end-window tubes

SI-19BG (M) | SI19BGM | СИ19БГМ - Tiny end-window Geiger Muller Tube I received this today after waiting for it to arrive for a couple of weeks. Purchased from Ukraine (via eBay). Not only is it tiny, it is the most expensive GM tube I have bought yet per gram of weight! And it appears to work okay. Sensitive to Gamma and Beta. This tube really is remarkably small. The end window must be no larger than 6mm diameter and the whole thing is only 20mm in length. It's not sensitive and for the couple of minutes I had it on test, the background was about 4cpm and it went nuts with Am-241 being held