Russian military compact Geiger Muller Tube SI-3BG for detecting ionising radiation. Can detect beta and gamma radiation. The tube is intended for very high radiation levels and will show little reaction to natural background, also due to the low detection volume and materials used.
Notes on sensitivity:
The SI3BG tube is suitable for use with powerful radiation sources or for severe nuclear incidents resulting in high radiation doses. It makes no sense to use it for your DIY experiments, as the background radiation CPM on this tube is close to 0:
As you can see in the chart above, the average of the background readings over a period of 24 hours, barely reach 0.19CPM (each point in the chart was computed using another average of 60 independent, consecutive measurements. The dosimeter used to take the measurements has 1 minute resolution).
Background readings: 0.19CPM for a background radiation level of 0.12uSv/h, and these values are highly unreliable for small radiation doses due to the small sensitivity of this tube (it’s hard to sense fine variations with an un-sensitive=low resolution measuring tool). Longer time measurements are needed.
Working Dose Range: 300R/h (very high!)
Working Voltage: 380-460V
Working Current: 0,015-0,02 mA
Plateau Length/ Inclination: 80V/0,25%/V
Sensitivity to Gamma Radiation: 188 – 235 Pulses/s/R/h
Own Background: 0,2 Pulses/s
Working Temperature Range: -50 to +60 С