Radioecology
rates were of limited usefulness.
‘
as
mixed fission pro—
7 aha Mooret ical decay curve for
the composition of
are cts could not be used because
not that of mixed
the ouclides in the samples was
estimate of
Mission products. Probably the best
that is deterdecay can be made from a decay curve there
will be
for each sample, but even then
e of uncertainty because of the need to
is not necesthat
late from a decay curve
7
a log-log
eerilylinear on either a semi-log or
Zplot.
A limitation on the interpretation of the
Folankton data resulted from the use of whole samples including many species of organisms rather
Ethan of samples which were sorted by species. The
Zeomposttion of plankton catches varied a good deal
from catch to catch and the uptake of specific nuclides by various species of plankton organisms
a
could be expected to differ markedly; therefore,
#the variation in radioactivity of whole plankton
fsamples may reflect species differences only.
However,
separation of these plankton catches into
species is entirely impractical because, in addition
to the great effort required, the quantity obtained of each species would provide only a minute
sample.
Accuracy of the estimate of the rate of transport of Hardtack fallout by the North Equatorial
Current was limited by lack of information as to
the exact time and place of entry of the fallout
into the ocean. There may be an error up to 50
days in estimating time and one to two hundred miles
in estimating place of entry.
Also, it was assumed
{that the fallout was transported in a direct line
_ between the two points of reference, but Miyake et
jal. (1955) have shown that there is considerable
jdeviation in the flow of the North Equatorial Cursrent near Bikini and Eniwetok.
It is obvious that
} the percentage error in calculating rate of trans: port becomes less as time and distance increase.
i
4
i
é-
CONCLUSIONS
The following conclusions are based upon data
; presented in Appendix Tables A and C and Figures 2
* and g.
(1)
It appears reasonable to assume that sig-
respectively,
204 and 356 micromicrocuries per gram of wet weight.
(6) Gross beta counts of some Guam and Palau
samples prior to the arrival of Hardtack fallout
indicated the presence of radionuclides from prior
test series. Values were higher at Guam than at
Palau.
Two estimates of the rate of westerly advance
of Hardtack fallout were made:
one, the rate from
Eniwetok to Guam;
the other, from Eniwetok to
Palau. The estimates were based on the assumption
that the fallout occurred at Eniwetok on June 15
(mid-point of test series), traveled in a straight
line to Guam and to Palau and arrived at Guam on
November 15, 1960 (mid-point between the October,
1958, and January, 1959, collections) and at Palau
on Febuary 15, 1959 (mid-point between the January
and April, 1959, collections). The calculated
rates were 8.0 and 8.1 nautical miles per day, respectively. The closeness of the values is fortuitous but they are in reasonable agreement with
previous estimates of the rate of transport by the
North-Equatorial Current of fallout from other
test series. From data published by Miyake et al.
(1955), Harley (1956), Seymour et al. (1957), and
Lowman (1960) the calculated rate for periods
from one month to one year ranged from seven to ten
nautical miles per day.
In Table 1 the amounts of specific gamma-emitting nuclides as determined by gamma spectrometry
are tabulated.
Samples were selected for type,
area of collection, and high gross beta count.
In
addition to naturally occurring potassium-40, the
radionuclides present,
in order of abundance, were
cobalt-57, cobalt-60, manganese-54, cerium-144,
zinc-65, zirconium-95, and silver-110m.
The great-
It is to be noted that silver-1l0m was reported
as cesium-137 and manganese-54 at the time this paper
was presented at the Symposium. The nuclides had
for the Gulf of Siam,
(3)
from 3.5 to 6.6.
The counts of gross beta activity
j differed greatly for the three collecting areas.
€ counts of Guam samples were considerably
® higher than those from Palau, which in turn were
Very much higher than the counts of the Gulf
= er Siam samples. The levels of radioactivity in
7
e Gulf of Siam samples were approximately back} @roun
d and
did
colle
Mot
ction
. not chan ge significantly with date
(4) The arrival at Guam of Hardtack fallout
rearsported by the North Equatorial Current occurarrivelwa October, 1958, and January, 1959. The
fates pt Palau was approximately three months
;
ney and for spider snail liver were,
« from Hardtack.,
} ranged fro 3.9 to 6.1 micromicrocuries per gram
of wet weight; for Palau, from 3.5 to 5.6; and
Se
(5) The samples with the highest gross beta
counts were clam kidney (Tridacna sp.) and spider
snail liver (Lambis lambis). The relatively low
values for liver samples of Palau spider snails
were an anomaly. The highest values for clam kid-
est value was 2,300 micromicrocuries of cobalt-57
per gram of wet weight of clam kidney (Tridacna).
(2)
One type of sample in which the presence
; Of Hardtack fallout was not evident was fish mus1 cle, for which the counts remained at essentially
background level for all collections regardless of
| date or area of collection.
For Guam the values
wm
the species composition of the plankton catches.
_ nificant increases in gross beta counts of some
' marine biological samples were a valid criterion of
the arrival of water-transported, local fallout
g
activity were considerably lower than at Guam.
Variation in the counts of the weekly plankton samples from Palau partially masks the upward trend
of the counts during the first part of 1959. This
variation is believed to be due to differences in
ac sha
tween January and April, 1959, but was not
rply indicated because the levels of radio-
been identified by gamma spectrometry and the two
principal gamma peaks for silver-110m, 0.67 Mev
(million electron volts) and 0.89 Mev, were mistaken for the 0.66 Mev gamma peak of cesiun-137
and the 0.84 Mev gamma peak of manganese-54.
Further investigations by Palumbo and other co~
workers in our Laboratory suggested the presence
of silver-110m, which was verified by chemical
separation of silver from the sample and by gamma
spectrometry of the separated component. The
identification of silver-110m is of special inter-
est because it is a fallout nuclide which has not
been reported previously, and so far it has been
detected only in the liver of the spiny lobster.
At the time that silver-110m was identified in the
sample of spiny lobster, collected at Guam in
November 1959, Palumbo also identified as silver-
110m an unknown nuclide in spiny lobster liver
collected at Eniwetok in March 1961.
Gamma-emitting nuclides other than those listed
in Table 1 may have been present in the samples but
‘were not identified because their radioactivity was
below the level of detectability, or their photopeak
DOL ARCH
Vis