Patent GB-1130145-A (GB)
Title: Improvements in or relating to magnetically confined electric discharge apparatus
IPC: H01J41/20
Filed: 1965-12-30
Abstract: 1,130,145. lonization groups; getter-ion pumps; ion sources. NIHON SHINKU GIJUTSU K.K. 30 Dec., 1965 [30 Dec., 1964; 8 Jan., 1965], No. 55238/65. Heading H1D. In a magnetically confined electric discharge apparatus such as an ionization gauge or getter-ion pump ionizing electrons are derived in the ionization region between anode and cathode electrodes from a surface which emits electrons under irradiation by radioactive material. In a getter ion pump, Fig. 1, comprising a hollow anode 20f and upper and lower cathode plates 15f, an annular radioactive plate 56 is secured through an intermediate annular non-radioactive plate 54 to the underside of the lower cathode plate adjacent a bore 52 provided in the lower cathode plate. The outer casing 12f is of stainless steel and emits electrons in the region 58 which pass through the bore 52 to the ionization space 36. The radio-active material is preferably Ni<SP>63</SP> or Sr<SP>90</SP> emitting #-rays. The bore 52 may be located at the centre of the cathode plate instead of off-centre. The radio-active source may be located, Fig. 4 (not shown), at position 58, on the inner surface of the casing 12f, instead of at 56 and an electrostatic field may be set up around the bore 52 to prevent the passage of low velocity electrons. The lower cathode plate may be a reticulated plate and a plurality of radio-active elements may be provided on the inner surface of the casing. In a modification, Fig. 2 (not shown), with a cylindrical openended cathode (15g) surrounding a central rod anode (20g), a radio-active element (28g) is mounted on the inner surface of the cathode and auxiliary annular end-plates- (58g) are provided which emit electrons in response to the radioactive radiation. The cathode and anode may be interchanged. In another modification, Fig. 3 (not shown), with a cylindrical openended anode (20h) and upper and lower cathode end-plates (21h, 23h), a radio-active element (28h) is mounted in line with the lower cathode end-plate and an auxiliary, electron-emitting, electrode (58h) is mounted in line with the upper cathode end-plate. In all these embodiments the cathode is composed of, or contains, Mo, Cr, W, Ta, Nb, Fe, Ti, Zr, Ni, Ba, A1, Th, Mg, Ca, or Sr, and/or a material coated with such a substance, while the anode is composed of a reactive substance or of stainless steel. The auxiliary electron, emitting electrodes or plates may comprise the oxide, carbide or boride of an alkaline earth metal or sheet-metal coated with such substance and may contain a radioactive substance. The radioactive element may be constituted by such composite element. A suitable composite element may comprise Ni<SP>63</SP> with a film of Si or Ge. In an ionization gauge, Fig. 5, comprising an open cylindrical cathode 116 provided with a plurality of openings 115 and a surrounding open cylindrical anode 117, a plurality of radioactive sources 121 are secured to the inner surface of the cathode around the circumferences of the openings 115 and an inner auxiliary, rod electrode 114 is the electron emitter. The anode and cathode may comprise Mo, Re, W, Ta, Fe, Ni, Pt, Au, Ir, Al or Cu and/or alloys thereof and the auxiliary electrode 114 may comprise any of these substances and/or the oxides, carbides or borides of alkaline earth metals. The anode, cathode and auxiliary electrode may be lined with these substances. Preferably, the anode and cathode comprise Pt or Au coated Mo, and the auxiliary electrode W lined with ThO 2 . Ni<SP>63</SP> is used for the radio-active sources. In a modification, Fig. 7 (not shown), the anode and the auxiliary electrode are interchanged with the radiation sources (121a) provided on the outer surface of the cathode (116a) and in a further modification. Fig. 8 (not shown), the auxiliary electrode is constituted by an envelope casing (114b). In another modification, Fig. 9 (not shown), a rectangular frame anode (117c) is located between upper and lower cathode plates (116c<SP>1</SP>, 116c<SP>11</SP>) and a radio-active source plate (121c) and an auxiliary electron emitting electrode plate (114c) are located to one side of the anode-cathode assembly with the radio-active and auxiliary plates (121c, 114c), respectively, in line with the lower and upper cathode plates (116c<SP>11</SP>, 116c<SP>1</SP>). In another modification, Fig. 10 (not shown) having an anode-cathode arrangement and an outer casing generally similar to that of Fig. 1, a bore (115d) and a radio-active source (121d) are provided off-centre of the upper cathode plate (1 16d<SP>1</SP>) and an opening (140) is provided at the centre of the lower cathode plate (116d<SP>11</SP>) through which ions travel to a collector (143) located at the bottom of a tubular extension 141 of the envelope casing. The ion current is a measure of the constant current due to the "ionization of neutral molecules. A mesh electrode may be provided just below the opening (140) in the lower cathode plate (116d<SP>11</SP>) to prevent the escape of electrons and the ion collector (143) may comprise an electron multiplier. Additional electron repelling grid electrodes may be provided between the cathode plates. Ion sources.-Mention is made of the application of the invention to ion sources for mass spectrometers on partial pressure detectors.