Neutron accelerator tube having improved ionization section

A neutron accelerator tube is described haing a target section, an ionization section, and a replenisher section for supplying accelerator gas to the ionization section. The ionization section is located between the target and the replenisher section and includes an ionization chamber adapted to receive accelerator gas from the replenisher section. The ionization section further includes spaced cathodes having opposed active surfaces exposed to the interior of the ionization chamber. The active surface of at least one of the cathodes is formulated of a beta - emitting material. An anode is located intermediate the cathodes whereby in response to an applied positive voltage, electrons are transmitted between the opposed active surfaces of the cathodes and produce the emission of secondary electrons. The active surface of the other cathode may be formulated of a beta - ray emitter or of material having a secondary electron emission factor of at least 2. One cathode member located in the tube adjacent to the replenisher section may have a protuberant portion extending axially into the ionization chamber and formulated of a beta - ray emitting material. A portion of the active surface of the cathode which is recessed with respect to the protuberant portion may be formulated of a material having a secondary electron emission factor of at least 2. The other cathode spaced from the first cathode member in the direction of the target has an aperture therein along the axis of the protuberant portion