| 摘要 |
PURPOSE: To measure neutron flux density larger than a specific value by constituting electrodes in a 2nd group close to the center of an enclosure so that it is exposed to neutron flux density from electrodes in a 1st group provided nearby the periphery of the enclosure. CONSTITUTION: The enclosure 2 in the fission chamber 6 is filled with a gaseous medium and the cylindrical electrodes 8 and 10 in the 1st group and the electrodes 10 and 12 in the 2nd group (where the electrode 10 is common to the two groups) which have their center axes on an X axis are provided while insulated from each other. The surface of the electrode 8 facing the electrode 10 is coated with a fissible substance deposit layer 14 which has high surface mass or surface density and the surface of the electrode 12 which faces the electrode 10 is coated with a fissible substance deposit layer 18 which has smaller surface density than the deposit layer 14. Consequently, when the chamber 6 is placed nearby a reactor core, the ratio of neutrons detected by the electrodes 10 and 12 and a current due to spuriousγrays increases and the linearlity of an electric signal is optimized, so that neutron flux of about >=12 decades can be measured.
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