Patent GB-845701-A (GB)
Title: Improvements in and relating to nuclear electric generators
IPC: G21H1/02
Filed: 1956-10-29
Abstract: 845,701. Cold cathode tubes; utilizing energy of radioactive substances. RADIATION RESEARCH CORPORATION. Oct. 29, 1956 [Oct. 27, 1955], No. 32977/56. Classes 39(1) and 39(4). In an electric generator of the type comprising an emitter electrode adapted to emit charged particles of low energy (not more than 200,000 e.v.) as a result of nuclear reactions and a collector electrode spaced apart in an evacuated envelope, the collector electrode comprises a member of which at least an outer layer bombarded by the said particles consists of a material of secondary emission ratio less than unity with respect to such bombardment. In general, a suitable collector material is an element of atomic number less than 10. In one form, Fig. 1, an emitter electrode and collector electrode 2 are mounted in an envelope 3 comprising a glass portion 8 sealed by a gasket 42 to a brass flange 9 to which is soldered a brass pipe 12 through which the envelope can be evacuated to a pressure below 0À1 micron of mercury so that " back " current produced by ionization is negligible. The emitter electrode 1 comprises a rod 10 of alloy, which constitutes the external positive pole of the generator, screwed into a brass block 11 which is soldered to a brass disc 4. Tritium gas which is an emitter of beta. particles is sorbed in a film 6 of zirconium which is deposited by evaporation onto a tungsten disc 5 which is held in a recess in the brass disc 4 by a ring 41. The collector electrode 2 comprises a microscopically porous carbon disc 60 supported on a brass disc 43 supported by brass spacers 45 on the flange 9 which constitute the external negative pole of the generator. The carbon may be commercial grade petroleum coke, wood charcoal, or any carbon or charcoal with microscopic porosity, but a disc formed by evaporating an aqueous solution of commercial colloidal graphite is unsuitable. In an alternative embodiment, the envelope comprises a nickel cylinder and end discs into one of which is soldered a copper exhaust tube. The emitter electrode comprises a copper disc onto which is evaporated a zirconium film in which tritium gas is sorbed, and the collector electrode comprises a carbon layer deposited on a nickel disc which is in contact with the envelope. The carbon layer may be replaced by an evaporated film of beryllium or lithium, but aluminium and chromium are unsuitable. In a further embodiment the envelope comprises a cylinder and one end plate of cold rolled steel and a further end plate of iron-nickel alloy. The emitter electrode comprises an axial molybdenum rod on which is deposited a film of titanium in which tritium gas is sorbed, and the collector electrode comprises a cylinder of porous carbon in electrical contact with the envelope. In the embodiment shown in Fig. 5 the glass envelope 62 is evacuated through a tube 63. Further reduction of the pressure may be effected by flashing a getter such as zirconium powder. Alloy rods 55 and 58 form the external poles. -The emitter electrode comprises a cylinder 56 of nickel foil, irradiated in a reactor to form " nickel 63," spot welded to an end plate 57 of stable nickel which is brazed to the rod 55. The collector electrode comprises an outer porous carbon cylinder 54 connected by a copper wire 52 to an inner porous carbon collector 53 secured by means of a nut to a threaded nickel rod 59 which is brazed to the rod 58. In the embodiment shown in Fig. 6 the envelope comprises a cylinder 34 and end discs 33 and 64 of alloy. The emitter electrode comprises a cylinder 39 of nickel foil, which may be stable nickel or " nickel 63," coated on both sides with evaporated layers 44 or 50 of zirconium in which tritium gas is sorbed, and supported by ceramic spacers 67 and 68. A nickel wire 66 connects the cylinder 39 to an alloy rod 31 forming the external positive pole. The collector electrode comprises a rod 37 and cylinder 35 of stainless steel on which layers 36 and 69 of lithium are deposited by evaporation. A plurality of emitter and collector electrodes may be mounted parallel to each other in a single envelope and connected in different series and parallel combinations as required. U.S.A. Specification 2, 527, 945 is referred to.