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The difference in the specific activity (pCi/g) of the fine-grained
debris collected at stations B-21 and B-20 can be explained by one or combinations of two processes.
One is a dilution in the concentration of radioactive
particles deposted at Station 8-71 by lower specific activity material arising
from biological activity or erosion of the reef.
Secondly, the difference in
the specific activity of the sediments at stations B-21 and B-20 could arise
via a physical or chemical fractionation of the radioactivity in, or from,
debris which is transported in suspension.
A physical fractionation could
arise by differences in the specific activity of different sized particles.
The specific activity of relatively larger sized particles deposited at
Station B-2], for instance, may be lower than that of small particles deposited
further downstream.
Chemical fractionation of radionuclides may be a function
of the length of time radioactive particles remain suspended.
Particles which
were deposited at Station B-21 may thus have lost a higher proportion of their
surface-associated radioactivity than those deposited at stations B-2 or B-20.
The relatively high specific activity of the sediments collected at stations
B-22 and B-24 would be consistent with deposition of the high specific activity
material fractionated--whether by physical, chemical or biological processes-from sediments suspended upstream.
Figure 20 is a photomicrograph of surface sediments from Station B-20,
adhering to scotch tape, at 20x magnification.
are about 200 p in diameter.
The largest particles observed
However, many of these particles are agglomerates
characteristic of dried sediments.
Figure 2] is a photomicrograph of Station
B-20 surface sediments dispersed in water (pH = 10) and magnified at 80x.
Nearly all of the particles observed in these samples are smaller than 50y in
diameter and a large number are smaller
than 10y in diameter. The very sma?)