7
mostly Jess than 1 micron in diameter, contained about 85% of the radioactivity in the fallout droplets from these types of detonations (Scheli, op.cit.);
*
saturated sodium chloride (sea salt) droplets in which these insoluble
solids were suspended contained the remaining 15% of the measured radioactivity.
The second type were detonations in shallow water or on land surfaces
(sites B,J,G,1,C,H, in Fig. 2) and were used for the three largest tests conducted at Bikini.
From explostons of this type, Adams et al. found that
condensation of the vaporized materials typically occurring as impurities into
and on the surfaces of the coral soils swept into the fireball, producing two
distinet types of fallout particles.
partially hydrated to Ca(QH)o.
One was spherical particles of Ca0
A surface coating of Ca(OH)o and/or CaC03 was
present due to the reaction of the particle with water vapor and atmospheric
CO2 during the fallout.
These particles were formed by high temperature
(>2570 C) vaporization of coral with subsequent condensation of the oxide as
a spherical particle which had lost {its normal porosity.
The radioactivity
was almost uniformly distributed throughout the particle.
The second char-
acteristic particle was angular, and consisted of Ca(OH)2 with a thin outer
coating of CaC03.
Some of these particles contained an unmelted coralline
sand fragment as a central core.
The bulk of the radioactivity was con-
teined {n the outer carbonate shell.
The angular shape of these particles,
the lack of incorporated radioactivity, and the presence of occasional un-
mocified sand grains led the authors to suggest that these particles were
formed from nonvolatilized coral which was heated enough to melt and de-
Certonate (800-900 C), while incorporating only an outer surface of condensing
ractonuclides,
Occasionally, 10-micron and smaller spherical particles
Produced by direct condensation of the refractory Fe and Ca vapors at early
times in the fireball were observed adhering to these parti
cles.