Russian Geiger tube type CI-21BG is a glass type 70mm x 10mm diameter - 350V to 450V operating voltage tube. It detects beta and gamma rays and here in Arizona it produces a background click rate of 1 per minute. New Old Stock. Item has been tested prior to shipping. Note: This tube is meant to detect high levels of gamma radiation so it will not be as sensitive as an SBM-20 or STS-5. This will work with our C8600ASB Geiger Counter (sold separately).