cheap geiger counter?
Microwatt, Mon May 02 2011, 06:01AM

made from scintillator screen+ photodiode+ transistor+ lm311 comparator?

Re: cheap geiger counter?
tarakan2, Mon May 02 2011, 07:28AM

no way
you will need to stand in the middle of a reactor for the light diode to pick something up

you are not counting the number of particles but measuring the intensity of the light produced by a flow of particles

unless you are inside focusima or chernobyl sarcophagus, that aint gona be useful

Re: cheap geiger counter?
Proud Mary, Mon May 02 2011, 09:37AM

Microwatt wrote ...

made from scintillator screen+ photodiode+ transistor+ lm311 comparator?


This type of circuit is employed in many professional instruments using PIN photodiodes, both with and without a scintillator, but a few words of explanation:

At 10 keV detection efficiency approaches 100%, a figure which falls to about 1% at 150 keV.

There are two basic modes of operation:

A: DC Current Mode, where the current flowing through a PIN photodiode is proportional to the incident radiation.

B: Individual Photon Counting Pulse Mode - where the PIN photodiode is coupled into a charge integrating amplifier. Here we see a gamma photon strike on a PIN photodiode (top trace) with the resulting comparator output on the trace below:






Nowadays, specialised gamma ray detecting PIN photodiodes are available (at a breath-taking price!) from the likes of Centronic and Hamamatsu, BUT common glass lens type PIN photodiodes such as BPX65 were used in professional dosimeter designs until quite recently.*

For use below about 15 keV, the glass lens of BPX65 should be removed, so as not to block low energy photons.

PIN photodiodes have replaced GM tubes in many applications, and are used extensively in gamma ray spectrometers.

Don't underestimate the technical challenge of the charge integrating amplifier! The circuits look elementary, but bad layouts, poor component selection, and inadequate screening will catch the woolly-minded every time!


* See, for example, US Patent 5059801 assigned to the UK National Radiological Protection Board



Re: cheap geiger counter?
Inducktion, Mon May 02 2011, 12:46PM

Proud Mary wrote ...

Microwatt wrote ...

made from scintillator screen+ photodiode+ transistor+ lm311 comparator?


This type of circuit is employed in many professional instruments using PIN photodiodes, both with and without a scintillator, but a few words of explanation:

At 10 keV detection efficiency approaches 100%, a figure which falls to about 1% at 150 keV.

There are two basic modes of operation:

A: DC Current Mode, where the current flowing through a PIN photodiode is proportional to the incident radiation.

B: Individual Photon Counting Pulse Mode - where the PIN photodiode is coupled into a charge integrating amplifier. Here we see a gamma photon strike on a PIN photodiode (top trace) with the resulting comparator output on the trace below:






Nowadays, specialised gamma ray detecting PIN photodiodes are available (at a breath-taking price!) from the likes of Centronic and Hamamatsu, BUT common glass lens type PIN photodiodes such as BPX65 were used in professional dosimeter designs until quite recently.*

For use below about 15 keV, the glass lens of BPX65 should be removed, so as not to block low energy photons.

PIN photodiodes have replaced GM tubes in many applications, and are used extensively in gamma ray spectrometers.

Don't underestimate the technical challenge of the charge integrating amplifier! The circuits look elementary, but bad layouts, poor component selection, and inadequate screening will catch the woolly-minded every time!


* See, for example, US Patent 5059801 assigned to the UK National Radiological Protection Board





If pin diodes can be used for cheap Geiger counters,

Would something like that work as a cheaper replacement than the BPX65? How sensitive is it to other forms of radiation, if at all?




Re: cheap geiger counter?
Proud Mary, Mon May 02 2011, 01:10PM

Inducktion wrote ...

Proud Mary wrote ...

Microwatt wrote ...

made from scintillator screen+ photodiode+ transistor+ lm311 comparator?


This type of circuit is employed in many professional instruments using PIN photodiodes, both with and without a scintillator, but a few words of explanation:

At 10 keV detection efficiency approaches 100%, a figure which falls to about 1% at 150 keV.

There are two basic modes of operation:

A: DC Current Mode, where the current flowing through a PIN photodiode is proportional to the incident radiation.

B: Individual Photon Counting Pulse Mode - where the PIN photodiode is coupled into a charge integrating amplifier. Here we see a gamma photon strike on a PIN photodiode (top trace) with the resulting comparator output on the trace below:






Nowadays, specialised gamma ray detecting PIN photodiodes are available (at a breath-taking price!) from the likes of Centronic and Hamamatsu, BUT common glass lens type PIN photodiodes such as BPX65 were used in professional dosimeter designs until quite recently.*

For use below about 15 keV, the glass lens of BPX65 should be removed, so as not to block low energy photons.

PIN photodiodes have replaced GM tubes in many applications, and are used extensively in gamma ray spectrometers.

Don't underestimate the technical challenge of the charge integrating amplifier! The circuits look elementary, but bad layouts, poor component selection, and inadequate screening will catch the woolly-minded every time!


* See, for example, US Patent 5059801 assigned to the UK National Radiological Protection Board





If pin diodes can be used for cheap Geiger counters,

Would something like that work as a cheaper replacement than the BPX65? How sensitive is it to other forms of radiation, if at all?


I'm sure that a number of PIN photodiode types will work to some degree, but I wouldn't want to make guesses about the performance of parts with which I am not familiar. Small surface area to keep capacitance down to a bare minimum is essential for correct operation of the charge integrating preamplifier. BPX65 has a 1 mm.sq active area, and also has the advantage of metal can self-screening which becomes critical with ultra-high impedance electrometer inputs.

PIN photodiodes in pulse mode can be used for the direct detection of alpha particles.*


*See: Jpn. J. Appl. Phys. 47 (2008) pp. 1740-1741

Ultraviolet-Sensitive Windowless Silicon PIN Photodiodes for Alpha-Ray Spectrometry

Mitsuteru Mimura, Nobuyuki Hasebe, Shingo Kobayashi, Mitsuhiro Miyajima, Tadayoshi Doke, and Eido Shibamura

Energy resolution measurements of ultraviolet-sensitive windowless silicon p–i–n photodiodes were carried out with alpha rays. A resolution of 12.6 keV in full width at half maximum for 5.486 MeV was achieved. The ultraviolet-sensitive silicon p–i–n photodiodes were found to be suitable to alpha-ray spectrometry.



Re: cheap geiger counter?
Microwatt, Mon May 02 2011, 02:57PM

So why cannot a solar cell be used?

Re: cheap geiger counter?
Proud Mary, Mon May 02 2011, 03:12PM

Microwatt wrote ...

So why cannot a solar cell be used?



Solar cells can be used - and were used - as X-ray detectors in the Gy/hr regime (i.e. it would not be nearly sensitive enough to detect typical amateur sources such as mineral specimens of 100 μGy/hr at most for best pitchblende)

See below: Journal of Applied Physiology January 1963 vol. 18 no. 1 209





Note the meaty X-ray tube anode currents needed to bring the solar cell to life. Using the figures from the graph - 80kV, 500mA, 30 inches - the dose rate needed to produce 2V across the solar cell is a roasting 1100 Gy/hr.

Re: cheap geiger counter?
Microwatt, Mon May 02 2011, 03:59PM

but this can easily be overcome by biasing the solar cell a few hundred milivolts and using a comparator to detect events.

Re: cheap geiger counter?
Proud Mary, Mon May 02 2011, 04:32PM

Microwatt wrote ...

but this can easily be overcome by biasing the solar cell a few hundred milivolts and using a comparator to detect events.


Well if you say so, who am I to disagree?


Re: cheap geiger counter?
Microwatt, Mon May 02 2011, 05:24PM

I mean do you think it would be possible to set up a solar cell to detect alpha particles if you have bias on the junction.

Re: cheap geiger counter?
James, Mon May 02 2011, 05:32PM

You can get Russian GM tubes for ~$20 on ebay, so until those run out, why even bother trying to cook something up?

Re: cheap geiger counter?
Conundrum, Mon May 02 2011, 06:00PM

Or make your own using a vacuum pump, suitable tube, epoxied on mica window and some commercial argon for welding.
Total cost is probably less than a single end window tube as the vacuum needed is only 1% which is well within the requirements of even a single stage pump salvaged from a defunct air conditioner or even a car aircon system.

Also, any old CMOS camera with its glass removed will detect alphas as I rediscovered a few years back.

-A