Study on acrylic transmittance for JUNO Central Detector

The Central Detector (CD) of the Jiangmen Underground Neutrino Observatory (JUNO) uses 20,000 tons of liquid scintillator as target mass, and the design value of energy resolution of neutrino is 3% at 1 meV. Acrylic transmittance is an important parameter for CD in order to maximize the detection of scintillating photons. The composition and processing techniques of acrylic can surely affect its transmittance. How the composition, thermoforming temperature, heat preservation time and surface treatment process of acrylic affect its transmittance was measured and analyzed. According to these studies, JUNO determined its special acrylic composition and processing techniques: no components of plasticizer or anti-UV in the composition, decreasing the time span and temperature during the demolding of flat panel, and adopting suitable thermoforming temperature of spherical panel. Finally, the preproduction of spherical acrylic panels meets the JUNO requirement confirming a transmittance in ultrapure water greater than 96% at the wavelength of 420 nm.