DExUS

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.

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.

MAIN CIRCUIT

First of all we have to get rid of the A/D converter and power supply, that will leave us only with the detector unit.

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.
The 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 

Now perform these steps

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 🙂

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.

If you have some issues with the application feel free to contact me at my e-mail .

 

Before I leave few photos of my setup I have to mention few warnings.

“WARNING the software is only experimental, collected data might not correspond with reality”
“WARNING radioactive materials can be dangerous, please use only low and by law allowed amounts of radioactive materials”