Geiger Counter + Gamma spectrum analyzer under 10€

Hi guys,

there is an older article that I posted on my website few months ago that might interest you.
It's a fun project for weekend I'd say, and you can get some interesting results out of it.
Here is the article:


The title of the post says it all.
But it might be very hard to imagine to build such complicated instrument with budget under 10€ but it's possible, kind of.

MAIN CIRCUIT

I came across a circuit scheme that seemed easy to build but it was intended to be used with 8Bit A/D converter (original article).
This converter is used with parallel (LPT) port which can't be found on modern computers.
Also the 8Bit converter offers only poor resolution of 256 levels of energy and it is hard to calibrate.

The original cuircuit consists of 3 sections, Detector, Converter & power supply.
And I decided to make it alot more accurate and a lot more easy to build.



The circuit is very simple and consists only of parts which all together are under 10€ or if you probably have resistors and capacitors at home it will cost you about 2€ just for the TLC 272 and the BPW34 photo diode.

As detector of the gamma radiation is used a photo diode, the diode generates current once it's hit by photon, electron or gamma radiation.
But when hit by gamma or beta the voltage is so small that for us to be able to detect, it needs to be amplified and the impulse needs to be prolonged with low noise operating amp.

Due to that, one of the most important part is the shielding and the power supply.
Whole circuit has to be placed in shielded box, best from aluminum.
The detector circuit needs to use 9V battery as power supply to minimize noise.

Don't worry about the power drain, the circuit takes only 1,3mA and standard 9V battery (6F22) will last for ~13 days of uninterrupted operation.

For more sensitivity I recommend to use 3 or more photo diodes added in paralel as the detector, you will get very low amount of hits with just only one, but it will work fine.
Cover the diodes with some tape or plastic to block all light.
You have to add "BETA" shield as I did with a piece of grounded aluminum  (see photos below), which probably won't stop all the BETA but to perform the spectroscopy you will need only the GAMMA radiation to hit your sensor. (in this case photo diode array).
Be also sure to use nice shielded cable to connect the detector to your Microphone input on your computer sound card.
You can plug in also your headphones, however the "click" sound will be so faint that you must listen closely to hear them.
Thats were the computer comes in.

Component list:

• IC - TLC 272
• D1 - BPW 34
• R1 - 470ohm
• R2 - 470k
• R3 - 270k
• R4 - 4,7M
• R5 - 330k
• R6 - 1k
• R7 - 10k
• C1 - 47µF/16V
• C2 - 22pF
• C3 - 470nF
• C4 - 150pF
• C5 - 100nF
• C6 - 100nF

SOFTWARE

I had made a very simple application that will count the CPM (Counts per minute), and perform a very inaccurate but functional spectroscopy of the energy received.

"PIN Diode Gamma Spectrum Analyzer" can be downloaded here : DOWNLOAD

How to setup the software :

1) Power up the detector without any radioactive material inside
2) Plug it in to your sound card "Microphone in" , be sure to set the default  microphone in windows settings.
Do not apply any microphone boost setting, that will add only noise and inaccurate readings.
3) Start the "PINDGSA" application.
4) Move with the Threshold scroll bar until you will get clear "no" input signal as shown on the picture below.
5) Put in the sample you want to measure.
6) Enjoy

Video instructions:


The application will show CPM right away, however to start the spectrograph you have to press START button.
To get the complete spectrum histogram you have to wait several minutes or hours, depending on the amount of radiation of your sample.
More time means more accuracy.
Application auto saves every measurement in "<install dir>\measurement" directory.
You can load the histogram back anytime and even continue measurement if it needs to be stopped for some reason.


You can find the original article with more pictures here : http://www.dexus5.com/system3/geiger-counter-gamma-spectrum-analyzer-under-10e/

No problem adding the support, but what purpose will it serve ?
The detector is so weak that in order to detect something there has to be almost direct contact with radioactive material.
There is like 1 hit of background radiation per several minutes.

This looks similar in concept to the phone/tablet apps where the camera is used in the same way. The lens must be completely blocked, and after accounting for noise somehow, any remaining sensor output is assumed to be Beta or Gamma. I've tried one Android app called "Radiation Alarm" that gives a count, and I've seen another paid app that has calibration settings for various phones and looks well designed. I don't know if any of these measure and store amplitude differences like this circuit seems to do.

I know about the existence of those apps, they work only with good sensors and strong radiation source.
And they can't do any spectroscopy (at least the ones I had seen).

In a way, photographic sensor is just a large quantity of photo diodes which are small.
And this circuit uses one (or as I recommend 3) photo diode with large surface where the emited particle can hit.

The paid app is RadioactivityCounter by Rolf-Dieter Klein