PURIFICATION AND CHARACTERIZATION OF THE JUNO LIQUID SCINTILLATOR: FIRST RADIOPURITY RESULTS

My PhD work has been carried out within the JUNO experiment, a large liquid scintil- lator experiment devoted to study neutrinos. JUNO (Jiangmen Underground Neutrino Observatory) is the largest organic liquid scintillator detector ever built. It exploits 20000 tons of organic liquid scintillator contained in a huge Acrylic Vessel (d = 35 m), detecting neutrinos and anti-neutrinos from natural sources and Nuclear Power Plants. The experiment construction was completed in December 2024 and, after a filling phase which lasted more than 9 months, data-taking started on August 26th 2025. The main goal of JUNO is to determine the Neutrino Mass Ordering (NMO) detecting reactor anti- neutrinos. Thanks to its very large mass, low backgrounds and unprecedented energy resolution JUNO will be also a powerful detector for solar neutrinos, produced by nuclear reactions burning in the core of the Sun. Radioactivity is a problem for the NMO analysis and even more for solar neutrino flux measurement. For this reason, the scintillator purification strategy plays a key role in the preparation of the experiment. My PhD work has covered several crucial aspects of the JUNO project: before the begin- nig of the JUNO operations, I have performed a Monte Carlo based study to determine the JUNO sensitivity to 7Be, pep and CNO solar neutrinos. On the hardware side, my activity has been devoted to the purification of the JUNO liquid scintillator (commis- sioning and operation of the distillation and stripping plants during filling) and to the characterization of its optical properties (on small laboratory scale with the SHELDON facility). During filling I have studied and monitored the radio purity of the scintillator produced by the purification plants performing the analysis of the first data collected by the JUNO detector and by the ancillary detector OSIRIS. After the beginning of the official JUNO data-taking with the full detector on August 26th, I have performed the analysis of the first two months of data to study the detector response (analyzing the calibration data) and the radioactive backgrounds. I have also started working at the solar neutrino analysis, performing a sensitivity study using Monte Carlo data devoted to 7Be, pep and CNO solar neutrinos.