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My own geiger counter engineering

Posted: Thu Sep 12, 2019 3:59 pm
by Xymox
If this forum is the wrong place for this post, just delete the thread. This forum seems to be the best place to discuss geiger counter engineering so I am going to post here with some observations and questions if its OK.

I am a electronic engineer with tons of analog engineering experience. As a fun project I decided to play with making a background radiation / cosmic ray shower observatory. I decided to make this 100% from my own engineering. Its been VERY interesting and challenging.

Ive been thru 3 wholly different approaches. The first 2 were based on a digital chip that counted up CPM.. This digital approach has all sorts of disadvantages. While its alluring to look at a geiger tube pulse as a digital signal best processed in the digital world, its not the best way IMHO.

I have now done a completely analog approach to this. The pulses are dumped via Schottky diodes into 3 RC integrators providing 3 different averaging outputs. 1 sec, 1 min, 2 hours. The 1 sec integrator provides instantaneous up and a decay down. So the 1 sec output shows ray showers VERY clearly because they come with bursts very close together in time.

The tube and supply for it was serious engineering. All the designs I have seen are simple and not ideal. These tubes are ultra high impedance AND high voltage. On top of that for best performance the power supply needs to be very low noise and well regulated. The high impedance of the circuit of 5-10M makes it very susceptible to all sorts of noise. The resistors are also sources of noise at these high values and high voltages. I ended up using metal foil resistors and really high quality multi layer ceramic caps. It also turned out that thermal drift mattered as well. Attention to 1/f noise was important as well.

I did not expect all this attention to engineering was going to be required for a device that produces fixed voltage pulses. I discovered that even small amounts of noise raised self counts. Good regulation produced a more stable number of pulses per minute.

I ended up using a Dataq 14 bit A/D datalogger hooked to the 3 integrators.

Im using 3 x SI-22G tubes.

This is about 2 days of logging.
So I have some questions.

I have purchased a proportional counter tube and I was wondering if anyone had any experience using this as a cosmic ray observatory ?

I like the idea of a scintillation counter so I could also measure energy but photo multiplier tubes are a whole different set of engineering, is it worth it ?

Is the SI-22G the best for background / cosmic ray observing ?

Re: My own geiger counter engineering

Posted: Thu Sep 12, 2019 5:28 pm
by Xymox
I also looking at Spectra of the background.. Im seeing small, but consistant, deviations from the expected 1/f spectrum.

I can't find any information on the spectrum of background..