30th Anniversary of the Chernobyl Tragedy – or – Building a PIN Diode Geiger Counter

Exactly 30 years ago a great disaster struck the region of Chernobyl: a nuclear accident occurred that released a large quantity of radioactive particles into the atmosphere. And it is only five years ago that, with the Fukushima Daiichi nuclear disaster, a second similar catastrophic event has taken place.

These anniversaries┬ádid not directly let me build a PIN Photodiode based Geiger Counter, it is more or less┬áa coincidence.┬áThe main drive to build such a device was my curiosity and (please forgive me)┬áa fascinating green glow I’ve seen on various fluorescent Uranium minerals under UV light.┬áBut in this context it should not be forgotten that at present there still is a significant increase in background radiation in some regions and some agricultural products due to these events.

There are lots of descriptions┬áof how to build such a device; even cheap commercial products (e.g. the Smart Geiger) use such a┬ádesign.┬áEspecially two sites caught my attention: OpenGeiger.de┬áand Das Gammastrahlen-Mikrofon┬á(German).┬áThe design I’ve chosen is based on these sources but I’ve begun to further modify it. In this post I’m showing the design I’ve started with. It mainly relies on two BPW34 (Vishay Datasheet) photodiodes connected in parallel, and two transistors┬áto amplify the voltage fluctuations of beta and/or gamma┬árays striking the diodes. A 9 Volt battery was added to increase the pulse height.

The common approach to protect the photodiodes from light is to use one layer of tin foil and connect it to ground. This should also protect the circuit┬áagainst electromagnetic radiation.┬áI’ve started with┬ásomething different and dipped the┬ádiodes three times┬áinto liquid rubber (Plasti Dip). My hope was to at least allow some beta particles to reach the semiconductor material.

Photodiode with Liquid Rubber Coating

So far I’ve tested the basic design shown above and had mostly noise on my microphone input. I’d say that sporadic crackling has more to do with the 1 hour hacked together design than beta or gamma rays. The liquid rubber seems to block of light, but the simple design is sensitive to electromagnetic radiation. Waving your hand or even movements in about 1 m distance is visible in the sound profile.┬áAn additional tin foil shield connected to ground did not change the noise profile, although the EMR influence┬áwas reduced. I’ve tested it with two different sound cards (microphone inputs).

I’m currently redesigning the whole approach┬áand expect better results. So stay tuned…

Smooth Newts

Today my sons and I went on one of our adventure tours in the Fr├Âttmaninger Heide (north of Munich, actually 10 minutes from our place). We were surprised to come across a few puddles that were full of smooth newts; around 6 or 8┬áper puddle. We’ve seen newts before in the Fr├Âttmaninger Heide, but we only expected┬átadpoles in puddles (there were plenty of them as well).Smooth newt in a small puddle Smooth newt next to a small puddle