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19.7 × 5 × 5 cm

This tube is the vacuum head of a quadrupole mass spectrometer system produced in the 1980s for residual gas analysis.

In principle it allowed the operator to determine whether the gas still in a vacuum system was air from a leak or water or something else outgassing from the walls.

The location of a leak might be detected by spraying a gas of known molecular mass around suspected areas.

A quadrupole mass spectrometer (as opposed to a magnetic deflection MS) uses static and oscillating electric fields between four parallel metal cylinders to deflect away ions of any but one desired charge-to-mass ratio travelling down the axis of the device to a detector. Scanning the field parameters allows a mass (to charge ratio) spectrum to be generated.