| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an electron radioactive material to the tip of a negative electrode stably. <P>SOLUTION: A body part 14A is constituted by tungsten including thorium oxide. A sinter junction layer 14B is constituted by tungsten having coarsened crystal grain in comparison to that of the body part 14A. The grain boundary diffusion in the sinter junction layer 14B is suppressed by covering the body part 14A including thorium with the sinter junction layer of the tungsten of the coarsened crystal grain that does not include thorium. In addition, a liner grain boundary 14D is formed between the body part 14A and the sinter junction layer 14B of a negative electrode 14. Therefore, the liner grain boundary diffusion of the grain boundary 14D is caused by the supply of thorium. <P>COPYRIGHT: (C)2012,JPO&INPIT |
