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Old 09-11-2010, 10:30 AM   #1
barry wilkins
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Default Geiger counters

Bit of an odd ball question .
I Know roughly how a Geiger Muller tube works .
But does does anybody know how you can actually test a GM counter works ?
If I had a very old luminous watch the Radium would be detectable by the counter and it would click and show somes counts per second .
But luminous dials do not use Radium anymore .
So what can you use to see if it works ?

thanks

Barry Wilkins
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Old 09-11-2010, 10:45 AM   #2
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Default Re: Geiger counters

They use a calibrated source [known counts] to check it.
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Old 09-11-2010, 06:16 PM   #3
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Default Re: Geiger counters

Most of your ionization-type smoke detectors have a very small amount of Americium in the sensor assembly. The problem is most newer smoke detectors are impossible to open without destroying them.

Here is the link to details about the Americium: http://www.webelements.com/americium/
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Old 09-12-2010, 12:48 AM   #4
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Default Re: Geiger counters

I thought that was a beta emitter? Won't most geiger counters on ebay only detect gamma?
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Old 09-12-2010, 06:26 PM   #5
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Default Re: Geiger counters

Quote:
Originally Posted by pentium View Post
I thought that was a beta emitter? Won't most geiger counters on ebay only detect gamma?
there is some gamma off of that as well, just not enough to do you any real harm. anything glow-in-the-dark puts some off as well.
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Old 09-12-2010, 06:27 PM   #6
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Default Re: Geiger counters

Quote:
Originally Posted by pentium View Post
I thought that was a beta emitter? Won't most geiger counters on ebay only detect gamma?
there is some gamma off of that as well, just not enough to do you any real harm. anything glow-in-the-dark puts some off as well.

in chemistry 2 years back, one of our alpha sources fell out of the plastic disc. they teacher found it using a Geiger counter.
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Old 09-12-2010, 11:07 PM   #7
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Default Re: Geiger counters

Different meters have different capabilities.
Depends mostly on the type of probe.
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Old 09-13-2010, 06:26 AM   #8
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Default Re: Geiger counters

Quote:
Originally Posted by barry wilkins View Post
Bit of an odd ball question .
I Know roughly how a Geiger Muller tube works .
But does does anybody know how you can actually test a GM counter works ?
If I had a very old luminous watch the Radium would be detectable by the counter and it would click and show somes counts per second .
But luminous dials do not use Radium anymore .
So what can you use to see if it works ?

thanks

Barry Wilkins
It's very easy. The geiger counter I used had a cap covering the end of the probe. Zero the meter with the cap in place. Remove the cap. The needle should deflect upward one or two units on the most sensitive scale due to background radiation.

Or you can order a sample of pitchblende.

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Old 09-13-2010, 07:12 AM   #9
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Default Re: Geiger counters

If all you want to do is see the needle move then any of those suggestions may work.

If you want a number that actually means something then none of them will work.

The calibration frequency on 'good ones' generally varies between monthly and daily depending on what kind of meter it is.
The cal frequency for the 'accident' [or 'bomb'] emergency response type meters is 1 year but that type isn't all that accurate or sensitive [compared to 'good ones'] even when newly cal'ed.

The 'signal strength' these meters are designed to detect and measure is SO TINY that even small 'aging changes' in compont values in the meter will throw the reading way off.

Not the kind of meter you calibrate every few years and expect the numbers to mean anything.

~
"Background" is defined as <50 cps.
- That isn't because that is what background actually is, it is because below 50 cps the detector can't detect anything anyway.
Any reading below 50 cps isn't a reading at all, it's just the electronics in the meter 'wandering around' because the detector isn't sending anything. - Static.
[That applies to detectors a human can carry, not lab equipment.]
.

I was just outside an open reactor compartment doing some paper work.
There was a 'a good one' [type] sitting on the table 'on' at the Control Point.
[Control Point is where you check you didn't get crapped up while working in the compartment before you leave.]
Suddenly the meter goes from static background, alarms, and pegs the meter at 50,000 cps.
I shit! - That's what happens when a core cooling pipe ruptures!
Then it dropped to static for like 3 seconds, then it did it again and stayed at 50,000 cps.
I called out the casualty response team.
...
Turns out some moron contractor was tig welding inside the compartment and he ran his %#@&!~ cables right next to the meter.
.
That contractor is lucky I never found out exactly who did it.
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Last edited by PCBONEZ; 09-13-2010 at 07:21 AM..
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