and the fallout was directed northward, intercepting the anchored lagoon stations and the
northern islands. The close-in fallout pattern is illustrated by the data points and es
timated contours in Figure 3.7.
Since the yield of the detonation was only 130 kt, this
pattern represents a large fraction of the total fallout.
One gamma-rate record was obtained fromSite Dog, indicating a decay exponent of
residual radiation between 1.1 and 1.25. The fallout arrived at about H + 20 minutes,
and a maximum exposure rate of 23 r/hr was observed at H + 40 minutes. The integrated
exposure till H + 15 hours was 51 r.
3.3.5 Shot 4. Most of the Bikini Atoll stations did not receive appreciable fallout
during Shot4. The shot location and the winds localized the radiation levels of military
Significance to the northeastern portion of the atoll. Land readings and contours derived
from sample counting and Rad~Safe surveys are illustrated in Figure 3.3 for the atoll
area only.
A gamma-rate record from Site George, about three miles from ground zero, indicated
a time of arrival of 20 minutes, a peak exposure rate of 670 r/hr at H + 40 minutes, and
a decay exponentof 1.4.
3.3.6 Shot 5. The only close-in data available for Shot 5 are from Rad-Safe surveys.
The extensive downwind fallout pattern was documented for the first time by a combined
water-surface survey, aerial survey, and water-sampiing operation. The results of
these surveys are represented in the contours of Figure 3.9, in which the dashed contours
near the atoll have been drawn by interpolating between the survey results and the RadSafe data.
3.3.7 Shot 6.
The pattern on the northern end of Eniwetok Atoll was documented by
counting fallout samples frm land and raft stations, and by Rad-Sa/e surveys on land.
The aerial survey operated north of the atoll to determine contours, and two tugs gathered water samples throughoutthe fallout area. Analysis of the water samples, combined
with an estimate of the depth of mixing, served to determine the land-equivalent exposure
rate at a numberof points; the aerial survey served to fill in the contours.
are illustrated in Figure 3.10.
3.4
The results
PHYSICAL AND CHEMICAL CHARACTERISTICS CF FALLOUT
Samples from the land~surface Shots 1 and 3 generally contained both solid and liquid
components, although the liquid could have been due in part to rain and ocean spray. The
solid component consisted mostly of white, opaque, irregularly shaped particles. The
water-surface Shots 2, 4, and 6 produced predominantly liquid fallout, with some solid
particulate observed after Shot 6. An appreciable part of the activity from water-surface
bursts was probably in the form of an aerosol, which produced high activity levels on
identification flags of the floating stations after Shot 2.
The particle-size distribution of solid fallout during Shot 1 at Bikini Atoll and at the
distant atolls is summarized in the form of integral distributions on a log-probit plot in
Figure 3.11. The data appear to fit long-normal distributions with different mean sizes
and standard deviations for the different downwind distances.
Between 92 and 98 percent of the activity from land-surface—burst fallout was as-
sociated with solid material, but only 25 to 40 percent of the activity from the barge shots
was not in solution. The pH of the land~surface —burst fallout was between 9.0 and 12.3,
48