Scintillation Type Mass Spectrometer Ion Detector

A new and relatively simple type of mass spectrometer ion detector is described. The positive ion is accelerated onto an aluminum surface releasing secondary electrons, and these in turn are accelerated onto an organic scintillator, viewed by a sealed-off photomultiplier. Counting methods are used to measure the ion beams. The detector has a low noise level, 4×10−20 amp, and the mass discrimination is small for ions in the high and low mass range. Admission of air to the vacuum system does not affect the gain of the detector, since no activated surfaces are situated within the vacuum. In the event of a fault occurring in the photomultiplier a new one can be substituted in a few minutes without letting air into the vacuum system.