fallout with particle size, zero-point environment,
and time and distance of collection; (2) the chemical
and radiochemical nature of liquid fallout; and (3) the
manner in which decay rates are affected by varia-
tory; E. R. Tompkins, Project Officer.
The objective was to determine the chemical,
physical, and radiochemical nature of fallout from
Castle. This information is useful in deducing the
mechanism of contaminant formation, evaluating
radiological situations, developing radiological
countermeasures, and interpreting field tests of
countermeasuresat Castle.
Shot 1 produced a dry fallout. Samples from
Bikini Lagoon and land stations, and from islands in
atolls 8 to 120 miles distant were obtained and analyzed. The fallout from Shots 2, 4, 5, and 6 were
chiefly liquid in the form of an extremely fine mist
of aerosol. Samples from free-floating buoys, lagoon and land stations, and from the Project 6.4
YAG’s were analyzed for these events. Because rain
was falling during the period of fallout after Shot 3
(detonated on Tare:, the material collected was a
slurry. Water samples from the open sea were collected out to 200 miles from ground zero for Shots 5
and 6.
The gammacountof fallout sampies from Shots 1
and 3 war found to be associated with rhe solid fraction to the extent of 92 to 98 percent; for Shots 2 and
4 the solid fraction contained 25 to 38 percent of the
gamma count. The remainder was found to be contributed mainly by emittera in the ionic state.
Neptunium was found as 65 +11 percent Np (IV) as
averaged for Shots 1, 2, 3, and 4; the remainder was
found as Np (V + VI).
Iodine was found in the solid fraction of the fallout
from Shots 1 and 3; it was also found in the liquid
fraction of the fallout from Shots 2 and 4. In every
case, iodine appeared to be essentially in the ~1
oxidation state.
Quantitative analyses were made on all samples
recovered from Shots 1, 2, 3, and 4. Island coral,
lagoon seawater, and lagoon-bottom materials were
also analyzed.
tions in radiochemical composition.
The investigation of radiochemical properties of
fallout were conducted in Bikini Atoll and Bikini Lagoon. The adverse effect of mixing upon the liquid
and solid fallout was minimized by a new collection
system which immediately separated the phases.
Approximately 20 percent of the activity in the
fallout from Shot 1 was associated with particles
smaller than 10 microns. <A trend of decreasing
specific activity with increasing particle size was
found in Shot 1 fallout below 50 microns. Fractionation of figssion~product nuclides was found on Shots 1
and 3. Gross decay of Shot 1 fallout generally follow-
ed the equation I = kt™*-°, and did not vary with particle size.
There was evidence of an unusually high
Mo’? fission yield on Shot 1.
In order to predict the military effects of fallout
from operational nuclear weapons, it was necessary
first to understand the basic dependence of these
phenomena on environmental and weapon character-
istics. Different effects are to be expected from
land and water detonations than from shots on the
surface and below the surface, from various soil
types, and from different depths of water. Rainout
may exert a considerable influence on the significance
of ground contamination. The experimental nuciear
devices in Castle were detonated in peculiar zeropoint environments which will be absent in the case
of most operational weapons detonations.
Project 2.7 “Distribution of Radioactive Fallout
by Survey and Analysis of Contaminated Sea Water”
The yields of U"" and u™*, as well as that of U™,
were sufficiently high to contribute significantly to
the residual contamination radiation and to affect the
gross beta- and gamma-~decay curves.
Analyses of al) absorption curves show the presence
of beta energies ag high as 2.6 Mev at H + 15 hours
(Shot 4), with the maximum beta energy decreasing
to about 2 Mev at H +3 toH +10 days. Lead absorption curves were analyzed into three apparent energies: 0.15 Mev (70 percent), 0.44 Mev (16 percent),
and 1.3 Mev (14 percent)—-averaged for the first
four shots from H + 0.3 to H + 13 days
Gamma spectra were taken of the fallout samples
(WT-935), Scripps Institution of Oceanography;.T. R.
Folsom, Project Officer.
The objective was to obtain fallout data in freeocean areas, as a result of the fallout phenomena observed following Shot 1. Operational and technical
details were hastily contrived so that they could be
put into effect for the latter phases of Castle. Participation was concentrated on Shots 5 and G, and both
water-sampling and submerged-radiation-meter
techniques were used. Isointensity contours were
plotted as though the fallout had been received by a
fixed plane at mean sea level. Dose rates at H + 1
or H + 12 hours were calculated at 3 feet above the
fixed plane. These contours indicated that for Shot 5
total doses of 250 r or more could have been accu-
mulated throughout an area of about 5,000 mi’; for
as a function of time for Shots 2, 3, and 4.
the smaller yield of Shot 6, the hazardous area was
smaller.
Project 2.6b ‘“Radiochemical Analysis of Fallout”
(WT-918), Chemical and Radiological Laboratories,
Army Chemical Center; R. C. Tompkins, Project
Officer.
The objectives were to determine (1) the variations |
in chemical and radiochemical composition of solid
110
The two survey techniques gave similar results.
The direct gamma-radiation meter was well! suited
for rapid surveys and depth-of~penetration measure-
ments, while the water-sampling technique provided
specimens for more-complete gamma-spectrum and
other physical and radiochemical studies. It was