Development Of Liquid Scintillator’s Attenuation Length Measuring System And Measurement Of Liquid Scintillator’s Relative Light Yield

Neutrino Physics is one of the most active branches in particle physics, which may lead to new physics beyond the Standard Model of particle physics. Over the past few decades, scientists have found neutrino and measured part of its oscillation parameters. Only two mixing parameters’ values are still unknown.The major goal of JUNO(Jiangmen Underground Neutrino Observatory) is determining neutrino mass hierarchy by precisely measuring the energy spectrum of reactor electron antineutrinos at a distance of 53 km from the reactors. LS(Liquid scintillator) is relatively cheap to product, also can easily be made into any form. Its light output is rather high. That’s why liquid scintillator is suitable for huge size detector. The diameter of JUNO’s detector is about 34.5m. The detector is filled with 20000 tons of liquid scintillator. Because of the detector’s size, the optical performance of liquid scintillator have to be very good, and the radiation level is extremely low.This paper on the background of developing high performance liquid scintillator, major work is to build and debug an automatic attenuation length measurement system. Measuring the relative light yield by using different reflecting films. Simulating the changes of light yield when leakage happens in the central detector.In JUNO, LAB(linear alkyl benzene) is used as solvent, PPO is used as luminescent matter and bis-MSB is used as wavelength shifter. The definition of attenuation length is given based on Lambert-Beer law. We analysed the factors that may affect liquid scintillator’s attenuation length. Because the original measurement system is time-consuming and operated by people, error may be brought to the measuring result. Step motor is introduced to the measuring system to control the liquid level. The software is developed by Lab VIEW, which can do the measuring, data fitting and saving the result automatically without human intervention. PMTs in the measuring system are working under high voltage power, so it takes a long time to wait for the PMTs to be stable. That’s one of the reasons why measuring is time-consuming. Therefore, we improved the image processing algorithm, used semiconductor cooling system to reduce camera’s thermal noise, preliminarily explored replacing PMTs by scientific camera. Experiments show that automatic measurement system can achieve the desired aims, whole measuring process can be done without the guards. When attenuation length is rather short, scientific CMOS camera can replace the PMTs to do the measuring.To improve the efficiency of the fluorescence photon absorption, Cherenkov detector in JUNO will be covered with reflective film. Tyvek reflective film is the most commonly used. In this paper, both Tyvek film and ESR film will be used to measure the relative light yield of liquid scintillator. These two kinds of films have big differences in reflecting spectrum, which leads to a different result of light yield measuring. After that, we diluted DYB liquid scintillator 10 times and 100 times, then measured their relative light yield respectively to simulate the central detector leakage. Result shows that there is no significant difference in light yield between pure LAB and 100 times diluted DYB liquid scintillator.