Internal Behavior of Europium

["Carbaugh, Eugene H" <gene.carbaugh@pnl.gov>]

The drop off you witnessed in europium content would be reasonable for a
predominantly ingestion intake form of relatively insoluble (e.g., class
Y) material which just passed through the GI tract.

While ICRP-30 suggests all forms of europium should be considered class
W, I'm not at all sure I agree.

We have had some experience at Hanford with Eu-154/155 created from
activation of samarium oxide marbles used in the (now retired) N-Reactor
as an emergency control system.  Quite a few years back (1970s - no
later than early 1980s) we had a few relatively minor exposures which
appeared to result in fairly tenacious lung-burdens, much more
indicative of class Y than class W behavior.  And no, we weren't seeing
bone (rib, sternum, vertebrae) activity and mistaking it for lung.  

Your experience is a good argument for collecting fecal samples even for
the situations where its easy to detect by in vivo.  Even one early
fecal sample would probably have given you a good handle on how much
might have been skin versus internal contamination.  However, the issues
of worker convenience and cost do come into play here.  In vivo
detection for Eu can be pretty good and give you the sensitivity you
need for reasonable dose assessments for compliance.  The difficulty
comes with what you are now trying to do - extend the "reasonable dose
assessment" to a technical understanding of the behavior of the
material.  For that you really need bioassay sufficient to do a good
material balance and the means fecal samples as well as in vivo.  Urine
samples would be fun, too.  

I'd be happy to talk with you more if you like.

Gene Carbaugh
Internal Dosimetry
Pacific Northwest National Laboratory

(509)376-6632
gene.carbaugh@pnl.gov