In view of these short-term fluctuations, it was necessary to establish a current pattern for
the time period covered by the oceanographic fallout surveys following each shot. Because of
the scarcity of current measurements during the fallout surveys, it was not possible to establish
a pattern from the direct measurements. Instead, the shift of sharp boundaries and hot spots,
over the 4-day period of each survey, were used to deduce a current pattern. By plotting the
anomalies in radiation intensities for each day of the survey, and noting the distance and direction of shift, a fairly clear picture of the currents could be deduced over the entire fallout area.
Whenever possible, the results of the Project 2.64 aircraft surveys were also used in determining boundaries shifts (Reference 9).
The current patterns deduced in this manner for each of the shots are shown in Figures 2.25
through 2.28. Here the current streamlines are presented. A particle of water would follow
the path of the streamline and would move with the indicated velocity.
2.6.10 Corrected Ships’ Tracks.
In order to determine the geographic location and shape of
the original fallout pattern, the pattern obtained from the 4-day survey must be corrected current drift.
The fallout-arrival time has been estimated tor each shot, and the time of each observation
is known.
The difference between them is the length of time that the observed water, at a given
location, has been subjected to current drift. To correct for this drift, the original ships’
tracks (Figures 2.6 through 2.9) were overlaid on the deduced current pattern for each shot and
shifted back along the streamlines an amount corresponding to the current velocity multiplied
cee eeerenemmepaemerparannpeneaten ma a ee
by the time difference between fallout arrival and observation.
In essence, this is what has been done for each shot.
Actually, the procedure is complicated
by the fact that a shift in position results in a change in the deduced time of arrival.
It is neces-
sary to make the current correction, for each position, by trial and error So that the final location anf fallout arrival time correspond.
The corrected ships’ tracks are shown in Figures 2.29 through 2.32 and represent the tracks
the ships would have taken had the measurements been made at the time of fallout. These also
represent the tracks that three vehicles would have made in taking the same survey had the fallout occurred on dry land.
2.6.11 Water Sampling. The method of collecting water samples has been described in the
sections concerning instrumentation and operations. A summary of the sampling program for
each shot is listed in Tables 2.6 through 2.9. The type of sample is listed along with time and
date, position at which sample was collected, position of sample at time of fallout as deduced
from the corrected ships’ tracks, and probe reading of surface water at time of collection.
The probe reading has been corrected for instrument contamination in each case.
The water samples were delivered to Projects 2.63 and 2.64 on the fifth day after each shot.
The results of analyses are presented in the final reports of these two projects.
2.6.12 Decay Constants. The M/V Horizon’s decay tank has already been described in the
section covering instrumentation, The results of the measurements are shown graphically in
Figure 2.33.
The constant calculated is the exponent of t in the equation AL = A,t"* where Ay
is the dose rate at time t after detonation and A, is the dose rate H+1.
A decay tank similar to that installed on the M/V Horizon was aboard the YAG 39.
The dif-
ne ee
ferences between the design and operation of the tanks were: (1) the tank on the YAG was 6 feet
high and 6 feet in diameter, as compared to the Horizon tank (which was 5 feet high and 5 feet
in diameter); (2) the YAG ‘ank was filled with clean water prior to the shot, and fallout was collected as it fell, instead of being pumped in with water from the sea after completion of fallout;
and (3) the sample was not gelled but merely acidified and stirred.
Examination of the results of the YAG 39 tank measurements as shown in Reference 7 shows
the following best-fit straight-line values for k: Zuai, k = -0.86 from H + 25 to H+50; Flathead,
k = -0.92 from H+12 to H+ 40 (beyond H+40 the slope was less); Navajo, k = -1.40 from H+10
to H+150 (for the original, instrument calibration curve); the results for Shot Tewa were so
26