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Summary form only given. The oxide-coated cathode is still the most widely used electron emitter in CPTs thanks to its low cost and excellent emitting properties. Both the emissive oxide and the base metal vary from one manufacturer to another. Schematically, this cathode is composed of a 60 to 150 thick nickel alloy substrate called the base metal, covered with a 50 to 100 thick porous layer of alkaline-earth oxide. Depending on the desired application, the coating and the base metal can be optimised so as to get the best emitting properties. Long-term life tests were run in CPTs in standard and stressful conditions and emission performances measured. Several types of base-metal were compared. The influence of the nature of the base-metal and its chemical composition (reducing elements contents) on life was studied. The effect of temperature will be also discussed. The results obtained allow proposing an optimised bimetal ensuring excellent longevity of the cathodes. They also give an insight into the mechanism of operation of the oxide cathode.