Chopter 2
OCEANOGRAPHIC FALLOUT SURVEY
2.1 OBJECTIVES
The objectives were to: (1) Obtain information on the distribution of radioactivity horizontally
and vertically in the ocean, which together with results of other projects would result in an
understanding of fallout at sea and permit a reconstruction of fallout over an equivalent land
surface; (2) collect samples of radioactive water and other data for this and other agencies and
projects; (3) relate the penetration of fallout into the sea to known parameters such that future
surveys could be carried out with reduced effort; and (4) utilize radioactivity from bomb debris
toward a better understanding of basic oceanographic processes.
2.2 BACKGROUND
In discussions following Shot 1 of Operation Castle, it was conjectured that mixing of the fine
bomb debris might not proceed rapidly into and below the thermocline but would tend to be retained in the mixed surface layer. This conjecture implied the possibility that detectable levels
of radioactivity would persist in the surface layers of the sea for a sufficient time following the
detonation to permit surveys by surface craft. The conjecture was confirmed when ships re~
ported detectable levels of activity accumulated in their evaporators during passage of adjacent
Sea areas.
In the intershot period following Shot 1 of Operation Castle, members of the Scripps staff in
the EPG constructed several experimental Geiger counters for use in shallow water and performed
cursory examinations of water activity in Bikini Lagoon.
The background then existed for an attempt to survey radioactive fallout, utilizing the ocean
surface as a collector and surface vessels as instrument platforms.
In this connection, a Special study was initiated just prior to Shot 5 to obtain an estimate of
the fallout contours by water sampling and by the use of oceanographic survey techniques in the
Open ocean. The results of the survey following Shot 5 and of the water-sampling program following Shots 5 and 6 have been published (Reference 2).
During Operation Wigwam, the same type of survey was again carried on by SIO (Reference
3). The notable difference from Castle was that no fallout was anticipated, and the task was one
of outlining the radioactive water mass and of following the transport of this water by the ocean
currents. For this survey, new and improved underwater Geiger counters were utilized.
The results of the latter phases of the Wigwam survey (Reference 3) indicate that the survey
techniques successfully located radioactivity in the water that was only 10 to 20 gamma counts/
Min higher than the natural background count of oceanic water.
2.3 THEORY
The use of the ocean as a collecting surface has one singular simplicity: there is no doubt as
to the efficiency of its collection, since each unit surface area retains whatever falis onit.
Beyond this, the oceanographic survey approach is subject to the complexities of the fluid
medium, and dispersive processes begin immediately following the arrival of fallout.
wateot in very high latitudes, there exists in the ocean a surface layer of relatively warm
€t that varies in thickness, depending upon its geographic location. This thickness may
Tange from less than 30 to more than 150 meters. The temperature of the water in this layer
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