18
USE OF A PORTABLE WHOLE-BODY COUNTER
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GAMMA RAY SPECTRA OF PLASTIC MAN
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Fic. 5. y-Spectrum of the calibration phantom
containing Cs!87, Zn®5 and K*in the approxi-
mate range found in Marshallese subjects. The
broken lines indicate the results of spectral
stripping of the higher energy photopeaks.
the subjects. The summary ofthe averagelevels
of Csl87, Zn, K49 and Co® determined in 1961
for both the exposed and the non-exposed
Marshallese, according to age and sex, is
presented in Table 2. The frequency distribution of values in various groupsis illustrated in
Fig. 7,
Cs87, The mean value for all the groups for
the body burden of Cs? was 13.7 nc/kg body
weight. Although the mean levels of the
exposed are slightly higher than those of the
unexposed groups, they do not differ significantly from each other. Variation in any
groupis large, as can be seen from Fig. 7 and in
the value of standard error. As expressed here
in terms of body weight, Cs!*? body burdensin
the groups over 16 years of age and in children
under 16 years do notdiffer significantly. The
mean levels of Cs’ in females tend to be
somewhatlower than the levels in males, but the
difference does not appearsignificant (Fig. 7).
Zn®, Zn® body burdens per kg body weight
appear to be somewhat lower in the younger
population group but, again, the differences are
notstatistically significant. Females also tend to
have values lower than those found in the corresponding male group (Fig. 7). No significant
difference between the Zn® concentrations in
the exposed and unexposed groups could be determined. The per cent variation within each
group was approximately the same as that
observed for the Cs!*? levels.
K49_ The mean K concentrations for the
younger groups wereconsistently higher than
those for the corresponding adult group. The
male adult group averaged 2.13 g/kg body
weight, while the female adult group averaged
1.63 g/kg.
Co®®, Analyses of the residual spectra
obtained after subtraction of the three above-
mentioned photopeaks revealed the presence of
the two photopeaks of Co®°, The levels of Co®
were quite low (mean = 0.148 nc/kg), but were
nevertheless readily detectible. No significant
differences between the Co® levels in the
exposed and unexposed groups, or on the basis
of age or sex, were observed.
Total residual y-actiity. The total residual
gammaactivity level present after subtraction of
the four above-mentioned spectra are also
shown in Table 1. The activity in cpm/kg has
no absolute significance, but is of value in
indicating first that there is some activity left,
and, secondly, the nature ofits distribution by
groups. Members of the adult group have
considerably higher levels of residual activity
per unit body weight than do membersof the
juvenile group. No significant differences were
observed, however, on the basis of sex, or
between the exposed and non-exposed groups.
DISCUSSION
It is interesting to note that no significant
differences in the body burdens of the four yemitting radioisotopes measured in the 1961
whole-body spectrographic study were observed
between the groups of Marshallese exposed to
fallout in the 1954 accident and those living in
the same environment as the exposed persons
for the last four years. The original contamination of the exposed population of these yemitters has already been eliminated, and what