Our largest and most sensitive Geiger Counter uses a giant Russian Geiger Mueller Tube type CTC-6. This metal tube is super sensitive to beta and gamma rays. Here in Arizona the background count from this Geiger Counter is about 100CPM. The completely assembled board operates on one 9V battery (sold separately) and produces the familiar clicks and flashes of bright red light from an onboard speaker and LED. Size of board about 7.80" x 1.45". Tube may be slightly discolored because of age. No case available. Fully assembled and tested.