ABSTRACT
The work of Gribov and Pontecorvo was extended by Wolfenstein. He noted the interest in the question of neutrino oscillations and specified conditions under which such oscillations could occur. One result of Wolfenstein s calculation, for conditions he regarded as unlikely, was that neutrino oscillation would cause a reduction in the number of solar neutrinos but that the reduction was not large enough to solve the solar neutrino problem. Super-Kamiokonde, a water-Cerenkov detector approximately ten times larger than Kamiokonde, began operations and the first results on atmospheric neutrinos appeared in 1998. The larger detector acquired data much more rapidly and provided better evidence in support of neutrino oscillations. The failure of the solar neutrino experiments to obtain results in agreement with the Standard Solar Model led to questions concerning that model and to questions concerning other possible properties of the neutrino, such as neutrino decay and neutrino oscillation.
