MST-17 / MCT-17 Geiger Müller Counter Tube w/ mica window NOS & Tested

Description

MST-17 / MCT-17  Geiger-Müller Counter Tube w/ mica window and removable cap. NOS & Tested. Sensitive to alpha, beta (>0.16 MeV)
, and gamma radiation. The data and certification sheet is in Russian. To the best of my knowledge, the following are the tube's specs:
Voltage of start of counting:
< 1600V
Operating voltage (recommended):
1620 – 1740V
Length of flat part of counting curve (
plateau
):
150 V
Slope of the counting curve:
< 0.05%
Own background:
< 0.41 counts/s
Maximum radiation:
10,000 counts/min
Load resistance:
7-10 MegOhm
Allowable stray input capacitance:
< 10 pF
Working temperature range:
-30…+50 C
Anode material:
Platinum
Mica window
thickness:
< 5 mg/cm2
Weight:
~20g
Dimensions:
counter length 100mm, diameter 40mm
Mica window diameter:
20 mm.
I tested the tube near the middle of the recommended operation voltage range (1,700V) with a Nucleus Model 500 Nuclear Scaler (not included in this auction). As the pictures show, the background radiation, measured over a 10-minute period, amounted to about 180 impulses (or 18 impulses/minute) here in central Wisconsin. Predictable for this measurement, the presence or absence of the metal cap made no significant difference. A uranium-oxide glazed pepper shaker next to the side of the tube resulted in 1,271 impulses/minute. When a small amount of Americium-241, emitting about 1 uC of alpha radiation with particle energies of about 5.4 MeV, was placed about 1 cm away from the uncovered window, the counter registered 1,536 impulses/minute. The count dropped to125 impulses/minute with the cap, which contains a small hole, covering the mica window. (The remaining above-background radiation may be due to the small hole or the beta and gamma emissions In the decay chain.)
While the tube is NOS, there are some signs of tarnish on the brassy part (front of tube that frames the window and cap). I polished the outside of the cap with very fine sandpaper to remove the tarnish.
I will NOT send this tube via airmail since I'm worried that a non-pressurized cargo environment might cause damage to the mica window. (It happened to a similar type of tube I had purchased in Europe.)