Radioactive Cleanliness Control for the JUNO Experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment designed to determine neutrino mass hierarchy, measure oscillation parameters and investigate solar neutrinos, supernova neutrinos and geoneutrinos, etc. The JUNO central detector (CD) contains 20 ktons of liquid scintillator with an acrylic sphere (35.4m inner diameter). Our baseline requirement of surface dusts from LS related systems is less than $0.1 mg/m^2$ for reactor neutrino analysis. In order to achieve this goal, four methods, including conductivity monitoring, light absorption spectra comparison, suspension particulate counting and ICP-MS measurement, are applied to monitor cleanliness levels. Multiple cleaning protocols are developed and verified to clean surface of acrylic, stainless steel and Teflon. The poster presents details of evaluation methods and cleaning protocols. The total signals rate contribution from surface cleanliness is less than 0.32 Hz in the fiducial volume (17.2m radius).