The performance of single-crystal LaB//6 cathode was examined by measuring the brightness and current stability under the same conditions as for the conventional W hairpin cathode. The LaB//6 cathode was mounted in Vogel-type electron gun assembly of an electron probe microanalyser JAX-3 specifically modified for this purpose. The result shows that the present LaB//6 cathode provides not only high brightness of 2 multiplied by 10**5 A/cm**2 str. at 20 kV, but also high-current stability better than 1 multiplied by 10** minus **3 Ah** minus **1 in standard operation without any specific aid for current stabilization. Thus an order of magnitude increase in both the brightness and service lifetime can easily be obtained provided that the vacuum of the system is adequate, namely better than 1 multiplied by 10** minus **5 Torr (1. 33 multiplied by 10** minus **3 Pa). This substantial improvement of the present single-crystal LaB//6 cathode over the conventional W hairpin was also confirmed in a practical way by use in a commercial-type scanning Auger electron microscope, JAMP III.
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