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Russian Geiger-Mueller Detector

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Sulaiman

Wed Sept 20 2006, 09:09PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I just bought a Geiger-Mueller detector cheap (GBP 10.50 incl. p&p) off eBay

It's a Russian model DRSB-01 I and would like to share some information;

The GM tube is CBM20, Ne-Br2-Ar, 78 impulses per micro-Roentgen.
Easily measures background radiation (with external counter/timer)

The thing that surprised me is the Americium241 in smoke detectors.
I'd read that 241Am is an alpha source and GM tubes are insensitive to alpha
so I had quite a surprise when the GM started 'clicking' when brought near
the OUTSIDE of a working smoke alarm.
I took a 241Am source out of another smoke alarm (OK in UK - Illegal in US)
and it easily penetrated a thin steel sheet!
A bit of 'googling' later and I now realise that 241Am also is a GAMMA source!

With a half-life of 432 years, I'm wondering if using nuclear processing waste
for domestic purposes is a good idea?

Anyone got any interresting experiments for me to try?

Bjørn

Thu Sept 21 2006, 01:05AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

I scraped some material from inside a energy saving flurecent light and covered the Americium and when my eyes had adapted to the dark I could see it glowing in the corner of my eye. It also made a 74HCT14 chip oscillate because it ionised the air.

I also tried if it affected the trigger voltage of a NE-2H bulb and there were no measurable effect. I have tried different methods for generating a very small current to make a microcontroller tick over once in a while with no luck.

You should connect the detector and a GPS to a microcontroller and carry them with you for a week and plot the results on a map.

Dr. Shark

Thu Sept 21 2006, 11:35AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I think every alpha or beta source also produces some gamma radiation. After spitting out a particle, the nucleus is left in an excited state, so it sends out a gamma photon as it decays to the ground state. I suppose it is rather low energy radiation for Am, so it does not count as a gamma source

Wilson

Wed Nov 08 2006, 10:27AM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

I thought GM counters worked on the gas inside the tube being ionised, and the free electrons that are liberated being attracted to a positive anode in the centre, producing a small current that can be detected. If such is the case, then alpha radiation, being the most strongly ionising of the 3 *should* produce the most clicks...

Sulaiman

Wed Nov 08 2006, 01:26PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

True - IF the alpha particles could penetrate the (thin) metal wall of the G-M tube
which they can't. even a sheet of paper will block alpha particles/rays.

(although the energy of alpha particles may be high
they are relatively huge -alpha particles/helium nucleii)

I now have a ZnS scintilation screen so that I can "see" the alpha particles
with my home made spinthariscope.
Amazing how many particles per second come off a smoke alarm Americium source.

'googling' revealed that Americium is mainly an alpha source
but also a gamma source due to the decay chain.

Steve Conner

Wed Nov 08 2006, 02:47PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Wilson: The thing you described isn't a G-M counter. It's called a proportional counter or something. G-Ms use a higher voltage such that any particle that enters it triggers an avalanche of ionisation, breaks the tube down completely, and produces one count, no matter what kind of particle it is.

Tesladownunder

Wed Nov 08 2006, 04:34PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

For sources and experiments, I have a lot on my site. My GM tube has a mica window and is sensitive to alpha emission. I get 80.000 counts/min from an Americium source. This is alpha radiation as it is largely blocked by paper.
Other sources include Uranuim marbles. I also have Yellowcake (processed Uranium ore), Thorium in welding rods, Potassium salts, Mineral sands, Tritium in a glow ring, and Radium from antique watch faces.
Later, I hope to use it as an x-ray detector as it can go down to 7keV.

Peter

1163003648 10 FT16261 Geigeramericiumalpha80180

Sulaiman

Thu Nov 09 2006, 07:58PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I bought my G-M deterctor on a whim,
a thin mica window would have been much better
- but mine was cheap and interresting and I'm almost finished 'playing' with radioactivity for now.
I did however find radioactive (gamma) uranium glass in one of the local charity (second-hand/used) shops.

Surprisingly a bearded (Muslim) guy going around the shops with a geiger counter (with added earpiece) caused no concern at all.

ragnar

Thu Nov 09 2006, 10:18PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Sulaiman wrote ...

...Surprisingly a bearded (Muslim) guy going around the shops with a geiger counter (with added earpiece) caused no concern at all...

LOL, that's because we know you're a mature well-intentioned, non-nutter, probably didn't have that 'twinkle in the eye' and tried not to grin like a serial killer (as I tend to do) whenever you found something radioactive. ^^

Probably also says something good about the shop-owners, too.

The world needs more exemplary people like you. Or at least to open their eyes and recognise them.
http://www.coxandforkum.com/archives/000775.html

Avalanche

Thu Nov 09 2006, 10:45PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Many years ago I had an analogue clock kit, which came with a small pot of glow in the dark paint for the numbers on the face. There was probably about 25ml of the paint. Come to think of it, i'm quite surprised they supplied that much radioactive stuff, there was loads left.

Judging by the amount of junk in this house, i'd probably need a geiger counter to find it

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