| 摘要 |
To prevent the deterioration in sensitivity of the photocathode (20) of an electron tube and maintain stable output for a long time, an ion confining electrode (22) and an ion trap electrode (23) are provided between the photocathode (20) and a first stage dynode (24a). The potential of the ion confining electrode (22) is set higher than that of the first stage dynode (24a), while the potential of the ion trap electrode (23) is set equal to or higher than that of the photocathode (20) and lower than that of the first stage dynode 24a. Since the feedback to the photocathode (20) of the positive ions generated in the vicinity of the first stage dynode can be effectively suppressed, the sensitivity of the photocathode (20) is prevented from decreasing, and stable output is maintained for a long time. <IMAGE> |
