The use of radioactive tracer techniques in the study of cathode problems

Reasonably long-lived isotopes of barium strontium and calcium are available from the Oak Ridge Laboratories of the Atomic Energy Commission. If these are in­ corporated in oxide cathode coatings, a convenient means is available for studying a number of problems which arise in the operation of electron tubes utilizing oxide coated cathodes. Studies have been made of the evolution of material from oxide coated cathodes both during activation and life. It is found that the principle evaporant from equi-molar oxide coatings based on a pure nickel is barium oxide. The second most important evaporant is metallic strontium. It is believed that approximate equal amounts of barium and strontium metal are evolved but the barium metal evolved is masked by the evaporation of barium oxide. It is believed that under cert in circumstances the strontium itself may provide an index for the· reducing potentials of the base nickel. These techniques have also been applied in a study of the effects of cathode evaporation on the secondary emission ratio of a target exposed to an oxide coated cathode.