was in highly radioactive water.
The ship was only allowed to the edge of the highly radioactive
water, then turned out away from this water. By the use of this method, the ship remained
fairly free of contamination: Vertical casts were made just outside the highly radioactive water
,
along its edge.
water samples were taken at various intervals for later determination of the radioactivity,
These were taken at the surface and at various depths.
3.5 INSTRUMENTATION
The surveys were carried out aboard an LCU. An underwater radiation detector (probe) wags
‘used to survey the radioactivity in the lagoon. This instrument was discussed in Chapter 2. No
recorder was used on the LCU. The readings were presented on a microammeter and recordeg
on data sheets by the Scientist, as required. For surveying in contaminated water having a dose
rate too high for the low-level probe, an AN/PDR-27C hand set was used on deck. This type of
measurement gives qualitative results that permit a rough presentation of the fallout zones,
3.6 RESULTS AND DISCUSSION
3.6.1
Shot Cherokee.
No radioactive water was found on shot day, and no further measure-~
ments of radioactivity were made for this detonation®
3.6.2 Shot Zuni.
The fallout pattern for shot day is sketchy.
The probe became inoperative
afterfirst stations. The stations that were occupied during the next few days indicated
that the fallout immediately following the detonation covered the entire lagoon, except for a
small zone roughly between Sites Nan and Oboe.
On Zuni plus 1 day, the most radioactive water (25 to 100 mr/hr’) was found from the shot
site westward in a narrow bandto the eastern edge of Site Victor (Figure 3.1). By Zuni plus 2
days, the radioactivity of the water at the shot site was 31 mr/hr at the surface and 54 me/hr
at 25 meters. The radioactive body of water off Site Uncle and Rukoji Pass was less than 4
mr/hr at the surface,
At the shot site, the persistence of the radioactivity is, in part, due to
fine radioactive particles washing from the sides of the crater.
At the time of the shot, the ebb tide had just begun. This would indicate that a great amount
of highly radioactive water near Surface zero was expelled from the lagoon as the tide ebbed.
The highly radioactive water was quickly lost from the lagoon by the proximity surface zero
to several passes, the influence by the tide, the westward moving lagoon current and westward
moving ocean current. The lagoon currents from the surface to the bottom flow westward along
the southern edge of Bikini Atoll. These currents carried the highly radioactive water from the
shot site westward to Rukoji Pass, between Site Tare and Site Uncle, where a large amount was
lost at ebb tide. The westward-moving ocean current on the south side of Bikini Atoll carried
all the radioactive water from the lagoon beyond the mouth of the passes so that it could not enter
on the flood tide.
Ona flood tide, D+1 values of 1.2 mr/hr at the surface, and 0.22 mr/hr at
20 meters and below were measured in the pass between Sites Uncle and Tare.
Measurements
taken 1,000 yards to seaward of the pass were 0.24 mr/hr from the surface to 39 meters.
The currents in the lower layers near the edge of the lagoon have low velocities and move in
the same direction as the upper layer. The maximum depth in the pass between Sites Uncle and
Tare is 19 fathoms, but at one location in the pass there is 20 fathoms. These two passes allowed
a large amount of the radioactive water in the lower depths to get to the open ocean. The last
observation taken near the shot site (1,600 yards, bearing 000 degrees) on D+5 indicate that
below the depth of the sill in the passes, the radioactivity of the water was relatively high compared to the water above this depth. The surface was 0.49 mr/hr, at 37 meters the reading was
rn
‘In this chapter, all dose rates are presented as “apparent” mr/hr as defined in Appendix A.
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