| 摘要 |
PURPOSE:To obtain a long-life detector which has low neutron sensitivity by setting the ratio of the number of atoms of the charged gas of an ionization chamber type detector and that of atoms of <235>U of enriched uranium to the best prescribed number. CONSTITUTION:The inside electrode 2 of an ionization chamber type detector 100 for neutrons in a nuclear reactor is connected hermetically to discs 10 and 11 at the circumferences of both its ends. Consequently, the amount of charged gas 8, such as He, for ionization from an exhaust and gas charging pipe 7 is limited to set to 0.45-1.8 the ratio of the number of atoms of <235>U in enriched uranium formed on the surfaces of the electrode 2 and an outside electrode 1 and that of atoms of He. When Ar is used as ionizing gas, the ratio is 2.3-9. This best ratio lessens a decrease in neutron sensitivity even during long-period use, so that the long-life detector for neutrons in the nuclear reactor is obtained.
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