Electron-Bombardment Detection of Noncondensable Molecular Beams

An electron-bombardment detector developed for the detection of noncondensable as well as condensable molecular beams is described. The ionization efficiency for a hydrogen deuteride beam is in the range of 10−5 to 10−4. Auxiliary components include: vacuum buffer chambers for source background gas reduction; a mass spectrometer for ion mass selection; an electron multiplier, electrometer, and phase-sensitive detector combination for signal observation. Modulation techniques for beam and magnetic resonance detection are discussed. Efficiencies, background problems, and relevant noise sources are included in a discussion of operational characteristics. A resonance line trace produced by at most 3% of a total HD beam is presented to demonstrate the signal to noise ratio at low signal levels. The system has effectively detected beams of permanent gases such as HD, D2, and Ne.