INTRODUCTION
Operation Castle was an atmospheric nuclear test series conducted in the
Marshall Islands from March to May of 1954. The most notorious test of the series
was Bravo, a 15 megaton
(1) thermonuclear explosive. The top of the resultant
debris cloud reached to nearly 35 km at stabilization timel!
Because of an unexpected shift in mid-tropospherie wind directions following
detonation of Bravo, the fallout pattern, instead of heading in the predicted
northeast direetion, 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 Force 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.
None
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. Since
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 caleulate 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
history of air concentrations on the downwind islands will be presented for several
nuclides.