Improvements in and relating to apparatus for separating charged particles of different mass-to-charge ratios

摘要

698,850. Heavy-ion beam tubes. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 30, 1951 [Dec. 2, 1950], No. 28162/51. Class 39(i) A device for separating charged particles, i.e. ions, of different mass-to-charge ratio comprises a source of ions, an electrode for collecting such ions which have a predetermined ratio of mass-tocharge, means for producing an alternating electric field in the vicinity of the source of ions, and an electrostatic field in the path between the source of ions and the collecting electrode, there being also provided a means for grading the electrostatic field so that at any point of the path the increment of the field strength is substantially linearly related or the voltage is substantially parabolically related to the distance of that point from the source of ions, and a means for detecting or measuring the current caused by the ions impinging on the collector electrode. In the embodiment shown in Fig. 2 a thermionic filament 19 surrounded by a light-shield 24 projects electrons into an electron-trap electrode 27 and produces ions by collision. Grading electrodes are arranged on either side of the ion source and are connected together internally by resistances so that when a battery 61 is connected between the outermost grading electrode 43, 47 and the innermost electrodes 30, 31 a parabolic electrostatic field is-produced between the ion source and the collector electrodes 13, 14. A high frequency alternating potential is applied between electrodes 30, 31 from an oscillator 38 and it is explained in the Specification that, owing to the parabolic field, only ions of a particular charge to mass ratio can reach the collector electrodes, the particular charge to mass ratio depending on the frequency of the oscillator 38. Magnetic focusing coils 69, 70 may be provided. In a modification, Fig. 4 (not shown), the alternating potential is applied in series with the battery 61 between the inner and outer grading electrodes. In a further modification, Fig. 8 (not shown), the ion source is displaced to one side of the median plane of the device and the alternating potential is applied between two grading electrodes adjacent the median plane. In another embodiment, Fig. 3, the grading electrodes are omitted and the parabolic field is obtained by making the collecting electrodes 75, 76 in the form of hyperboloids of revolution; the alternating field may be applied between two electrodes 30, 31, or these may be omitted and the alternating potential is then applied to the collecting electrodes in series with the battery 61, Fig. 7 (not shown).