Operation Castle was an atmosoneric nuclear test series conducted in the
Marshall Islands from March to May of 1954. The most notorious test of the series
was Bravo, a



{1] thermonuclear explosive. The too of the resultant

debris cloud reached to nearly 35 km at stabilization time.


Because of an unexpected shift in mid-tropospherie wind directions following







of heading in the predicted

northeast direction, had an easterly alignment. As a result, persons on the atolls of
Rongelap and Rongerik were exposed to relatively high levels of fallout from the
nuclear explosion.

Prompt action was taken by U. S. Task Foree personnel to

evacuate the natives of these islands. Some of the natives on Rongelap, the closest
to the detonation point, suffered temporary nausea and minor skin burns.


exhibited any medium or long term effects from their exposure.
However, after about 10 years, those Rongelap natives, who were young
children in 1954 developed non-maligment nodules on their thyroid glands.


then the occurrence of similar nodules among the Utirik natives has been reported.
The rate of occurrence has been higher than would be expected statistically. The
purpose of this report is to calculate deposition and surface air concentration plots,
using a three-dimensional particle-in-cell suite of codes to estimate the doses at the
islands from which the natives were evacuated. We will also consider the dose from
rainout as part of the debris cloud crossed the atolls.

Finally, the calculated time

nistory of air concentrations on the downwind islands will be presented for several

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