Re: Detector for finding contamination depth profile

[JMiller929@aol.com]

[Subj:	Detector for finding contamination depth profile]
[Date:	96-05-15 17:26:05 EDT]
[From:	xug2@rpi.edu (George Xu)]

[Hi, Radsafers,]

[Is there any detector system (or calculational algorithms) which let you]
[determine how deep the contamination (gamma and/or beta) is in, say,]
[concrete or other materials?  As you know, this is useful during]
[decommissioning and waste disposal.  Thanks!]

[George Xu]
[Rensselaer Polytechnic Institute]
E-mail: xug2@rpi.edu]REPLY:
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If you are fortunate enough to be measuring nuclides with multiple gamma
energies [e.g. Cs-134, Eu-152, preferably with the gammas at widely separated
energies], then the ratio of the gammas is a function of depth distribution.
 When you use a Ge detector to measure the gammas, they are quite easy to
separate from the natural radioactivity in concrete.  

Therefore, just create several efficiency calibration curves, each with a
different depth distribution profile, find the depth distribution profile
that best matches your unknown, based upon the ratio of activities of each
peak.  

While you can't totally prove that your assumed profile is correct, you can
easily prove which ones aren't correct, and eliminate those.  

Of course, making up these multiple depth profile efficiency curves can be
quite expensive in terms of time, radioactive materials, and waste disposal
costs.  We have developed various mathematical models which we use for this,
and have found them generally to be more accurate than the fabrication of
these complex sources.  One of these models is MCNP, which is commonly
available, and VERY difficult to figure out, but quite accurate.  We are also
creating a software product for sale in a few months.  When this product is
used with one of our special Ge detectors, it will allow the user to create
these various efficiency depth profile curves very quickly [minutes].  

I hope this is a suitable answer to your question.  

If you know Dr Ivor Preiss, please say hello. 

Frazier Bronson
Canberra,  Meriden CT
203-639-2345
fbronson@canberra.com