DISCUSSION
Decline and decay compared
The foregoing results show the decline trends for a pertod
un to two years following detonations.
It {is tnmror’ant to be
able to predict the future course of declines more than tvo
years after the cessation of testing.
Since prediction of
radioactive decay of samples is possible on the basis of their
radilolsotop!c content as determined by radiochemistry,
spectron-
etry, etc., an understanding of the relationship between decline
and decay will help in extrapolating future declines.
Decline rate was clerrly steeper than decay rate for the
alga Halimeda, the coral Acropora, and for most samples of sea
water, plankton, and sea cucumbers.
Decline and decay vere
nearly equal for island soil, most beach sand samples, clan,
snail, and reef fish. The data were insuffictent for comparison of the green leaves of land plants, crabs, terns, and rats.
The slight indication of a steeper average decay than decline
for beach sand at Leroy, if valid, might be caused by a continuing influx of activity from some reservoir, such as the
crater, after the collection of the decay samples.
In @ few cases decay rates were steeper than decline,
probably because of uncertainty as to the decline rate: island
soil at Janet, beach sand at Belle and Vera,
sea water on the
ocean side of Belle.
The steeper decays of plankton at the
Mike crater and of be&ch sand at Leroy appear to have more validity.
However, all of these cases could occur by chance in
the process of making as many comparisons 4s are represented
in this paper.
Clearly the balance is on the side of steeper
declines than decays.
Decays tended to become more nearly level as time progressed for Acropora, Crenobita, tern, and rat, while for snail
the decays became steeper instead of less steep, and for plankton,
Halimeda, clams,
and sea cucumbers the decays continued as
essentially straight lines in log-log plot.
The declines showing the mos* pronounced tendency toward
leveling near the end of the obsecvition npertod were Halimeda
at Belle, Janet, and Henry; leaves of land plants, Acropora,
and Coenobitea carapace at Belle; asd ses cucumber gut at Henry.
In some of these c&ses at least,
vagary of sampling.
tne noted trend is simuly a
That the tendency towerd terminal leveling is not tne
general rule among the decline data is siggestet by the poattion
an