Simple Geiger counter

The circuit diagram above shows a simple Geiger counter. I designed it actually for a robot which will seek for the highest radiation exposure in a room, but many other applications are possible (for example Hardware random number generator). Beside the GM tube only standard components are used. The PCB mount transformer T1 is a 230V/6V version, operated in the opposite way as usual. The HV can be adjusted with the potentiometer R5 between approx. 300 and 1000V, therefore the circuit covers many different GM tube types. Check out the data sheet of the GM tube for the operating voltage and adjust the voltage before connecting the GM tube! Measuring point is between the cathode of diode D5 and 0V. Take care that your multimeter has a measurement range of min. 1000 V DC! Please also note, that the protective resistor R10 must be as near as possible on the anode of the GM tube. The capacitors C4 to C8 must be suitable for 630V AC. Keep also the creepage distances in mind.

Commonly available radioactive sources for experiments, tests and calibration can be found here.

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When I built this circuit, I had voltage spikes on the high voltage line whenever the 555 timer would transition high or low. These voltage spikes were large enough to prevent my geiger tube (an LND 712) from functioning. The output is 500V most of the time, but when the 555 transitions to low, it generates a voltage spike of 730V, and when the 555 transitions to high, it generates a drop in voltage down to about 300V. While the spikes are very short in duration, they are long enough to prevent the tube from working. I believe these spikes are the result of putting a square wave through the transformer instead of a sine wave.

How did you overcome these spikes?

Steve

I plan to give this a test build, be great if you could answer some questions for me:

What transformer(T1) would you recommend?

Can the 5V input be driven by battery pack?

what voltage would you recommend for C11 100mf?

Thanks

Hi,

PCB mount transformer 230V/6V with 1VA.

Circuit can be driven by a battery pack (4.5V or 4.8V)

C11 should have 16V or higher.

No need for Geiger tubes - there are also other radiation sensors.

Well, at least in theory. A solar cell or photodiode actually is a radiation sensor although for different wavelength. However, there are rumors that you can detect gamma radiation using such a device. I even remember a DIY article in a German electronics magazine (Funlschau) in the seventies or eighties. They poroposed to use several stacked solar cells with a voltage in blocking polarity. As soon as an energized photon hits them they will genreate an current implulse. When looking for solid states radiation detectors several months ago I found descriptions of a few PIN-diodes made exactly for this. However, no supplier, not even complete datasheets. There must be small solid state sensors. I don't believe that Geiger tubes are used in medical X-ray devices. Geiger tubes are nice, but expensive and not very stable or vibration-proof.

There are many ways to detect radiation. Depends one the application, which parts you want to use, your experience etc. One of my ideas was to put a cloud chamber with a camera on the robot. Through image recognition you can even determinate the corpuscle angle of entry. Just be creative and build some working hardware :)

Btw, here is a simple γ-photon radiation detector, using a PIN photo diode: http://www.maxim-ic.com/app-notes/index.mvp/id/2236

Thank you all!!

Fernando

Fernando,

Joined to tell you that the CL-3BG tubes are disappointing - not vary sensitive. Background count is 1-2 / min.

I also just completed a Geiger project and put links to tubes on my blog - http://brohogan.blogspot.com/

I'd suggest the SSBM-20 - background count ~ 35 / min.

Hi Fernando,

Should be both ok. Really cheap. I hope the tubes are not damaged.

Hi,

I've just registered. Excellent site. Will be around.

I'm going to make this detector! Just a question or two.

Where to get the GM tube?

At e-bay they are selling relly cheap russian ones from 10 to 30 \$ a piece. What do you think ?

http://cgi.ebay.com/Russian-GEIGER-TUBES-COUNTER-CI-3BG-NEW-BEST-CHOICE_W0QQitemZ180482132127QQcmdZViewItemQQptZBI_Security_Fire_Protection?hash=item2a0592c89f