Background measurements at Jinping Neutrino 1-t prototype

In 2017-2020, Jinping Neutrino 1-t prototype has detected numerous MeV radioactive background events, 343 high energy muon events and muon induced neutrons. By Bi-Po coincidence, the U238 contamination of liquid scintillator (LS) is measured as (6.98 ± 0.73) × 10^{-13} g/g, and Th232 upperlimit is 3.7 × 10^{-13} g/g (95% C.L., preliminary). On PMT glass, K40 contamination is  (5.73 ± 0.79stat. ± 1.49sys. ) × 10^{-8} g/g and Tl208 event rate is (3.86 ± 0.26stat. ± 0.85sys. ) × 10^{-3} Bq/g, indicating (2.64 ± 0.18stat. ± 0.58sys. ) × 10^{-6} g/g Th232. The radioactivity of LS will be further suppressed after the distillation system is online. The muon flux is (3.61 ± 0.19stat. ± 0.10sys.) × 10^{-10}cm−2s−1 with an average energy of 340 GeV, and its neutron yield is (3.44 ± 1.86stat. ± 0.76syst.) × 10^{-4}μ−1g−1cm2. Those results indicates that CJPL is an ideal place for low background experiments(for LRT)/neutrino experiments(for Neutrino). We are making steady progresses on lowering radioactive isotopes of detector materials.