Russian SI-3BG / CI-3BG glass Geiger Mueller tube is designed for detecting Gamma radiation. Overall length of tube including metal end caps is 2.2" L x 0.32" diameter. This tube operates from 360V to 460VDC. This tube works with our C8600ASB Geiger Counter Board. The background radiation using this tube in Arizona is about 3CPM. New very old stock! Each tube is tested before we ship!