Thinking of building myself a simple geiger counter.

[Refrigerator]

Hey.
The other day i was watching all these X-ray videos and all that and got interested in these geiger counters. I looked at the prices and don't feel like spending money right now ( tight budget ! ).
So i naturally looked up a way to make one but most of them used this high voltage tube, but some others used this simple " aluminum tube with a copper wire inside " sensor things inside, i thought i might try to make one, maybe test it by pointing it at my big old CRT TV to see if it works. 
Yet i don't know if those aluminum tube things really work, maybe any of you guys have seen/tried/heard of those kind of "sensors".
From what i know the "rays" are supposed to hit the tube and ionize some electrons (?) which then hit the copper wire that is inside and would display as a voltage across the outer aluminum tube and the copper wire inside.
My idea is to make a simple opamp circuit to sample the tiny voltage that came out of the tube and the output of the opamp would power a little " BJT with negative resistance " kind of oscillator which would make little " crackling " noises, through a small speaker indicating the "radiation".
But that's just me yapping about .
I'd like to hear something from people who are more experienced in this type stuff.
Of course some help would be appreciated.

[hamster_nz]

Have a look at using a PIN Diode as a (relatively insensitive but workable) sensor.

http://www.instructables.com/id/Pocket-Photodiode-Geiger-Counter/

[vindoline]

You're talking about an ionization chamber. Check out the info on Charles Wenzel's site: techlib.com

[kripton2035]

some schematics and infos about diy geiger counters.
here : http://kripton2035.free.fr/geiger-repositor.html

[Refrigerator]

Hmm, i think for now i'll just experiment with the simple ionization chamber, maybe order the photo diode for later experimentations.
The ionization chambers are rather instable when moving them around because some electrostatic charge builds up,  wonder if i can make two small ionization chambers close to each other, but one would have reversed charge on the can/inner wire to hopefully decrease some, if any of that electrostatic problem.

[penfold]

Ionisation chambers built how you describe do work quite well for a very basic measurement.  I wouldn't be sure that they would detect anything much in the x-ray end of the spectrum, at normal atmospheric conditions they will have a very low efficiency for gamma/xray but when it comes to alpha/beta they will detect very well.
I frequently work with ionisation chambers that are sensitive to high energy gamma and still, despite the best design optimisation, still only produce minute currents (10 pA down to 100 fA) for reasonably intense fields of gammas.

A Geiger tube is probably the way to go to detect every-day sources of radiation

[vindoline]

Agreed, a simple diy ion chamber is excellent for alpha radiation and very insensitive to gamma.

[Refrigerator]

I've found some STS-5 geiger tubes on ebay for about 15 bucks, i'll save up some cash for those later on.
Now i want to try with what i have.
Also if i made one with pin photodiode, could i connect them in parallel and make a small panel to increase the sensitivity ?

[bktemp]

I've found some STS-5 geiger tubes on ebay for about 15 bucks, i'll save up some cash for those later on.
Now i want to try with what i have.

For a working geiger counter tube you need a suitable mixture of gas, because it must be able to stop the ionization itself after each pulse.

Also if i made one with pin photodiode, could i connect them in parallel and make a small panel to increase the sensitivity ?

If you connect more photodiodes in parallel you increase the area. Therefore you will get more pulses. But this also increases their capacity and this decreases the amplitude of each pulse.

[penfold]

For a working geiger counter tube you need a suitable mixture of gas, because it must be able to stop the ionization itself after each pulse.

That isn't strictly true, the avalanche of ionization is stopped by means of a quench circuit, the mixture of gasses is select such that the ions quickly recombine so that when the full potential is applied to the tube again there aren't enough ions remaining to restart an avalanche.

You will get a reasonable result with a tin-can ionisation chamber, just be prepared to get a beta emitter (I used potassium salt before with reasonable success) but you have to watch out for any sources of ionisation disturbing your results.  And when you think you're getting a positive result by moving the source nearer and farther from the chamber, its probably just to your hand moving that gives most of the reading!

[denelec]

The March 1950 issue of Popular Science (available online on Google Books) has an article on how to build a very simple geiger counter.

http://books.google.ca/books?id=KS0DAAAAMBAJ&printsec=frontcover&dq=popular+science+1950&hl=fr&sa=X&ei=DtVoVNa4F8WdygSoqoGYCg&ved=0CEIQ6AEwBg#v=onepage&q&f=true

[croyleje]

mightyohm has some great info on making a geiger counter and kits i believe are still available there is also some great info on how the tubes work below is a link.

http://mightyohm.com/blog/products/geiger-counter/

jason