Light absorption properties of the high quality linear alkylbenzene for the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton multi-purpose underground liquid scintillator detector designed to determine the neutrino mass hierarchy, and measure the neutrino oscillation parameters. The excellent energy resolution and the large fiducial volume anticipated for the JUNO detector offer exciting opportunities for addressing many important topics in neutrino and astro-particle physics. Linear alkylbenzene (LAB) will be used as the solvent for the liquid scintillation system in the central detector of JUNO. The light attenuation lengths of LAB should be comparable to the diameter of the JUNO detector, hence very good optical transparency is required. However, the presence of impurities in the LAB renders an intrinsic limit for the transparency. This work focuses on the study of the effects of organic impurities in the LAB, and their light absorption properties particularly in the wavelength region of 350–450 nm. We have prepared LAB samples and measured their light attenuation lengths. These samples were then analyzed by a gas chromatography–mass spectrometry (GC–MS), and the structure formulas of organic impurities were ascertained. These impurities’ light-absorption properties in the wavelength region of 350–450 nm were theoretically investigated with time-dependent density functional theory (TDDFT). The overall optical transparency of the LAB samples was studied, which would further help us in promoting the LAB preparation technique for the mass production thereof, thus improving the transparency of the high quality LAB samples in the near future.