I hope building a Geiger Counter Project is just fun and not a necessity but if you are feeling curious here is a cool DIY Geiger Counter project kit.
Via: Dangerous Prototypes
“The Geiger Kit is a board that provides the electronics needed to run, and detect events from the GM tube, along with a microprocessor (ATmega328) that makes it easy to customize a solution for processing and outputting the events. Both the Geiger circuit and the processor can be used independently of each other if desired.”