Nonlinear Responses of Poly(vinyl toluene) Plastic Scintillators at High Excitation Doses

The light output intensities from commercial Pilot B and similar plastic scintillators having a poly(vinyl toluene) host were measured as a function of dose from a pulsed electron beam machine. At doses exceeding ∼ 1.5 × 104 rad in 3 × 10−9 sec, nonlinear responses were observed. For pure poly(vinyl toluene) the nonlinear responses can be explained by bimolecular interaction of the host excited states, and the product of the excited-state yield times the interaction rate constant is 8.5 × 10−10 cm3 sec−1 per 100 eV. For Pilot B it is concluded that the dominant quenching mechanism is the reabsorption of scintillator light by mononegative ions of th e center fluor, p-terphenyl. This conclusion is corroborated by the observation of the spectrum of decreased light transmission through the sample after electron excitation at high doses. The observed product of ion yield times extinction coefficient is 2.3 × 105 liter mole−1·cm−1 per 100 eV.