-23-
Thus, it seems desirable to report radioactivity of plankton on an
ash weight basis, even though other organisms and substances might
more desirably be considered on a wet weight basis.
Figure 8 shows the trend of radioactivity in the plankton samples
from Rongelap lagoon (from 1954 through 1958) related to time, using
a log-log plot of the beta activity on an ash weight basis as determined
with a methane-flow counter.
Data are from Tables 3 and 4.
The
dotted line showing a decline slope of -3.5 was fitted by inspection to
the minimal points near 300, 600 and 1500 days, points removed as far
as possible from the peaks caused by the Redwing and Hardtack series
of detonations.
The maximum level of the lagoon plankton a day or two after March
1, 1954 may be conjectured by extrapolating back one cycle on Figure 8.
It appears that maxima must have been at least 20, 000 uc/kg of ash.
Further reference to Figure 8 showsthat the original detonation,
Bravo, must have contributed 100 times as muchactivity as the Redwing
series, and Redwing 20 to 100 times as much as the Hardtack tests.
The decline picture is characteristic in its pattern.
Rises result from
the fallouts, followed by steep declines until the next fallout.
An
ex-
ception appears in the region of Kabelle Island in late 1954 and from
1956 to 1957.
Figure 9 shows, on log-log plot, the decay patterns of six samples
counted on more than three occasions.
Ordinal values on the vertical