This software is designed to work with the Arduino Uno and the Radiation Sensor Board for Arduino from Cooking Hacks, but should also work with your own hardware design if you adapt either your hardware or the software.
I suggest to take a look at the documentation of the Radiation Sensor Board, it gives a good summary on radiation detection and the hardware used (Especially the geiger-mueller-tube).
Download: TimeWaster's Geiger Counter v1.1
Older versions: TimeWaster's Geiger Counter v1.0
* v1.1: * - You can set your name * - Replaced main loop time calculation * - Replaced overflow check loop with interrupt * - More exact measurement * - Minor bugfixes * * v1.0: * - Initial release
Have fun and stay safe!