The Influence of Oxygen on Pulse Shape Discrimination at Various Solvents and Phosphors

In this work, the issue of oxygen quenching on the pulse shape discrimination (PSD) ability/quality of liquid scintillation cocktails is addressed throughout the investigation of the effect of different solvents on PSD quality and light yield using different concentrations of the phosphor PPO + MSB. Two different atmospheric conditions were in the preparation of the samples, one consisted of air at standard temperature and pressure (STP) and the other was nitrogen. The second part of the work is focused on the influence of the phosphors on the PSD quality and light yield. The effect of only one phosphor with a large Stokes shift was investigated, as well as the effect of a secondary phosphor as a wavelength shifter within the used solvents, again prepared under a nitrogen atmosphere and ambient environment. The used solvents can be divided into three categories: 1) classical (toluene, xylene, and styrene); 2) naphthalene derivatives (di-isopropyl naphthalene (mixture of isomers) and 1-Methylnaphthalene); and 3) linear alkylbenzenes (Diethylbenzene, Dodecylbenzene, and Propylbenzene). Five phosphor groups were tested using different phosphors or mixtures of phosphors namely para-terphenyl and 1,4-bis(5-phenyloxazol-2-yl) benzene (pTP + POPOP), 2,5-Diphenyloxazole and p-Bis(o-methyl-styryl) benzene (PPO + MSB), 1-Phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline (PYR), 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene (THIO), and 2-(1-naphthyl)-5-phenyloxazole (NPO). The first one is the oldest one with very good PSD ability, and the second one is standard in PSD scintillators. The rest of them are experimental phosphors with large Stokes shifts without the need for a second phosphor (wavelength shifter).