This is one of the most sensitive tubes for its size (5.5" long x 0.52" diameter x 0.78" base diameter). It operates on 400 to 520VDC and works great with our G18410 Geiger Counter Kit. It is sensitive to beta and gamma radiation and here in Arizona this tube produces about 80 counts per minute from background radiation. New old-stock made in East Germany. Center pin is (+) and metal base is (-). Note: this has a very thin glass wall and is fragile!