| 摘要 |
PURPOSE:To enhance sensitivity and to reduce background counting by coincidence counting beta-rays and annihilation gamma-rays by two or more detectors using scintillators easily permitting beta-rays to transmit and having high density. CONSTITUTION:The beta-rays from a tube 10 through which blood passes are absorbed by a plastic scintillator 12a to be converted to light which is, in turn, measured by the PMT (photosensor) 12b of a side surface. Annihilation gamma-rays emit fluorescence by the opposed scintillator 14b provided on the outside to be measured. The signals of the scintillator 12a and the opposed scintillator 14a are coincidence counted by a coincidence counting circuit 22 through respective PMTs 12b, 14b. By this method, even when the threshold of beta-rays is set low, the coinicidence counting with gamma-rays is performed to make the effect of a background hard to receive and, in the same way, the background counting due to the coincidence counting of scattering gamma-rays can be also removed. By this method, the measuring sensitivity of radioactivity is enhanced and background counting is reduced and the shielding of lead can be reduced and miniaturization and wt. reduction can be achieved.
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