The luminescence from a cyclohexane solution containing p-terphenyl irradiated with 60Co γ-rays has been quenched by various compounds. The quenching efficiencies were found to be in the following order; sulfur hexafluoride∼carbon tetrachloride>nitrous oxide>ethanol>ammonia>carbon dioxide. These compounds are known in radiation chemistry as electron scavengers or as positive-ion interceptors. Cyclopropane and ethylene have also shown an appreciable quenching ability, but n-butane has shown scarecely any. These results have been explained by assuming that ionic reactions are responsible for the luminescence from a cyclohexane-p-terphenyl scintillator.

The luminescence from a benzene solution containing p-terphenyl induced by γ-ray irradiation has been compared with that induced by UV irradiation at 2500 Å in the presence of various quenchers. The quenching efficiencies of electron and positive ion scavengers (SF6, N2O, CO2 and NH3) were found to be greater for the γ-ray excitation than for the UV excitation, while 1,3-butadiene, which is known as a quencher for excited benzene, (1B2u), showed almost the same efficiency for both modes of excitation. These results suggest that, even in a benzene solution, a series of ionic reactions is partly responsible for the formation of the scintillating state of p-terphenyl, and that the apparent quenching effect of ion scavengers is mainly due to their interference in the formation of the excited state of the benzene which is produced by the recombination reaction between the benzene cation and an electron. It was estimated that more than 30% of the excited state of benzene is formed by the recombination reaction.