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Simple, low-cost X-ray/gamma-ray detector based on PIN photodiode
Luke Weston, 2012

Released as Open Hardware as per the CERN Open Hardware License:

A silicon PIN diode (in this case an inexpensive off-the-shelf device designed for infrared optoelectronics), accompanied with appropriate electronics, can detect charged particle and energetic photon (X-ray or gamma-ray) impacts on the diode, allowing for basic qualitative ionising radiation counting (for educational use, for example) with very simple, low-cost electronics.

This removes the traditional need for expensive, difficult to obtain and fragile Geiger-Muller tubes or scintillation detectors, and the need for their associated high-voltage power supplies, for ionising-radiation detection or experimentation in a low-budget educational or hobbyist context.

For this device to operate correctly, the PIN photodiode must be in the dark, with all ambient visible and infrared light excluded from the photodiode. Since the sensitive JFET input stage is also quite sensitive to electromagnetic interference, an opaque metal box is probably the best bet for optical and electromagnetic shielding. The metal box should be connected to the DC ground.

A thin "window" made from a layer or two of black electrical tape covering a hole in the metal box next to the PIN diode may be used to allow ionising radiation to pass into the detector with minimal attenuation or energy deposition whilst still excluding visible light from the detector and keeping the box "light-tight".

Power can be supplied from a 9 volt battery, for example.

More documentation to be written later...

Bill of materials:

Qty: Description: Digi-Key SKU

4 100 nF ceramic capacitor, 0805 311-1361-1-ND
2 47 pF ceramic capacitor, 0805 311-1107-1-ND
2 100 uF 16V tantalum capacitor, "C" package 399-5214-1-ND
1 1 uF ceramic capacitor, 0805 311-1358-1-ND

2 10M resistor, 0805 311-10MARCT-ND
2 10k resistor, 0805 311-10KARCT-ND
2 330 k resistor, 0805 311-330KARCT-ND
1 1M resistor, 0805 311-1.0MARCT-ND
1 4.7 k resistor, 0805 311-4.7KARCT-ND
1 1 k resistor, 0805 311-1.0KARCT-ND
1 100 R resistor, 0805 311-100ARCT-ND
1 BPW34 silicon PIN diode 475-1070-ND
1 LM358 Op-amp, SOIC package 296-1014-5-ND
1 BF245 JFET (through-hole TO-92) 568-5600-ND

1 9V battery P647-ND
1 9V battery snap connector BS6I-MC-ND
1 Small 8 ohm loudspeaker 458-1135-ND
1 Metal box, eg. mint tin.