-~6The Nectar test (May 14, 1954) was used as the date of
origin except where otherwise indicated, but earlier shots also
contributed radioactivity to the samples studied. Especially
the Bikini (March 1, 1954) shot contributed greatly to some of
the samples.
Residual long-lived products from earlier detona-
tions prior to 1954 rendered the curves less steep than they
would have been as a result of the 1954 series alone.
The trends of activity as related to time are of two kinds,
the physical decay of individual samples, and the rate of change
in activity of a certain type of sample at a certain locality.
To distinguish it from physical decay,
referred to tn this report as decline.
the latter trend will be
Results are shown as graphs of the relationship of logar-
ithm of radioactivity to logarithm of time of collection after
detonation. The date of origin used may deviate somewhat from
detonation day or the true origin without markedly affecting
linearity of the plot over the period of study. The slope is
changed according to the date of origin selected, but if the
same origin is used for both decay and decline,
compared.
the two may be
Hunter and Ballou (1951) show on logarithmic plot the
theoretical decay of mixed slow-neutroninitiated fission products of U-235
over 4& period from 1 to 1000 days as a
slightly curving line with a predomi-
nantly
below)
downward curvature (concave
and a general slope varying
af
from -1.0 to -1.7, averaging -1.2 (Fig. 2).
In log-log graphs it will be con-
venient to speak of slopes or rates of
decline and decay as becoming more or
less steep with the passage of time, and
when the terms steepening or leveling are
Fig. 2
“
T
radioactivity observed in the present
study facilitates comparison with this
curve and within the study itself.
Grass Radsometively
A similar presentation of the trends of
a
Days ofiee ate-veviven Reeien af 0
applied to the trends, the log-log
Fig. 2. Mixed fission
half life when plotted semiloga-
beta.
relationship is implied.
A single
rithmically gives a straight line,
while on the same plot a mixture of
half lives results in a line of
product decay, gross
(After Hunter
-and Ballou).
increasing steepness.
In the declines shown as straight lines on log-log plots
possible fluctuations of a cyclic nature attributable to season
or other variables are ignored.