| 摘要 |
PURPOSE:To enable the radioactivity concentration of beta rays and gamma rays to be independently measured by one measuring instrument by providing a plurality of beta ray detecting scintillator plates mounted in parallel in a gas chamber and a gamma ray detecting NaI(Tl) crystal wholly sealed by a transparent material. CONSTITUTION:A radiation detector 10 is comprised of a plurality of beta ray detecting plastic scintillator plates 12 mounted in parallel in a light shielding gas chamber 11, a gamma ray detecting NaI(Tl) crystal 14 mounted also in the gas chamber 11 and wholly sealed by a transparent glass plate 13, a photomultiplier 15 closely mounted to the crystal 14 and the like. The scintillator plate 12 is extremely thin and sensitively emits light only in response to beta rays. On the other hand, the crystal 14, since sealed by the glass plate that shields betarays, is sensitive only to gamma rays. A light emission from the scintillator plates 12 and the crystal 14 due to beta rays and gamma rays, respectively, are captured by the photomultiplier 15 and independently taken out via a pulse-height discriminating circuit and the like to be counted in a radioactivity measuring circuit.
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