Quenching of benzene fluorescence in pulsed proton irradiation: Dependence on proton energy

Dilute solutions of benzene in cyclohexane were irradiated with subnanosecond pulses of protons from a 2 MV accelerator. Changes in the time resolved emission at 285 nm were studied as a function of proton energy. The initial rate of fluorescence decay is energy dependent and always greater than that observed with ultraviolet radiation. As time after irradiation increases, the decay rate approaches the uv value. A model based upon quenching by transient species in the proton track is used to analyze the data. The analysis suggests that the energy dependence of the initial decay rate results from the effect of proton stopping power on the initial quencher concentration.