SI-19BGM Possibly the smallest end-window GM tube in the world?

SI-19BG (M) SI19BGM СИ19БГМ

 

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 close to the window.

The specifications are a bit sketchy and I can't find a datasheet with the proper specs. These are from the ebay listing:

• SI-19BGM geiger tube is designed to detect betta, gamma
• Sensitivity Radiation                 1000-1500 Pulses/s/R/h
• Plateau  Inclination                   0.25%/V
• Working Voltage                       360-440V
• Maximum registering range       900 Roentgen/hour
• Length                                     20mm
• Diameter                                 9.3mm
• Weight                                     4 grams

At first I tried it with about 400v (~405v) and a 4.7M resistor, but it was counting too much (avalanching?). I changed the anode resistor for a 10M resistor and that seemed to calm it down quite a lot. I think this is probably better in the 380-390v range, and I'll test that at some point.

You can download hi-res pictures here.

 

 

 

The next images show it next to a CR2032 battery and an Am-241 button.