es ee ee
cistern opening measured about 0.65 m and was fed by means of galvanized metal
sheeting used for catching rainwater (Figure 12). A little rain was reported on
the afternoon of March 1, 1954 (Sh57). We assumed that the additional cistern
catchment area did not contribute water or activity to the cistern.
Results of the analysis for gross beta-activity concentration in
clears water ranged from 1.8 x 10° to 2.0 x 10° Bq a (0.005 to 0.054 uci
1) with a mean of 5.0 x 105 Bq 27! (0.027 uci mi!) at 50 hours post-
Getonation (0C68). The fallout from Castle series coral surface bursts
including BRAVO was reported as being barely soluble in water (Ka66). BRAVO
fallout, which was collected with mixtures of rain and sea spray, lost only 20
to 50% of the iodine activity to the liquid phase (Ka66).
The serviceman at
Rongerik Atoll examined the terrestrial fallout under a microscope and reported
that the sand-like granules were not soluble in water on the microscope slide
(Sh57). Therefore, most BRAVO activity and a good portion of the radioiodine activity probably remained with the fallout particles at the bottom of a cistern.
We extrapolated the 50-hour post-detonation beta-activity concen-
trations back to 0.5 day post-detonation using decay characteristics for Bikini
ash components.
The range for gross beta~activity concentrations was 1.0 x 1
to 1.2 x 107 Bq 2-l (0.027 to 0.31 uCi mi!) and the meanwas 2.9 x 10° Bq 2
(0.078 wCi ml~*). At 0.5 day, a total of 3.7 x 19019 5
2 (1 Ci m2) of Bikini
ash gross beta activity was estimated by us as the sumWE the activity of all nu-
clides listed in Table 13.
Given the area of a cistern opening, we calculated.
that the average cistern contained 8.3 m? of water if all the Bikini ash activ-
ity was in the liquid phase.
This water volume would be necessary to dilute the
activity to the level reported by the radsafe team. We estimate that this was
about 55 times greater than the observed water volume of the cisterns as pre-
viously indicated by Sharp (Sh57).
Assuming only 20% of the iodine activity in
Figure 12. A cistern at Rongelap Island.
- 41 we
a
be
em
Pd
Pe
RE
Ow
webu Ls