Geiger Counter - Radiation Sensor (Adafruit 483) Geiger–Müller counter

http://mightyohm.com/blog/products/geiger-counter/

Detect particles and/or make a cool random number generator with this handsome Geiger counter kit. This easy-to-make pack of parts turns a simple Geiger-Muller tube (included) into a portable blink, beeping radiation detector. You can also connect an FTDI friend to the header, to get serial output for datalogging on your computer. 

We put this kit together in a couple of hours and hand lots of fun bringing it around and listening for ticking sounds near our smoke detectors, bananas, countertops, Brazil nuts, chunks of Uranium, etc. It includes all components (PCB, tube, & parts) but you will need basic soldering tools and two AAA batteries to complete it. 

Please note! This Geiger Counter kit is for EDUCATIONAL PURPOSES ONLY. Don't even think about using it to monitor radiation in life-threatening situations, or in any environment where you may expose yourself to dangerous levels of radiation. Don't rely on the collected data to be an accurate measure of radiation exposure! Be safe!