PURPOSE:To enable a BF3 proportional counter to operate under intense radiation over a long period by charging the counter with a porous getter having a molecular diameter larger than that of fluorine gas and smaller than that of BF3 gas in order to adsorb only fluorine gas selectively. CONSTITUTION:In an neutron detector, a linear anode 1 and a cylindrical cathode 2 are concentrically installed electrically insulated from each other. A case consisting of the cathode 2 and terminal plates 3a and 3b made of an insulating material is charged with BF gas through a pipe 4. An electric-signal-drawing connector 6 is attached to the terminal plate 3b to connect the anode 1 to the connector 6. The inner surface of the cathode 2 is coated with a getter consisting of zeolite, for example a molecular sieve 8 of 3-4Angstrom hole diameter. Since the molecular diameter of fluorine gas is about 3Angstrom and that of BF3 gas is about 5Angstrom , the molecular sieve 8 can selectively adsorb only fluorine gas. Therefore a stable sensitivity characteristic and an excellent radiation resistance can be maintained over a long period.
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