Liquid Scintillator Development for the SABRE Detector Experiment

The SABRE (Sodium-iodide with Active Background REjection) experiment consists of 50 kg of ultrapure NaI(Tl) scintillators contained within a 10.5 tons liquid scintillator (LS) veto detector, and will search for dark matter interactions in the inner NaI(Tl) detector. SABRE will be housed in a new Australian underground laboratory at Stawell, Victoria. Linear Alkyl Benzene (LAB) will be used as the LS solvent, together with PPO (2,5-Diphenyloxazole) and Bis-MSB (4-Bis (2-methylstyryl) benzene) as primary and secondary fluorophores, in the SABRE veto detector. The SABRE physics goals require LAB of high chemical purity to maximise the light yield and optical attenuation length of the veto detector's scintillator. This study focuses on analysis of LAB samples purified using vacuum distillation and a LAB sample prepared separately though column purification. The analysis includes attenuation length measurement with UV-Vis spectroscopy, the identification of organic impurities using the gas chromatography-mass spectrometry (GC-MS) and light yield measurements. The UV-Vis and GC-MS results for LAB samples confirmed that recursive distillation reduced the organic impurities in the wavelength region 330 to 500 nm. The chemical identity of three organic impurities were determined tentatively with GC-MS. The purification of LAB improved the scintillation light yield by as much as 13%, compared to scintillator that used unpurified LAB. In conclusion, the study provides very useful information in regard to LAB purification, light yield, and optical transparency improvement both for the SABRE and future research experiments in the area of particle physics and nuclear science.