The Type 5 Pocket Geiger Radiation Sensor from Radiation Watch is a highly sensitive radiation sensor designed for the embedded systems market. Capable of detecting Gamma and Beta radiation, this sensor has a simple pulsed output that can be used with any microcontroller. Radiation Watch has a handful of documents and example Arduino code to get you up and running. They have also written a Windows example program in C# (source included!) to output graphs to a computer using an Arduino as the reader.
These small Geiger sensors feature a measurement range of 0.05uSv/h to 10mSv/h at 0.01cpm to 300Kcpm with a required measurement time of two minutes. The Pocket Geiger has an onboard DC boost circuit, so the board can be supplied with a friendly 3V to 9V. Using only 30mW (10mA @ 3V), it is very low power. Additionally, the counter comes with an optional enclosure and 3.5mm cable.
Note: This product is for educational purposes and should not be directly relied upon for determinations regarding one’s health or safety.