Table 1.
Concentrations of §08mAg in Samples from
Eniwetok Atolls
Date of
Bikini and
Concentration
Location
Samples
collection
of 1°8mAg
Eniwetok
Atoll
Bikini
Atoll
Bikini
Atoll
Bikini
Spiny lobster (20) *
(hepatopancreas)
Spiny lobster (3)
(hepatopancreas)
Spiny lobster (9)
(hepatopancreas)
Crater sediment
August 1964
0.20 + 0.04 +
(d.p.m./g
dry wt)
Atoll
June 1969
1.1403
June 1970
0.75 40.15
July 1969
0.09 + 0.05
* No. in parentheses signifies the number of individuals comprising
the composite sample analysed. Species: Panulirus sp.
{ Errors represent the 67°% confidence level of the count rate
measurements.
The sediment (Table 1) was taken from the site of a large
thermonuclear detonation in 1954 (Bravo Crater), the crater of
which is exposed to both lagoon and sea water and which is
therefore a source of 1°*™Ag for the biota of the area (1)°"Ag
having largely decayed between 1954 and 1969). Thermonuclear tests at other sites in the atoll have also produced silver
radionuclides. The last test at Bikini was in 1958, yet we have
measured a '!°™Ag concentration of 5.2+0.06 d.p.m./g of soil
on Eninman Islet at the atoll and thus the amount of 1°8™Ag
present in the Pacific Ocean and elsewhere as a result of pre-1959
testing may be significant.
The second observation about the initial production activity
ratio of 11°™Ag/'°8™Ag in ref. 1 may be conservative in its
estimate of '°®™Ag production. As we have said, the initial
activity ratio of '!°™Ag/'°8m™Ag was assumed to be due only
to thermal neutron activation of stable silver. There are other
production mechanisms for these two radionuclides, the most
notable being (n,2n) reactions on stable sifver (1°8™Ag) and (n,p)
reactions on stable cadmium ('°8™-11°™Ag), The cadmium react-
ion is probably not important because the quantity of stable cadmium in nuclear devices would probably be kept to a minimum
on account of the large thermal neutron cross-sections. The
excitation functions for (n,p) reactions at atomic weights
between 100-110 and neutron energies between 10-20 MeV
(ref. 4) are small (1-100 mijlibarns) by contrast with the excitation functions for (n.2n) reactions at atomic weights > 100
and similar neutron energies, which are significantly higher
(> 1 barn).
cm
nee a