I’ve bought this tube some time ago with other tubes from an ukrainian seller because of it’s price. Usualy it is sold at 2€ each. This tube is so small and cute but is… absolutely useless.

SI3BG russian geiger tube

If you try to measure the natural radioactivity or if you try to test barely radioactive samples like pechblende or uranium glass you’ll obtain CPM in the range of 4-5 for the natural background and 15-20 for a medium active pechblende sample.

Typical application circuit

It was made to test fallout from a nuclear explosion. I’ve seen is usen in russian personal counters to help other two SBM20 tubes when the situation is too hot. Practically, is just usefull for pocket counters/alarms for soldiers during a nuclear war.