Evaluation of p-terphenyl and 2,2″ dimethyl-p-terphenyl as wavelength shifters for barium fluoride

Abstract

p-Terphenyl (PTP) and 2,2″ dimethyl-p-terphenyl (DMT) have been investigated for use as wavelength shifters (WLSs) for barium fluoride (BaF 2) scintillation emission. These two organic fluors are attractive due to their high quantum efficiency, fast fluorescence decay time, and emissions above the wavelength cut-off of borosilicate glass. Measurements of these WLSs dissolved in cyclohexane are presented. Coincidence time spectra and fluorescence decay spectra measured with BaF 2 as the pump source, are shown. The fluorescence decay time and the ratio of fast to slow intensities were determined from the fluorescence decay spectrum. The increase in signal resulting from using a WLS between the borosilicate end-window photomultiplier tube and the BaF 2 crystal is measured. The motivation behind this work is the development of a gamma-ray spectrometer suitable for high count rate applications. We are also investigating the possibility of separating the fast and slow emissions of BaF 2 using optical techniques. PTP and DMT both can spectrally separate BaFe 2 emissions to a marginal extent.