Scintillation characteristics of plastic scintillators using 9,9-dimethylfluorene as a host material

Plastic scintillators offer a fast response and excellent processability. However, they have a low scintillation light yield (LY) of approximately 10,000 photons/MeV in contrast to widely used inorganic scintillators. One reason for this is the relatively large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in polymer hosts such as polystyrene (PS) and polyvinyl toluene, which are commonly used in plastic scintillators. In this study, to improve the LY, we prepared PS-based plastic scintillators containing 9,9-dimethylfluorene (MF), which has a smaller HOMO–LUMO gap than PS. The MF concentration was varied over a wide range of 0−40 wt% relative to the total mass of the plastic scintillators. The addition of MF as a component of the host material increased the LY at an MF concentration of 30 wt% by approximately 27% for samples containing only 2,5-diphenyloxazole (DPO) as the fluorescent molecule and by approximately 34% for samples containing a wavelength shifter (1,4-bis(5-phenyl-2-oxazolyl)benzene: POPOP), compared with that of the corresponding MF-free samples. By optimizing the PS to MF mass ratio and the DPO-POPOP mixed powder concentration, the LY reached a maximum of 12,600 photons/MeV at a PS:MF mass ratio of 68:30 and a mixed powder concentration of 0.5 wt%, corresponding to approximately 1.3 times the LY of the commercially available EJ-212 (LY: 10,000 photons/MeV).