First Study of Neutron Tagging with a Water Cherenkov Detector

Abstract A first study of neutron tagging is conducted in Super-Kamiokande, a 50,000 ton water Cherenkov detector. The tagging efficiencies of thermal neutrons are evaluated in a 0.2% GdCl 3 -water solution and pure water. They are determined to be, respectively, 66.7% for events above 3 MeV and 20% with corresponding background probabilities of 2 × 10 - 4 and 3 × 10 - 2 . This newly developed technique may enable water Cherenkov detectorsto identify ν ¯ e ’s from astrophysical sources as well as those produced by commercial reactors via the delayed coincidence scheme.