| 摘要 |
PURPOSE:To reduce a background noise and detect a minute amount of radioactive rays with a good signal-to-noise ratio by providing a radioactive ray shield close to the inner side of a sealing member to seal up the end opening of a cathode pipe. CONSTITUTION:An electron tube is composed by providing a cathode pipe 12, an anode pin 14 penetrating through the cathode pipe 12 in the axial direction, lead soft glasses 16 to seal the openings 12A and 12B on both ends of the cathode pipe 12, and the like, and it measures the radioactive ray amount incident into the cathode pipe 12. And at the inner side of the lead soft glasses 16 or the like to seal the both end openings 12A and 12B of the cathode pipe 12, radioactive ray shields 18 are provided to shield the radioactive rays generated spontaneously from the lead soft glasses 16 and the like, and their incidence to the measuring space in the cathode pipe 12 is prevented. Consequently, a background noise is reduced, and a minute amount of radioactive rays can be detected with a good SN(signal-to-noise) ratio.
|
