Thermionic emission pattern from a hemispherical LaB6cathode of lang;110rang; orientation was made using an experimental setup similar to Martinrsquo;s experiment. The emission pattern from a clean surface has clearly indicated that the bright region consists of (100) spot surrounded by four (210) spots. This suggests that the bright spots (except for the center spot in the crosshyphen;over images observed for lang;100rang;, lang;110rang;, and lang;111rang; LaB6cathodes correspond to (210) spots as deduced by Oshimaetal. Emission patterns at different vacuum conditions are also observed to find that a specific emission pattern appears with good reproducibility corresponding to the change of vacuum condition, leading to existence of enhanced thermionic emission.
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