RE: dose calculations

[glen.vickers@exeloncorp.com]

Tom,

You'll need to be careful in this area.  As an exampe, a NaI detector will
give the dose to that detector, but that detector does not necessarily have
the same energy absorption characterisitics as that of tissue.  This is why
you hear of "tissue equivalent" detectors.  A plastic scintillator could be
tissue equivalent, but the cross section for photoelectric interactions is
so low that it would never be good for spectroscopy.  You'd essentially
probably pick up a compton photon spectrum as the peak and never see the
photopeak.  I've collected some spectrums with Ba-133, Cs-137, and Co-60 on
a waste survey table and the FWHM is "broad" to say the least and would not
work for spectroscopy.  A NaI detector has better photoelectric cross
section than plastic , but still has poor energy resolution such that the
peak search/fit algorithms would have difficulty determining true mean
energies for the photopeaks.  This would be especially difficult in a power
plant environment where many of the energies are close together.  I would
think a semiconductor detector would offer the best resolution and the
detector could be covered with tissue-equivalent plastic.  The size of such
a detector would still probably be pretty small and therefore have a low
efficiency.  In high dose rate areas you might need to be able to handle sum
peaks and escape peaks, but the probability of these reactions should go
down as the active volume of the detector goes down.  Tell us more about
your instrument.

Once you solve all of the tissue equivalent issues, then you'd probably use
the reference that Ted supplied: 

ANSI/ANS-6.1.1-1977 (N666) Neutron and Gamma-Ray Flux-to-Dose-Rate Factors

This is the reference we used in college, but I'm not sure if there is a
better reference out there these days.  I haven't doodled with dose response
functions in quite a while...

Glen Vickers
glen.vickers@exeloncorp.com



> -----Original Message-----
> From:	Pxrfcorp [SMTP:tom@XRFCorp.com]
> Sent:	Friday, January 12, 2001 9:59 AM
> To:	Multiple recipients of list
> Subject:	dose calculations
> 
> Hi Radsafers,
> 
>     I am working on a hand held gamma/beta spectrometer.   Since it has
> a microprocessor and DSP it should be able to be programmed to do energy
> compensated dose measurements.  Does anyone know where I might find
> references on this topic,  equations, etc. that would be of use.
> 
> Thanks
> 
> Tom Hazlett
> 
> ************************************************************************
> The RADSAFE Frequently Asked Questions list, archives and subscription
> information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html


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