Interferences with Pb212 Analyses?

["Leo M. Lowe" <llowe@senes.on.ca>]

We had some NORM samples (slightly elevated uranium) analyzed for thorium.
The thorium  (less than 10 ppm) and Ac-228 (< 0.1 Bq/g by gamma spec)
results were not inconsistent with typical background soil levels, but the
short-lived Pb-212 (by gamma spec) showed values more than an order of
magnitude higher than expected based on the thorium levels.  Samples blanks
and a number of sample standards showed no unusual Pb-212.

The lab is at a loss to explain the elevated Pb-212 levels shown by the
gamma spec.  Has anyone had any similar experience or have a possible
explanation i.e. potential interfering gammas?  There don't appear to be
any escape peaks that would interfere.  You may contact me directly with
your suggestions.

Thank you.

Leo M. Lowe, Ph.D.
llowe@senes.on.ca

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