The average concentration of 239-2405, in A Site over all three
strata is 11.0 + 8.07 pCi/g (X + S.E.) which is close to the 21 + 6.6
(1975, Table 16),
pCi/g reported in Gilbert et al.
for the <5,000 cpm
The plutoregion in Area 11, of which A Site is a part (Fig. 1).
nium levels in A Site are low compared with those at B, C, and D
Sites in Area 11 (Table 16, Gilbert et aZ.,
vegetation mean to soil mean for
1).
1975).
The ratio of
239-2405, in A Site is 0.095 (Table
If one considers only the 14 paired soil, vegetation Pu concen-
trations, the ratio of vegetation mean to soil mean is 0.064 + 0.096,
which is similar to that reported in Gilbert et al.
for Area 1l.
(1975, Table 17)
The paired vegetation-soil data for 2354 and 2381 for
all strata combined are plotted in Figs.
3 and 4.
The estimated
linear correlation between soil and vegetation is 0.93 for 2354 but
only 0.35 for 2387
The higher correlation for 2354 could be related
to the preponderance of this isotope in the device, whereas the 2385
present is primarily natural uranium.
Three models have been fit to these data in Figs. 3 and 4.
1.
oy, = 8x, +e;
A
n
n
, where 8, = on Yi! de Ky
2.
yy = Box, + ey
, where 8, = Pa (y,/x,)/n
3.
y, = By + 8x, +e;
,
A
n
and
the usual linear regression model (see Snedecor and Cochran, 1967, p.
167,
for discussions on Models 1 and 2).
inappropriate for both 2354 and 2381
It is clear that Model 2 is
that Model 1 is considerably
better, but that Model 3 is the best of the three for 2351, it too
being inadequate for 238y.
The poor fits using the commonly used
ratio estimates 8, and 85 suggest that calculation of such ratios
without first plotting the data and checking for adequate fits can
give misleading results.
Gilbert et al.
(1975) report similar poor
fits using By and B5 for 239-2405, concentrations in adjacent soil
and vegetation samples at the other safety-shot sites.
Model 3 was
also fit to the logs of the soil and vegetation pairs, but the
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