Precise measurement of attenuation length of the JUNO liquid scintillator

Introduction The Jiangmen Underground Neutrino Observatory has critical requirements on quality of the liquid scintillator, one of which is long attenuation length. Purpose A system with a height of 3 m is used to precisely measure the attenuation length of the liquid scintillators. Methods The light generated by a LED is transmitted through an optical fiber. After being focused, filtered and collimated, the light enters the test tube with the liquid scintillator and is detected by the PMT. The stepping motor is controlled by the Labview program to adjust the level of the liquid scintillator, and the emitted light intensity of different liquid levels can be obtained to fit the attenuation length. In addition, the systematic errors have been studied, which includes the measurement error of the emitted light intensity and the error caused by the movement of light spot, and the latter is responded to the non-uniformity of the PMT photocathode. Meanwhile, analytical methods were improved. Results The system can measure the attenuation length stably and a small error was obtained, including statistical error and systematic error (0.69–23.70 m).