Re: Re[2]: Ionization at 80 eV? (Yes)

["baumbaug@nosc.mil" <baumbaug@nosc.mil>]

        Jeff,

        I didn't see your e-mail address, so I'm answering you via radsafe
(sorry everyone),

        Your answer is, - It depends....

        I am "CERTAINLY" not an expert, but I'll try and answer your
question (very generally).

        In gas filled detectors, the proportional region  is from about 220
volts up to around 800-850 volts.  G.M. from around 850 - 950 volts
(wherever your tube starts discharging).  There is a lot of gray area here
due to a LOT of differences in equipment.

        In gas flow type proportional counters, your proportional region
starts around 800 volts for your alpha region - and your beta region (again
depending on your equipment) may go up to 2000 volts or more...

        Hope this helps,


        Joel Baumbaugh (email baumbaug@nosc.mil)
        NRaD


        Std. disclaimer - The opionis above are mine and mine only!  The
Federal Govt., the Navy and my bosses may not agree with the above information.


  
At 08:37 AM 5/19/97 -0500, you wrote:
>
>     I'm confused.  I was under the impression that the Geiger-Muller 
>     region was at a distinctly higher voltage than the Proportional 
>     region.  My DOE Fundamentals of Instrumentation book places the 
>     Proportional region of the gas ionization curve at between ~300 and 
>     ~800 volts and the Geieger-Muller region at ~1000 to ~1400 volts.  I'm 
>     guessing that these curves are gas dependant (the handbook is quiet on 
>     just what gas the curve is relevant to).
>     
>     A GM Tube at 900 volts and a proportional detector at 4000 volts 
>     doesn't make sense to me unless the ionization curve is gas dependant 
>     and differing gases are used in each.  Is this the case?
>     
>     This is of interest to me since my FacRep oral board is tomorrow and I 
>     may or may not have to talk about the mechanics of radiation 
>     detectors.  (Probably not, but better safe than sorry.)
>     
>     Jeff King
>     US DOE Facility Representative
>     Savannah River Operations Office
>     In-Tank Precipitation Facility
>     
>
>
>______________________________ Reply Separator
_________________________________
>Subject: Re: Ionization at 80 eV? (Yes)
>Author:  dale@radpro.uchicago.edu at Mailhub
>Date:    5/16/97 5:05 PM
>
>
>It is not so simple.  An 80 ev photon  or electron can easily ionize 
>something, but it is the electric field not so much the potential 
>that is important.
>     
>Think about it.  Gm tubes typically have 900 volts between the anode and 
>cathode.  Proportional detectors I have used needed up to 4000 volts. 
>Both of these need ionizing radiation to trigger an event.  The _field_ 
>is insufficient to ionize even though the potential is there.
>     
>Dale Boyce
>dale@radpro.uchicago.edu
>
>
Joel T. Baumbaugh (baumbaug@nosc.mil)
Naval Research and Development (NRaD)
San Diego, CA., U.S.A.