Re: alpha/beta ratios for radionuclide identification

[Emil <kerremba@pilot.msu.edu>]

Teresa,
I have played with that idea in mono-nuclide cituation.
We did Ra-226 remediation project, wrote site-history paper for EPA to
prove that there was not and could not be any other staff beside Ra-226
and its progeny.
I did a some alpha/beta correlation for purpose of using beta
measurements and avoiding numeric alpha measuremnts in characterization
survey and may be using it later in the final release survey. There was,
of course, a alpha/beta correlation and relatively strong. But there was
two problems: 
 1) The same sample conditions.  Alpha absorbtion/shielding when there
dust was present, humidity level and geometry was different form flat
were given different alpha/beta ratios.
I would watch for the amount of dust and humidity in your case.
  
 2) measurements reproductivity.  Detector's alpha/beta efficiencies is
different with different gas pressure, we used gas proportional floor
monitor system for both alpha and beta measurements. 
If you use scintillation probe the second problem.
Stationery gas proportional counter you should not have either of these
problems.
But I would still wacth for the humidity level. It depends on how often
you will do counter calibration. And periodic cross check with other
methods would be a bad idea. 

So ideally you need to know the prior exact radionuclide contents, one
or other way, and have very reproductive-result(stable efficiency)
detectors. In our case, we had some problems with obtaning the same
efficiency/poor chi-square system test results in the survey process. 
Remember if you have  errors(deviations) in original measurements you
will get increased error(deviation) in their ratio.. 

Any way, in the end of the story: a more restrict alpha limit then beta
limit for Ra-226 did not allowed us to cut on alpha surveys. But for the
characterization survey purpose alpha/beta correlation/ratio could be
used if we have not failed to satisfy those two reqirements.   
I hope it may help.
Emil.

kerremba@pilot.msu.edu

Teresa G Hefley wrote:
> 
> I am in the process of counting various contaminated paper smears,
> spiked paper smears, NIST traceable sources, spiked glass fiber filters,
> and contaminated cellulose nitrate filters with a Tennelec LB5100 gas
> flow proportional counter.  The nuclides of concern are u-238, th-232
> and pu-239.  I am attempting to show that the differences in the
> alpha/beta ratio for each nuclide can determine the identity of the nuclide
> without using alpha spectrometry.  Does anyone have any experience
> using this method of nuclide identification?  I would like to know what
> results you have observed and what type of samples were used in the
> testing.  I would appreciate any comments on this matter.
> 
> Teresa Hefley, RPT
> Pantex Plant
> Amarillo TX
> thefley@pantex.com
> 
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