Modern oxide-coated cathodes have the characteristic that the initial high electron emission decreases gradually with time of operation. This characteristic is avoided by using initially-uncoated cathode members to which a coating material is dispensed at uniform rate from a "dispenser" located within the common heat-shield. Such cathodes, after initial aging, show an electron emission equal to the initial emission of oxide-coated cathodes, which does not decrease with time. In the cathodes which have been tested, the dispenser was a closely woven "stocking" of fine molybdenum wires, filled with granules of fused BaO—${\mathrm{Al}}_2$${\mathrm{O}}_3$ eutectic. It was maintained at 1150°C by current through it, and served as a radiation heater for the cathode. The electron-emitting members were clean molybdenum. These cathodes show undiminished electron emission at the end of three years life test with no indication of exhaustion.

• Received 13 May 1939

DOI:https://doi.org/10.1103/PhysRev.56.86