PURPOSE: To avoid breaking away of a coating layer so as to reduce scatter of electronic emission characteristics by arranging a metalic layer with a melting point lower than that of Os or Ir on the surface of an impregnated cathode and laying a layer of Os or Ir on it.
CONSTITUTION: In an impregnated cathode with a coating of Os film or Ir film, a metallic layer with a lower melting point than those of Os or Ir is provided in an intermediate portion between a coating layer and a cathode portion. The thickness of the film between 1,000W2,000 is practically appropriate. Thus, adhesion of Os film or Ir film to the impregnated cathode becomes good, and scatter of emission characteristics can be decreased.
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