of the 1954 series at Bikini Atoll.
The levels of radioactivity of the algae immediately following the
test averaged 2, 500 uc/kg of wet tissue but declined rapidly, thus the
level from previous experiments (1.9 wc/kg) was reached in about
170 days.
At the conclusion of the study in April 1956, the average
level was 0. 10 wc/kg of wet tissue.
The trend for the period was one
of general decline of radioactivity, although there was some deviation
from this pattern.
B.
Rate of Decline of Radioactivity in the Sea Water
The amounts of radioactivity in the sea water collected in ‘ne same
area as the algae are given in Table 2.
In recording the results of the
radioactivity in the water, the data are reported in d/m/m1) instead of
uc/kg because of the very low levels found.
Onthe first day after the
test, the radioactivity in the water averaged 2,200 d/m/ml but it declined rapidly, so that on the last collection dates it was indistinguishable
from the background level.
A logarithmic plot of the decline in radioac-
tivity is shown in Figure 3, and it can be seen that the rate is
approxi-
mately the same as that for the algae, even though the levels in the
algae were approximately one thousand times greater.
From May 15, 1954 to May 19, 1954,
the ratio of radioactivity in
the algae to that in the water increased from 2, 500 to 14, 000, which indi-
cates that the algae were concentrating radioactive material even though