Neutron accelerator tube having improved ionization section

A neutron accelerator tube having a target, a spaced replenisher section for supplying accelerator gas, and an ionization section located between the target section and the replenisher section is claimed. The ionization section comprises: (a) an ionization chamber adapted to receive accelerator gas from the replenisher section, (b) first and second cathodes spaced from one another and having opposed active surfaces exposed to the interior of the chamber, and (c) an anode located at a position intermediate the cathodes whereby, in response to an applied positive voltage, electrons created by field emission are transmitted between the opposed active surfaces of the cathodes and produce the emission of secondary electrons upon impacting an active cathode surface. The active surface of at least one of the cathodes is formulated of a material having a secondary electron emission factor of at least 2