UNCLASSIFIED
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The surface material swept up into the fireball was converted to liquid
calcium oxide drops by decarbonation and melting of the coral sand grains.
The iron in the fireball collected on the surfaces of these calcium oxide
drops either by direct condensation from the vapor state or by the impaction
of small iron oxide drops. These small iron oxide drops were formed either
by direct condensation from the vapor state or by the melting and oxidation
of the steel tower.
The iron reacted in the oxidizing atmosphere with the calcium oxide to
form the dicalcium ferrite. In most cases a residual core of wnaltered calcium oxide was left. The fission products condensed with the iron, thereby
making the iron-rich areas of the particles radioactive. After cooling, the
calcium oxide in the central area was carbonated and hydrated by the carbon
dioxide and water vapor in the air.
During this process there was a consider-
able expansion which cracked the particles and formed fissures and veins
which filled with the calcium compounds diffusing from the interior.
Particles of the second type, consisting almost wholly of iron oxide,
were probably formed by the oxidation of small liquid iron drops formed by
the melting but incomplete vaporization of the steel tower.
The iron drops
would be readily oxidized in the heated air, and the condensing materials,
iron as well as the radioactive elements, would be dissolved and distributed
throughout the liquid drop.
There also is the possibility that the tower was completely vaporized
and that the iron oxide particles were formed by direct condensation of the
iron from the vapor state. However, Stewart! has made an analysis of the
growth of particles by a process of condensation and coagulation from the
fireball of a tower shot in which his assumed conditions were much the same
as those occurring at the shot studied here.
He concluded that the modal
diameter of the iron oxide particles would be only 0.1 p.
From his expres-
sion for the particle size distribution resulting from the condensationcoagulation process it can be inferred that it would be highly improbable
that the particles could attain a diameter of a few hundred microns in the
few seconds available for growth.
The third type of fallout particle described above was formed by coral
sand grains entering the fireball at a comparatively late time and collecting
on their surfaces the small, black, radioactive spheres.
These spheres were
too small to analyze but they were presumably fcrmed by direct condensation
of the vaporized material in the fireball.
The ccral sand grains were usually
heated sufficiently to decarbonate them (800 to 900° C) but not sufficiently
to melt the resulting oxide (25709 C).
‘hey were subsequently hydrated to
calcium hydroxide by water vapor and a thin outer layer of calcium carbonate
was formed by the carbon dioxide in the atmosphere.
In some cases the sand
grains were not heated sufficiently to decarbonate them and they still
retained the structure and composition of the original coral.
UNCLASSIFIED