RE: Dose from U-235 daughters

["Clement, Christopher" <clementc@aecl.ca>]

Although we don't measure for Pa-231 or Ac-227 directly, we do routinely
measure U-235 specific activity directly by HPGE gamma spectroscopy in
our more active soil samples.  It has several gamma decay energies which
can be used.  Be aware, however, that the strongest line at 186 keV (54%
intensity) is interfered with by a line of the same (almost) energy from
Ra-226 in the U-238 series.  We also measure Th-227 using the 236 keV
peak (11.2% intensity).  Both Pa-231 and Ac-227 are between U-235 and
Th-227 in the actinium series, so with these two results you should be
able to get a reasonable handle on the Pa-231 and Ac-227 specific
activities, even if the series in not in equilibrium.  In fact, even if
all the Th-227 were removed, it would be back in complete equilibrium
with Ac-227 in about 3-4 months (half life of Th-227 is 18.7d).

As for the dose contribution from U-235 and progeny, check out "Impact
of the U-235 series on doses from intakes of natural uranium and decay
progeny", a Note in Health Physics October 1997 by Leo Lowe.

------------------------------------------------------------
Christopher H. Clement
Scientific Specialist / Radiation Protection Program Manager
Low-Level Radioactive Waste Management Office
Atomic Energy of Canada Limited
clementc@aecl.ca



>----------
>From: 	David.Cowell@wssrap.com[SMTP:David.Cowell@wssrap.com]
>Sent: 	November 25, 1997 9:59 AM
>To: 	Multiple recipients of list
>Subject: 	Dose from U-235 daughters
>
>     Dear Radsafers - 
>     
>     Pa-231 and Ac-227 are two of the U-235 daughters which have high dose 
>     conversion factors (mrem/uCi).  They could be in the raffinate pits on 
>     our site at concentrations high enough to be a dose concern, but we 
>     have little info on this.  We are wondering if other sites similar to 
>     ours are accounting for these in their dose assessments, if they've 
>     even analyzed for these nuclides, and if they have, what analytical 
>     methods were used.  A few years ago we tried to get labs to analyze 
>     for these and were told at that time there no standard analytical 
>     methods for them.
>     
>     Please feel free to respond to me personally or to radsafe.
>     
>     Thanks,
>     David Cowell
>     
>     e-mail:  David.Cowell@WSSRAP.com
>