GB790528A - Improvements in electric discharge devices - Google Patents

Abstract

790,528. Cold-cathode tubes. GENERAL ELECTRIC CO. Jan. 20, 1956 [Feb. 16, 1955], No. 2019/56. Class 39(1). The dark breakdown voltage rise in a cold cathode discharge tube containing an ionizable gas filling is reduced by adding a small proportion of tritium to the filling. The spark gap tube shown comprises a cylindrical vitreous envelope 1 to which are sealed feathered edged cups 2 of a metal having a coefficient of expansion as near as possible to that of the envelope material. A cylindrical mounting post 3 which serves also as a terminal is welded externally to each cup 2 and has a reduced diameter extension 4 projecting into the interior of the envelope. The end of the extension 4 is bored to accommodate the shank of a rivet-like member 5 which is locked in place by crimping at 6. A button 7 providing the discharge surface is welded to the rivet 5 and may consist of a pressed and sintered mass of tungsten-nickelbarium alloy. The filling is 84 per cent argon and 16 per cent hydrogen at a pressure of 670 mm. of mercury with the addition of 2 millimicrograms of tritium. At a reduced pressure of 200 mm. of mercury an even smaller amount of tritium is required, and a formula is given for calculating the mass of isotope required to provide a given radioactivity. The Specification refers to the prior art of inserting uranium oxide in the form of a suspension or paint on the inside of the envelope of a discharge tube which is dried or baked before sealing. Some 100 milligrams of uranium oxide are necessary to produce the same radioactivity as the small amount of tritium.