Speaker
Description
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 $(6.98 \pm 0.73) \times 10−13$ g/g, and Th232 upperlimit is $3.7 \times 10−13$ g/g (95% C.L., preliminary). On PMT glass, K40 contamination is $(5.73 \pm 0.79stat. \pm 1.49sys. ) \times 10−8$ g/g and Tl208 event rate is $(3.86 \pm 0.26stat. \pm 0.85sys. ) \times 10−3$ Bq/g, indicating $(2.64 \pm 0.18stat. \pm 0.58sys. ) \times 10−6 g/g$ Th232. The radioactivity of LS will be further suppressed after the distillation system is online. The muon flux is $(3.61 \pm 0.19stat. \pm 0.10sys.) \times 10−10 \mathrm{cm}^{−2}\mathrm{s}^{-1}$ with an average energy of 340 GeV, and its neutron yield is $(3.44 \pm 1.86stat. \pm 0.76syst.) \times 10−4μ−1g−1cm2$. Those results indicates that CJPL is an ideal place for low background experiments. We are making steady progresses on lowering radioactive isotopes of detector materials.
