Measurement Of LS Solvent's Light Absorption And The Research Of Impurity Effects

Neutrino is an elementary particle that is able to pass through ordinary matter almost unaffected. This makes neutrinos extremely difficult to detect. Therefore, neu-trino detectors must be very large in order to detect a significant number of neutrinos. Recently, many large-scale liquid scintillator detectors were constructed in reactor neu-trino oscillation experiments, solar neutrino experiments, geo-neutrino experiments and so on. These neutrino detectors are usually constructed by liquid scintillator sol-vent (LS solvent), liquid scintillator (LS), and PMT system. In order to achieve a high precision result of the neutrino experiments, stringent requirements were set to control the quality of the materials used in detector construction. The first and most important requirement for LS solvent is good light transparency properties (long light attenua-tion length, at the magnitude of meter). So, it is of great importance to analyze the constitution of the impurities in LS solvent and the influences of these impurities.Linear alkyl benzene(LAB) is a typical liquid scintillator solvent. Recently, it is newly used in large-scale neutrino detectors. more than hundreds or thousands tons of LAB are used in the construction of the neutrino detectors of SNO+, Reno, Daya Bay, Double chooz (veto detector) and other neutrino experiments. As a mixture sol-vent, the industrial produced LAB may contain a lot of impurities. In this thesis, we used GC-MS and GC×GC-MS to analyze the impurities of LAB samples collected from Nanjing LAB plant. Two different types of potential impurities were detected in the LAB samples, whose light attenuation length was not satisfied the experimental requirement. These two types of impurity compounds may influence the ligth trans-parency of the LAB samples. Detailed, these two types impurities are belong to thiocarbonyls and nitroben-zene derivatives. In order to investigate the detail light absorption properties of these two types compounds, we used the popular TD-DFT method to calculation the wave-length and oscillator strengths of these compounds'absorption maximum. TD-DFT can quickly get the acceptable results of the small-size organic compounds' excitation properties with medium time cost. The calculation results showed that some com-pounds of the two types can have absorption peaks in the characteristic wavelength re-gion 350-550 nm. The thiocarbonyl impurities were found to have only weak intensity absorption in our characteristic wavelength region, while the nitrobenzene derivatives were found to have intense light absorption in 350-550 nm. Thus, even tiny concentra-tion of this type compound could greatly decrease the light attenuation length and weak the light transparency of LAB samples. These impurities should be removed before LS solvent used in neutrino experiment.At the end of this thesis, we also introduced some methods to improve the light quality of LAB samples. These methods are purification with activated alumina oxide powders and silica gel powders, oxygen quenching and industrial process control.