Preparation of Gd Loaded Liquid Scintillator for Daya Bay Neutrino Experiment

Gadolinium loaded liquid scintillator (Gd‐LS) is an excellent target material for reactor antineutrino experiments. Ideal Gd‐LS should have long attenuation length, high light yield, long term stability, low toxicity, and should be compatible with the material used to build the detector. We have developed a new Gd‐LS recipe in which carboxylic acid 3,5,5‐trimethylhexanoic acid is used as the complexing ligand to gadolinium, 2,5‐diphenyloxazole (PPO) and 1,4‐bis[2‐methylstyryl]benzene (bis‐MSB) are used as primary fluor and wavelength shifter, respectively. The scintillator base is linear alkyl benzene (LAB). Eight hundred liters of Gd‐LS has been synthesized and tested in a prototype detector. Results show that the Gd‐LS has high quality and is suitable for underground experiments in large quantity. Large scale production facility has been built. A full batch production of 4 t Gd‐LS has been produced and monitored for several months. The production of 180 t Gd‐LS will be carried out in the near future.