Polystyrene is the main component of plastic scintillator, and absorbs radon as well as liquid aromatic solvents. I proposed a new radon monitor which detects radon distributed into plastic scintillator. As a preliminary experiment, plastic scintillator was put in a counting vial together with radon water and was measured by liquid scintillation counter. It was found that the scintillation spectrum of radon series was observed and the counting rate was proportional to the radon concentration in water. Then the radon concentration in water could be measured by plastic scintillator absorbent of radon. This method, APS: Absorptive Plastic Scintillation counting, is practicable to continuous radon monitor for environmental research.
I evaluated the performance of a highly reflective multi-layer optical film (MLOF) for a reflector of scintillators for PET by comparing it with a white Teflon tape. The scintillators used for evaluation were BGO, GSO, LSO, and LGSO. Scintillators covered by the MLOFs showed similar light outputs as those rapped by the Teflon tapes. In addition to the highly reflective characteristic, the thin thickness of the MLOF makes it possible to arrange the scintillators with minimum dead spaces, and it is concluded that the MLOF is quite useful for reflector for PET scintillators.
Silicon avalanche diode was tested as new fast detector for positron annhilation experiments. The timing signal is initiated by a positron passing directly through an avalanche diode. Obtained time resolution is comparable to that obtained with a conventional plastic scintillator and photomultiplier tube. A β+-γ coincidence positron lifetime spectrometer was constructed by using an avalanche diode as the detector for start signal and an excellent time resolution, 240 Ps (FWHM), for the total system was accomplished.