Type SI-39G glass geiger mueller tube made in Russia. This operates from 360 to 440VDC and detects beta and gamma rays. The tube is new and we test every one 100% before shipping. These work perfectly with our C8600 or G18410 Geiger Counter Kits (not included). Here in Arizona we measure about 8 to 10 clicks per minute background radiation with this tube and our C8600 or G18410 kit.