| 摘要 |
PURPOSE:To ensure high sensitivity detection of only epithermal neutrons. CONSTITUTION:A rod-like collector electrode 22 is arranged on the inside of a box-like outside electrode 20, and helium -3<3>He is sealed therein. The output of the collector electrode 22 is connected to a measurement circuit 30. A moderator 32 such as polyethylene is provided on the lower part of the outside electrode 20, and an absorption layer 34 made of rubber including boron is arranged on the entire circumference of a detector. Thermal neutrons are absorbed by the absorption layer 34 and are not detected thereby. Accelerated neutrons are transmitted through the absorption layer 34 as well as the moderator 32 and are not detected thereby. Since only epithermal neutrons of 0.5-5X10<4>eV are transmitted through the absorption layer 34 and is moderated by the moderator 32 into thermal neutrons, nuclear reaction occurs and ionized charges are generated, which are detected as pulses.
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