Aging Research Of The LAB-based Liquid Scintillator In Stainless Steel Container

Jiangmen Underground Neutrino Observatory(JUNO) will use 20 ktons of LAB based liquid scintillator(LAB-LS) to accurately measure the neutrino mass order and mixing parameters. The used LS must have high transparency, high light yield, etc. This paper analyzes the effect of oxygen, temperature and stainless steel material on LS. The LS measurement system has been investigated. And the indoor and outdoor LS aging experiments have been done. The specific contents are as follows:(1)The aging factors and the aging mechanism of LS were studied. Analysis and optimization of relative light yield, attenuation length and absorption spectrum measurement system are as follows:①For improving the fitting accuracy of the full-energy peak, a coincidence detector that consists of a La Br3 crystal was added to the relative light yield measurement system.②Trace Pro was used to simulate the attenuation length measurement system to analyze Rayleigh scattering effects. It was noted that coating of Teflon(blackened) and polished liquid pipe has similar attenuation length, which matches well with the experiment results. That means Rayleigh scattering effects can be ignored.(2)High temperature and room temperature LS aging experiments were aimed to analyze the aging effects of temperature, oxygen, stainless steel material.①LS outdoor aging experiments have been done at 65, 70, 75, 80 degrees centigrade. The light yield of 65 degrees centigrade experiment which used seal airtight tanks were reduced little, but the light yield of 75 degrees centigrade experiment whose LS was exposure to air was reduced 15%~20%. This indicates that the oxygen has a great influence on the light yield under high-temperature. Both 65 and 75 degrees centigrade experiment have a small amount of the increase of absorption spectra. All high-temperature aging experiment can effectively avoid reducing the attenuation length in the nitrogen conditions. Type 304 and 316 stainless steel shows a small difference.②LS indoor aging experiments have been done under 40 degrees centigrade and room temperature. Vant’t Hoff equation was used for time transformation and it has a better agreement with the experimental results. After 192 days aging at 40 degrees centigrade and 307 days aging at 25 degrees centigrade, the attenuation length of LS in type 304 and 316 stainless steel tanks fell by about 10% and 6%. The light yields, the absorption spectra and the concentration of the element Fe are almost the same as those unaged one.The results reveal that with nitrogen pumped into each tank, types 316 and 304 stainless steel have only a minor effect on LS, and both of them can be used as vessels and transportation pipeline material for LAB-based LS. When LS storing under high temperature, oxygen has a heavy effect on the performance of LS, but in the nitrogen conditions, oxygen on their impact can be ignored. LS can be stored in sealing container in room temperature, but the nitrogen removal of dissolved oxygen is more conducive to long-term storage of LS.