The VA-Z-115 geiger mueller tube is very sensitive to beta and gamma radiation. It requires about 450VDC for operation and works great with our G18410 Geiger Counter Kit. The tube is new old-stock made in East Germany during the Cold War. Size is about 3.23" long x 0.55" diameter (base flange is 0.83" diameter). The background radiation count here in Arizona is about 35 counts per minute. Center pin is (+) and metal base is (-).