Results from one thousand days of real-time, directional solar-neutrino data

A data sample of 1040 days from the Kamiokande II detector, consisting of subsamples of 450 days at electron-energy threshold ${\mathit{E}}_{\mathit{e}}$\ensuremath{\ge}9.3 MeV and 590 days at ${\mathit{E}}_{\mathit{e}}$\ensuremath{\ge}7.5 MeV, yields a clear directional correlation of the solar-neutrino-induced electron events with respect to the Sun and a measurement of the differential electron-energy distribution. These provide unequivocal evidence for the production of $^{8}\mathrm{B}$ by fusion in the Sun. The measured flux of $^{8}\mathrm{B}$ solar neutrinos from the two subsamples relative to a prediction of the standard solar model is 0.46\ifmmode\pm\else\textpm\fi{}0.05(stat)\ifmmode\pm\else\textpm\fi{}0.06(syst). The total data sample is tested for short-term time variation; within the statistical error, no significant variation is observed.