95
than was 23942405 and in the 8-10 cm section the ordering sequence was the
3ame aS at lagoon stations B-16, R-25 and B-22 to the west.
The constancy of the concentrations of all radionuclides measured to
depths of 10 cm (core B-27) and 16 cm (core B-15) shows that a considerable
penetration of radionuclides has occurred in these sediments which appear to
he normal lagoon deposits.
Assuming a negligible natural sedimentation rate,
the penetration of radionuclides into these sediments is significantly greater
than was observed by Held (these results are presented in section 3.4) in
Rongelap Atoll sediments.
However, these two sediment cores were the longest
obtained from any station in the atoll having unpulverized sediments, suggesting that these sediments may have been significantly less consolidated than
average.
This could explain both the length of the core and the radionuclide
concentration with depth.
§.3-4
Uranium, Polonium-210 and Radium-226
As noted previously, the radioisotope activity ratios
234) /
238
U and
226...
Ra/-~
,234
U existing in carbonate sediments reflect the degree of
disequilibrium between the incorporated parent and daughter radionuclides of
the uranium series.
On a time scale of ca. 10°-10° year, these ratios can pro-
vide information on the age of the denosits.
in concentrations above those maintained in
Similarly, 2105, which is present
situ by 2263 decay, permits sedi-
mentation rates to be determined over a time scale of about 150 years.
In Sections 5.1 and 5.2, the high °2°pas294 U
ratios measured in the most
contaminated, and pulverized, surface sediments collected, are interpreted as
Showing that these sediments are ancient deposits removed from the detonation
craters.
In Section 5.1-8, the areal distribution of relatively constant un-
supported 21054, concentrations is interpreted as evidence for the slow accumu-
lation of the 210 Pb by natural processes.
The distributions of these