Here it is.
According to seller’s introduction, this is a Geiger-Muller tube from Ukraine. The parameters of this tiny tube are listed below.
Radiation determine: beta soft/hard gamma soft/hard
Voltage of start of counter: 260-320V
Operating voltage: 350-475V
Length of flat part of counting curve (plateau): 100V
Slope of the counting data: <0.15%/V
Own background: <1 imps/s
Working life: 50*10^10 counts
Dimensions: counter length 48mm, diameter 10mm
I should start preparing for a small high voltage supply for this tiny stuff 🙂