that fell through the thermocline.
This is a function of both direction and distance from greund
zero.
4,
Decay constants.
The decay constants used for data reduction are straight-line
averages Of measured values. The measurements were not started prior to 20 hours after each
shot. Examination of other types of decay records shows that decay constants of dose rate change
yery little between H+ 1 and H+50 hours. On this basis, the decay-tank measurements extrapolated to H+ 1 hour are probably reliable.
5. Fallout time of arrival. The time of arrival was determined by combining the
predicted values with actual measurement. The values are probably correct to within a few
hours over most of the fallout area. A 2-hour error in fallout time yields about a 10 percent
error in the final results up to the time mixing is completed.
After that, such an error in time
has no effect in final calculated dose rate and results in an error of a few percents in the total
dose.
6. Current correction. The correction used for drift due to ocean currents was deduced from the day-to-day shift in boundaries and hot spots in the fallout pattern of each shot.
Judging from the crossings of ships’ tracks and the general coherence of the pattern as a whole,
the current corrections used are truly representative of the actual ocean currents.
7. Conversion from in-situ to 3-foot dose rate. The factor that was used to
convert the probe reading in the water to the dose rate at an elevation of 3 feet is derived in
Appendix A.
The lack of knowledge of the energy spectra limits its accuracy.
If the assumption
of energy Spectra during the fallout surveys is valid, this factor has an estimated accuracy of
+15 percent.
2.6.17 Cherokee Surveys. The measurements taken following Shot Cherokee were not reduced. Only one small spot of water, 2 miles wide and of unknown length, was detectably above
the oceanic background. The survey ships ranged as far as 300 miles from ground zero, but
were unable to detect any other measurable fallout. The ships’ tracks are shown in Figure 2.5.
2.6.18 Zuni Surveys. The first shot of the series that produced a measurable amountof
fallout was Zuni. All tnree survey ships became contaminated by direct fallout during the early
Stage of the survey. This made low-level ship-board calibration checks impossible, but the calibrations at levels of above 30 mr/hr were sufficient to give confidence to the measurements.
Theshot was detonated on land atSite Tare on 28 May 1956 at 0556 M. Thetotal yield was 3.38
Mt,|
_
Much of the fallout was associated with solid particles large
enough to penetrate below the thermocline. This is evident from the penetration measurements
taken by the Project 2.62 YAG’s.
The portion of fallout that penetrated below the thermocline is unknown and is indeterminable
from these measurements. Rather than attempting to estimate the percentage, these results
asSume no penetration beyond the depth of mixing. Using this assumption, the iso-dose-rate
contours of fallout from Shot Zuni at H+1 hour are shown in Figure 2.36.
These are the dose
rates that would be received at a height of 3 feet had the fallout occurred on dry land instead of
in the ocean. The areas, in square miles, enclosed within the contour lines of Figure 2.36 are
listed in Table 2.11, in which th€total and fission yield is presented for comparison between the
different shots.
The total dose that would be accumulated between time of fallout and H+50 hours is shown in
Figure 2.37 for Shot Zuni, and the areas enclosed by these contours are presented in Table 2.11.
2.6.19 Flathead Surveys.
0626 M on 12 June 1956. |
Shot Flathead was fired overwater from a barge offSite Dog at
Very little
Of the fallout should have been associated. with solid particles large enough to penetrate below
the thermocline. The H+1 hour iso-dose-rate contours are presented in Figure 2.38 and the
’ccumulated total dose to H+50 hours is shownin Figure 2.39.
both these figures is listed in Table 2.11.
29
The area within the contours of