Chrono wrote in to share PiGI, a Geiger-Müller breakout board compatible with the RPi.

The Raspberry Pi is a perfect platform to be a cheap but very versatile geiger counter. It can be connected to a TV/Monitor to display a nice graphical interface, it can play the nostalgic tak, tak, taktaktak sound via audio output and it can also serve as an autonomous geiger counter sensor node (even solar powered) collecting and sharing real-time and historic data.

Check out the GitHub repository if you want to learn more.