GB777457A - Electron multiplier - Google Patents

Abstract

777,457. Electron multipliers; mass spectrometers; cathode materials. BENDIX AVIATION CORPORATION. Feb. 25, 1954, No. 5595/54. Class 39(1). An electron multiplier, particularly for use with a time-or-flight mass spectrometer, comprises two series of secondarily emissive plates 70-82 and 84-96 disposed back-to-back with electric and magnetic fields so arranged as to direct the secondary electrons from the last plate 82 of the first series to the first plate 84 of the second series, and an electrode 106 in the form of a grid interposed in the path of the electrons from the first series to the second series which shields the electric fields established between the plates of the second series from the electron fields established between the plates of the first series. The plate 70 has a width greater than that of any of the other plates. The electrode 106 is at a potential intermediate between that of the plate 82 and the plate 84. The successive plates in each series are laterally contiguous and relatively displaced perpendicularly to their planes and are at potentials so correlated with their respective distances from common electrodes 40, 108, preferably at ground potential, as to produce substantially equal electric accelerating fields between any two successive plates. More than one of the plates 70, 72, 74 of the first series are arranged to receive primary charged or uncharged particles, e.g. ions, neutrons, atoms and electrons, through the slot 42 and those plates 72, 74 which receive both primary particles and secondary electrons are arranged to yield a multiplication factor of about unity, whereas the following plates yield a multiplication factor of about two. The plates of the first and second series can be made from a beryllium-copper alloy having approximately 2 per cent of beryllium. The primary particles passing through the slot 42 can be ions produced in bunches by a mass spectrometer of the timeof-flight type substantially as described in Specification 767,527 and the electrons emitted by the last plate 96 are collected by the electrode 110 connected to an oscilloscope 46. Specification 727,683 also is referred to.