RE: GM Calibration

["Pollan, Paul B." <PBPOLLAN@southernco.com>]

What about Solid State GM Detectors?

> -----Original Message-----
> From:	Heinmiller, Bruce [SMTP:heinmillerb@aecl.ca]
> Sent:	Tuesday, December 07, 1999 12:44 PM
> To:	Multiple recipients of list
> Subject:	RE: GM Calibration
> 
> Although G-M tubes give no energy information on the electrons entering
> the
> gas, for a given photon fluence incident on the tube wall, there is very
> definitely energy "information", insofar as the number of electrons
> capable
> of reaching the gas is higher for higher-energy Compton electrons
> generated
> from higher-energy photon interactions in the tube wall.  Energy
> compensation for lower energies notwithstanding, I believe that's how G-M
> tubes are able to measure exposure (or exposure rate) over a wide
> photon-energy range.  SCPE of the incident field is not relevant provided
> the tube wall is thick enough to re-establish SCPE in a volume element in
> the tube wall near the gas, and in that sense it is an issue.  While the
> response (ignoring dead-time) is purely determined by the number of
> ionizing
> electrons entering the gas, I submit that this number has no meaning with
> regard to exposure unless SCPE exists in the tube wall near the gas.  It
> is
> the number of electrons entering the gas under SCPE conditions in the wall
> near the gas that I refer to as the SCPE complement of electrons.
> 
> Bruce Heinmiller CHP
> heinmillerb@aecl.ca
> 
> > ----------
> > From: 	Lieskovsky, Miro[SMTP:MLieskovsky@nbpower.com]
> > Reply To: 	radsafe@romulus.ehs.uiuc.edu
> > Sent: 	Tuesday, December 07, 1999 10:46 AM
> > To: 	Multiple recipients of list
> > Subject: 	RE: GM Calibration
> > 
> > Bruce,
> > I agree with your posts that the overresponse is due to the secondary
> > electrons from air reaching the GM's sensitive volume.  
> > 
> > I think that the SCPE is not an issue with the GM tubes because there is
> > no
> > information on imparted energy in the count / pulse.  Or existence of
> SCPE
> > simply does not matter for the GM tubes.
> >   
> > The primary electrons (when measuring betas) or the secondary electrons
> > (predominantly from the tube wall when measuring photons) are important.
> > As
> > you point out the GM tube detects (almost) every single electron that
> > enters
> > its sensitive volume.  The resulting pulse is of the same size
> regardless
> > of
> > the  imparted energy from the electron and that is why no information on
> > the
> > amount of absorbed energy can be extracted.
> > 
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