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Re: Homemade Geiger Counter

> Date:          Tue, 27 Jul 2004 11:48:22 -0400
> From:          "Robert Bruninga" <bruninga@usna.edu>
> To:            <amsat-bb@AMSAT.Org>, <aprssig@lists.tapr.org>
> Subject:       [amsat-bb] Homemade Geiger Counter

> As we approach armagedon, I thought it might
> be nice to have a Geiger counter.  
> Which, if I recall is just an ionization chamber,
> a voltge charge and an audio amp.  Since Radio
> Shack does not have GeigerMueller tubes, do I
> remember correctly that you could even use
> a flourescent bulb for the ionization chamber?
> Just thought it would be nice to have something
> to detect high energy particles around the house
> or on a satellite, or feeding alerts onto APRS?
> (hence asking on both sigs)..
> Bob

Dear Bob,

Nuts & Volts Magazine (the successor to Poptronics) had a 
construction artical for a GeigerMueller counter not too long ago.  I 
built several of them back in the 60's as highschool projects.  
Basically all they are is a low current HV supply across the tube.  
You tap the pulse off a resistor to ground in the P.S. circuit with a 
capacitor.  Then amplify the pulse or as I did, use it to charge 
another cap in a integrator circuit to drive a meter.  

I had a tuning meter out of WWII tank radio that had a Radium dial.  
It was HOT and made a great demo, lots of clicks!  One counter that I 
built used a very simple HV power supply.  I used two transistor code 
practice oscillator driving a reversed audio transformer to get 
100VAC.  A five stage voltage multiplyer got me up to 500 volts DC 
for the little GM tube I had.  Simple and it worked.  I suppose you 
could use a 555 as the driver now.

As for the neon bulb circuit one respondant refers to:

That brought back a lot of memories.  Mostly of me sitting in a dark 
hamshack in 1961 playing with NE-2's.  I discovered that you could 
use a pot to set the voltage across the bulb right below the 
ionization point.  Then when you turned a light bulb on, the photons 
would add just enough energy to the neon to kick them into ionization 
lighting the bulb.  I used this primitive and not too sensitive photo 
cell to operate a relay.  The drawback is once the NE-2 fired, it 
would stay ionized even if the voltage was reduced below the point 
where you could get it to trigger reliably.  In other words, it was 
sort of a latching circuit.  I also discovered I could trigger the 
NE-2 with my Radium dial meter.  Neat physics experiment!

NE-2's and their bayonet based big brother the NE-51H are still fun 
to play with.  

--73-- David WA0AUQ
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