96
naturally occurring radionuclides was also used to help detail the origin
and accumulation processes of sediment and transuranic radionuclides with
depth in the sediment column, in selected samples.
The results of these
measurements are found in Table 15 (uranium), Table 16 (“"
226
Ra), and Appendix
III (219p9),
Station C-3 (Bravo Crater) Sediment Core.
The distribution of
238,
U,
226
Ra and
210
Po concentrations measured in the
Station C-3 core are also shovm in Figure 22.
All three radionuclides show
increased concentrations in the 0-10 cm region of the core, compared to their
concentration in lower sections.
Although the distribution profiles of these
three radionuclides are not as wel] detailed as the 24) Am or 155 Eu profiles
measured, the increase in the 226p 2105, and uranium concentrations in the
0-10 cm layers is not apparently different from the well-defined increase in
the
24)
Am and
155
Eu concentrations which were observed in detail.
Although
the absolute uranium concentrations measured in the 0-2, 6-8, 30-32 and 50-52
em'sections of the core varied by a factor of 4, the 234 238), ratios in each
section varied from 1.06 by less than 2% (< 1 S.D. propagated counting error).
These observations indicate that either: (1)
238), and 234), contamination
have been selectively added to sediments in the upper 8-10 cm of the core in
activity concentrations similar to those present in (on) the coral in lower
sections (whose radiological signatures differ in other respects), or (2)
the pulverized materia) in the upper 8-10 cm of the core is old sediment (of
about the same
apparent age as the sediments in deeper sections) which
naturally contains a higher uranium concentration, or (3) the 238) 2344
enrichment on the particles in the 8-10 cm section did not originate from
bomb materials, but was artificially concentrated on the particles; first by
a volatilization of the coral sediment in the fireball, and then condensation