Study of the Rateof Physical Decay of Radiation in the
Biological Samples
The Rongelap samples are now unique among our Marshall
Islands collections since they were taken from an area -Rongelap Atoll -- in which the radioactivity resulted primar-
ily from a single time source -- the March 1, 1954 Bikini experiment; whereas the activity at Eniwetok and Bikini derived
from several experiments over a number of years.
Rongelap decay data were studied with three primary objec-
tives:
(1) to evaluate suitability of the decay correction fac-
tor based on soil by a comparison of biological and other mater~
tela,
(2) to aid in extrapolating into past or future time beyond
the period of the present survey, and (3) to compare decay rates
with decline rates.
Eighty-four samples of fish,
invertebrates, algae, land
plants, plankton, birds, and soil were counted an average of
11.5 (range, 2-73) times for various intervals during the perfod from 38 to 500 days after the Bikini test of March 1, 1954.
When log of count is plotted on the ordinate against log
of time after March 1, 1954, on the sbscissa (here called a
log-log plot), a more nearly straight line ts usually obtained
than whenthe abscissa is arithmetic (semi-log plot).
‘A mixture
of fisston products is supposed (Coryell and Sugarman)” to give
@ straight line by log-log plot with = slope of about -1.25 for
the period of time involved in thie study.
The decey of a single
(nr
* Coryell, C. D. and Sugarman, N., Radiochemical Studies: The
Fission Products, Book 1, p. 456, McGraw-Hill, 1951