Use a Cheap PIN Diode as a Geiger Counter

After the Fukushima nuclear power plant disaster, radiation measurement became newly relevant for a lot of people. Geiger-Müller tubes, previously a curiosity, became simultaneously important and scarce.

Opengeiger.de (English-language version here) has complete instructions for making a Geiger counter without a Geiger-Müller tube. Instead, this counter uses a PIN photodiode and some carefully chosen operational amplifiers. The total cost of such a device is significantly cheaper than the alternative: under $1 for the diode and around $5 for the rest. And since the PIN photodiode in question is used in many other devices, it’s not a niche component like a Geiger tube is.

The secret sauce is in component selection and tuning. Opengeiger uses the BPW34 diode because it is relatively common and has a large surface area, but also because it has a very low capacitance when reverse-biased. The first-stage opamp choice is also fairly critical. Considering that an average gamma radiation event produces only around 10 nanoamps for about 50 microseconds, a lot of amplification (100,000x), low noise, and high bandwidth are a must.

If you want to get started with this project, you could first browse through the explanation (PDF) to get an overview of the project’s goals, read up on all the technical considerations (PDF) or just head straight for the DIY instructions for the “Stuttgarter Geigerle” (PDF, schematic is on the last page). All of the documentation is chock-full of relevant references and totally worth the read.

Gamma-ray scintillation probe in a paint can

gamma.ray.scintillation.probe.in.paint.can

The [Prutchi] family sounds pretty cool. [David], the father, is a well educated engineer, has 70 patents, and has written two books. On his off time, he has a passion for making experimental physics accessible to the average Joe. His daughter [Shanni] is a high school student who co-authored one of those same books, and helps conduct research in the fields of Radio-Astronomy and Quantum Physics. Together, they came up with an affordable, yet very sensitive, gamma-ray scintillation probe for their customized Civil Defense V-700 radiation survey meter. Sweet.

They decided to use parts that were low cost and readily available so others could easily follow in their footsteps. A Philips XP5312/SN photomultiplier tube (PMT) and scintillation plastic are the main components.  The enclosure for the probe is a standard paint can, lined with polyurethane foam inserts to help protect the assembly and hold everything in place.

[David] says that since the probe is very portable and has a high level of sensitivity, it is an ideal candidate for radioactive mineral surveying and scouting miscellaneous gamma-ray sources. They documented the whole process and have compiled a handy PDF file for those who are interested in creating their own.