Patent Number: 043107656
Section: claims

1. In a sealed neutron accelerator tube having a target and a spaced replenisher section for supplying accelerator gas, an ionization section located between said target section and said replenisher section comprising: (a) means forming an ionization chamber in said tube adapted to receive accelerator gas from said replenisher section,  (b) first and second cathodes spaced from one another and having opposed active surfaces exposed to the interior of said chamber,  (c) anode means located at a position intermediate of said cathodes whereby in response to an applied positive voltage electrons created by field emission are transmitted between the opposed active surfaces of said cathodes and produce the emission of secondary electrons upon impacting an active cathode surface, and  (d) the active surface of at least one of said cathodes being formulated by the heating in the presence of oxygen of a material having a secondary electron emission factor of at least 2, and said active surface is at least two atom layers in thickness. 2. The method of claim 1 wherein the active surfaces of both of said first and second cathodes are formulated by the heating in the presence of oxygen of a material having a secondary electron emission factor of at least 2. 3. The neutron accelerator tube of claim 1 wherein said active surface is of a thickness to be stable to ion impact. 4. The neutron accelerator of claim 1 wherein said active surface is mechanically secured to said cathode. 5. The neutron accelerator tube of claim 1 wherein said material is an alkali metal halide. 6. The neutron accelerator tube of claim 1 wherein said material is an alkaline earth metal halide.