which commenced about 1015, 5 May following!YANKEEand did not materially interfere
with the work carried on by the Section.
5.4.2
Discussion
1. Lagoon and drinking-water samples: After the AW levent it became evident that recovery programs and preparations for future detonations at Bikini Atoll could only be accomplished by personnel working from ships anchored in the lagoon. Each detonation resulted in
the lagoon water being contaminated; the magnitude and persistence of the contamination
depended on the yield and location of the shot with respect to the anchoragesites.
A program was initiated by the TG-7.3 Rad-Safe Officer to pick up daily samples, both
from the surface and 90 ft below the surface, at various points in the lagoon. The samples
were turned over to the Radiation Analysis Section, where the specific beta activity in microcuries per milliliter was determined. The purpose of the program wasto protect the ships
from the accumulation of hazardous amounts of radiation when anchored. The maximum concentration encountered in the lagoon anchorages was 8.4 x 1078 pc/ml. The average activity
varied from 1 x 10 c/ml to 3 x 10 pe/ml.
Also of interest was the drinking water on the ships since it was derived from the distillation of the lagoon water in the ships’ evaporators. The possibility of carrying radioactive particulate matter into the fresh-water output existed, especially on board ships used primarily as
hotel accommodations. Accordingly a program was set up by which ships turned in samples of
drinking water and tntake water from the lagoon on at least a daily basis. These samples were
: also analyzed for beta activity in microcuries per milliliter. No drinking water on board the
ships was found to contain any appreciable radioactive material. In view of the fact that the
activity found in the lagoon water was associated with the sedimentleft after evaporating the
water, it was not surprising that the drinking-water samples derived from the condensation of
water vapor from a distillation process contained no activity.
As the operation progressed it became evident that excessively contaminated water could
be observed visually as a result of the sediment being deposited in the water and could be
evaluated adequately using only a PDR-39 survey type meter operated from a helicopter hovering over the surface of the water. As a result of using this technique, following the AV?
a
event the numberof lagoon samples to be analyzed was reduced considerably and moretime
could be devoted to more pertinent problems (see Fig. 5.1).
In addition to the drinking-water samples from the ships, drinking-water samples were
analyzed from Rongelap, Kwajalein, and Uterik islands. The initial samples from Rongelap
were collected at the time the natives were evacuated from the island on 5 March and followed
to the end of the operation for decay characteristics. The specific activity of these samples
indicated that the water was contaminated from 2 to 25 times above the AEC operationaltol-
erance of 5 x 107 yc/ml. A representative decay curve for one of these samples is shown in
Fig. 5.2. No appreciable activity was found in the samples from Kwajalein Naval Station. Samples taken on the survey trip to Rongelap and Uterik islands indicated an average specific activity of 1.4 x 1075 pc/ml and 2.1 x 10+ yc/ml, respectively. Two samples from Rongelap contained no activity and are not included in the above values.
2. Air sampling: Portable air samplers, capable of drawing 0.65 cu ft of air per minute
through a 6-in. filter paper, were used on the initial survey flights following each event and
during those periods when fall-out occurred on board ship. With the instrument on for 15-min
intervals during the fall-out period, a continual check could be made as to whether fall-out was
still occurring and at least a qualitative estimate could be made of the order of magnitude of
the concentration of the radioactive contamination in microcuries per cubic foot of air. Using
such a large-sized filter paper necessitates folding the paper twice in order to place it on the
bottom of a large lead pig. Only gross counts per minute were obtained in counting. After these
initial data were taken, however, a small portion of the filter paper was mounted on a brass
planchet and followed for a period of time in order to obtain thedecay.characteristics of the
sample. The decay curve for two such samples, collected after, fhtoa)
\and ViMuece. are
shown in Fig. 5.3. The air samples collected on 1 March, when the USS Bairoko received a
46