Natural abundance of Plutonium -Reply

[FRAMEP@ORAU.GOV]

G'day

The numbers I've seen are similar to those of Russ. The key thing is
that the Pu-239 levels (the only naturally occurring isotope of
plutonium) are tied to the U-238 levels. This is because the Pu-239
is produced by the reaction:

 U-238 + n   ->   U-239   ->  Np-239   ->  Pu-239

The neutrons are cosmogenic or come from  spontaneous fission or
alpha n reactions in the ground. 

The ratio of Pu-239 to U-238 atoms/mass seems to range from 1E-11 to
E-13. This is from a paper quoted by Eisenbud in his book Natural
Radioactivity. I've also got an old AEC report that says Levine and
Seaborg in 1951 (the report doesn't identify the exact reference)
found 7 parts Pu-239 in 1E12 parts Belgian Congo ore that has an
astounding 45% uranium content and 1 part Pu-239 in 1E14 parts of
lower grade ore with a 0.25% uranium content.

Of course us folk in the northern hemisphere have plenty of Pu-238 in
our soil/sediment/vegetation because of above ground weapons testing
in the good old days.

Best wishes

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov