| 摘要 |
PURPOSE:To stably radiate an electron beam for a long time by impregnating an ion impact resisting high melting point heat resisting material with an electron emitting material having a relatively small work function and a high electron emitting current density. CONSTITUTION:A hot cathode 1 contains an ion impact resisting high melting point heat resisting material 2 and an electron emitting material 3 operable at low vacuum and low temperature having a low work function selected from yttrium boride, lanthanum boride, cerium boride, cesium oxide and cesium boride. As the material having high resistance to ion impact, metals having melting points of 2400 deg.C or more (for example, tangusten, rhenium, osmium, tantalum, molybdenum, niobium and iridium) or carbides of these high melting point heat resisting metals, or borides of these high melting point heat resisting metals. Since zirconium has a low melting point as the metal, but its carbide and boride have melting points of 3000 deg.C or more, it can be used as the material 2. |
