| 摘要 |
PROBLEM TO BE SOLVED: To prevent slight drop of the sensitivity of a neutron detector to neutrons in the initial stage by applying a neutron sensitive material to electrodes after a neutron absorbing material having a specific neutron absorption cross section is mixed at specific reactivity. SOLUTION: The neutron sensitive material 3 is applied to a high-voltage electrode 1 and signal electrode 2 after a neutron absorbing material 4 having a neutron absorption cross section of about 50-1,000 barn is mixed in the material 3 at a mixing ratio of, for example, <=3% in reactivity. Since the material 4 which does not cause any nuclear reaction nor generate any charged particle even when neutrons come into collusion with the material 3 is mixed in the material 3 applied to the electrodes 1 and 2, a part of the neutrons made incident on a neutron detector is absorbed to the material 4 and the number of neutrons which cause unclear reactions becomes smaller. In order to prevent the slight drop of the detector to neutrons caused by gas absorption in the initial state of use, the kind and quantity of the material 4 are decided so that the material 4 can be burnt entirely in the initial stage. Namely, the neutron absorption cross section and mixing ratio of the material 4 are respectively adjusted to about 50-1,000 barns and <=3%.
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