; DNA 1979) indicate that radioactive debris from a numberoftests traveled in other directions. The radioactive debris generated by thetests that eventually fell to the ground is termed fallout and was the single source of the exposures of the Marshallese people described in this report. According to our analysis, twenty to be decontaminated, and to receive immediate med- ical care for conditions of acute exposures (Cronkite et al. 1997). Nucleartest site_atolls °°“)> Seienaton ste 164° . a Bikini 4)Q_ Rongerik > following BRAVO x Ujelang detonation : . “* SS “eo, @ J Te oO. ey “4 ~% Lib Island —>\Wolje q. Y Erikub- 4. ep \ a ey Island Island pe # ' Mejit “demo ») 2, <—~* St ae ) Lae ixiep > Ailuk (my Sa Kwajalein = <a o Taka = Islands evacuated —_ oui ; 172° Utrik Ailinginae%» b& a Woth or "Bikar 168° Rongelap - oa Enewetak ‘ eo AON | Aur Jabwot e =A) 7 %p = Ailinglapalap The Marshall Islands » Jaluit 3 f Ame D> SF Majuro i AS : Namorik 168° ~. Knox Kili Island Ebon S 172° Fig. 1. Atolls and reef islands of the Republic of the Marshall Islands, and locations of nuclear test sites and of evacuated populations.