"Large volume" gamma calibration sources

["Chris Clement" <clement@vaxxine.com>]

Frazier (and other interested Radsafers):

Our office needed some moderately sized, homogenous, soil-like sources for
calibration of a gamma radiation detection system that we developed to
measure radium in soil moving along a conveyor in real time.  We used this
system successfully for a cleanup project in 1995, and have kept the
sources for future use.

We started with a well homogenized volume of "play sand" (we tested it for
radioactive homogeneity by taking several aliquots for HPGE analysis). 
After dividing the sand into five and measuring the mass of each part, we
"spiked" four with known masses of CANMET certified ground ore and sediment
standards.  We then homogenized the four "large volume" standards (not a
simple task!), and tested for homogeneity, obtaining excellent agreement
between HPGE analysis of the aliquots from each large volume standard and
the predicted specific activities.

Each of the five "large volume" standards (four spiked plus one background)
are about 90 kg.  Not quite as big as you want for some of your geometries
but might be of some use, particularly since you can "pour" them into any
geometry container you want.  I don't have the full set of results in front
of me, but we spiked one with potassium to 3.35%, two with uranium (and its
progeny in equilibrium) to 19 and  38 ppm, and one with thorium (and its
progeny in equilibrium) to 33 ppm.  The fifth was not spiked, and I don't
recall the exact activities but I believe that the potassium was about 1%,
the uranium was about 2 ppm and the thorium was about 5 ppm.  Sorry, but I
don't have the uncertainties conveniently available right now either.

If you are interested, I can forward to you our full set of analyses (K, U
and Th on all five standards, plus a brief report on the homogeneity
testing results).

Chris Clement
Scientific Specialist
Low-Level Radioactive Waste Management Office
Atomic Energy of Canada Limited
clementc@aecl.ca
clement@vaxxine.com

----------
> From: fbronson@canberra.com
> To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject: Calibration Sources Wanted
> Date: July 9, 1997 9:05 AM
> 
> Hello RadSafers
> 
> We have developed a new instrument for field quantitative gamma
spectroscopy.
> It is called ISOCS, for InSitu Object Counting System.  It is
fundamentally a
> portable shielded/collimated Ge gamma spectroscopy system.  But one of
it's new
> features is a Mathematical Efficiency Calibration Software.  This allows
the
> user to develop energy-efficiency curves for a wide range of sample
sizes,
> locations, and energies, without radioactive sources.  The software is
designed
> to work for very small samples and very very large ones [e.g. large ISO
> containers, B-25 boxes, 55 gallon drums, 10000 gallon tanks, pipes,
> well-logging, ... ];  basically any defined object from 50 keV to 7000
keV, and
> any location within a 100 meter diameter sphere around the detector. 
> 
> With claims like that, our customers are asking for proof that it really
> works.  That is the purpose of this query.  Do any of you know the
existence of
> large well characterized and documented multiple energy gamma calibration
> sources?  Desired are B-25 boxes, ISO containers, pipe sources, large
flat
> surfaces, large and thick sources simulating soil contamination,
calibrated
> well-logging holes, large tanks filled with calibration sources, etc.   
The
> ones we have found so far at some well-respected government facilities
don't
> have much of pedigree; while they are probably OK, they aren't very
useful
> as reference sources. 
> 
> We have already gathered about 60 such comparisons from sources used here
to
> characterize and calibrate our waste assay products, and from some
concrete 
> calibration pads in Germany, and from many MCNP computations.  But we can
use
> more.  In general, we find the software agrees quite well with the MCNP
> computations and with "normal-sized" radioactive sources, but for large
> radioactive sources sometimes not as well.  After analysis, most of these
> "problems" have been due to the calibration source not being quite as
well
> known as originally thought.  Making good quality large sized radioactive
> sources is not an easy tasks.  We think that the calibration software is
> probably more accurate.
> 
> So, if any of you have sources, or contacts that might know of good
quality
> large sized multi-energy gamma calibration sources that we can visit with
our
> instrument, and borrow a few photons that are otherwise going to waste,
please
> let me know.
> 
> Also, if anyone wants information about the ISOCS instrument, or the
> mathematical calibration software, send me a reply.
> 
> thanks for reading this far.
> 
> Frazier Bronson CHP
> Canberra
> Meriden CT USA