Bo
=
d|r
n
n
LX Yy/K
i=l
on the grounds of a better linear regression fit through the origin
for the latter.
It is felt, however,
that the general topic of ratio
estimation for plutonium and other transuranics needs further consideration, particularly in view of the skewed nature of these environmental
data.
Some thought needs to be directed toward optimum methods of
estimating ratios when both numerator and denominator are, say,
lognormally distributed.
For example, if both are lognormal,
then
the individual ratios Y,/Xy are also lognormally distributed, which
Suggests a method efficient for estimating lognormal means might be
considered (Aitchison and Brown, 1969, p. 44).
A related problem is
the bias that is known to be present to some extent in
By and By
when the 241 Am data are subject to error (Snedecor and Cochran, 1967,
p.
164).
235
The new data from A site, Area 11, will permit the estimation of
to 238)
and 239-2405, to 241 an ratios in soil and vegetation.
U
The
2334 to 238y ratio will decrease with increasing distance from GZ
235
238
since the device was made up predominately of
U.
The
Pu to
239-240
Pu ratios can also be computed for the soil samples analyzed
by Los Alamos Scientific Laboratory
(LASL).
Some additional
plutonium and americium data from TTR and Area 11 sites will also
permit the update of estimated ratios given in Gilbert, et al.
(1975).
Some new analyses of the ratio data may also be useful.
For example,
there has been no attempt to explain the variability observed in
vegetation to soil plutonium ratios.
It would prove informative to
investigate whether high Pu concentrations in vegetation tend to be
associated with low Pu concentrations in soil.
This is suggested by
the Stratum 3 Double Track vegetation and soil data
1975, Fig. 32).
(Gilbert et al.,
If so, this could be a reflection of the particulate
nature of Pu in the soil samples versus the less variable
(more
homogenous) vegetation solutions from which aliquots for analysis are
drawn.
108