In
Aa
3
DESCRIPTION OF THE FALLOUT PARTICLES
Three types of radioactive fallout particles were observed.
The most
abundant particles were spheroidal, dull black, cracked and veined with
white crystalline material and varied in size from about 1/2 to 1 mm in
Giameter. Examination of the thin sections of these particles revealed
that they had a diffuse, central core of what had originally been calcium
oxide but which had been subsequently converted to calcium carbonate and
calcium hydroxide.
a
1a
ce) ON
UNCLASSIFIED
ome eee eee ee ee
‘
r
7
F
Surrounding this central core was a thick zone of black,
opaque material which was identified as dicaleium ferrite (2 Ca0°Fep03).
The white material filling the veins in the particles, andsometimes o¢ecurring as surface coatings, was found to be mixtures of calcite and vaterite.
Calcite and vaterite are different crystal modifications of calcium carbonate
and differ from the crystal form of the calcium carbonate in the original
coral which is largely aragonite. The radioactivity in this type of particle
was always associated with the areas of dicalcium ferrite; the calcium com-
pounds in the core and veins were inactive (see Fig. 1).
The second most abumdant type of particle was spherical, black with a
glossy luster, magnetic, and about ue mm in diameter.
These particles were
found to consist of magnetite (Fe30)) and some hematite (Fe203).
The radio-
activity was distributed more or less homogeneously throughout the volumes
of the particles (see Fig. 2).
The third type of particle was found comparatively rarely. These particles fF
were white and irregular in shape, and had the appearance of coral sandgrains.
Examination of the thin sections showed that these particles were composed
E
either of unaltered coral or of calcium hydroxide with a thin outer coating
.
of calcium carbonate. Adhering to the surfaces of these particles were many
:
Fig.
cons
scopic. Radioautographs revealed that -these small black spheres were the
carriers of the radioactivity and that the large calcium carbonate or hydroxide
:
|
(gra
part
ORIGIN OF THE FALLOUT PARTICLES
i
The fallout particles of the first type described above were formed by
the interaction of the condensing material, which had been vaporized in the
fireball, with the surface material swept up into the cooling fireball by
atmospheric turbulence.
The vaporized material consisted predominantly of
iron derived from the steel tower and some calcium oxide derived from the
coral sand.
UNCLASSIFIED
8 paige men tamees oe
particles were inactive (see Fig. 3).
f£
penn
small, black spheres ranging in size from about 10 p in diameter to submicro-
ani