Number 3 (Story #1), October 11, 1990 by Phillip F. Schewe and Ben Stein THE SOLAR NEUTRINO PROBLEM PERSISTS .The "standard solar model" predicts that the Homestake neutrino detector, operated for 20 years by Ray Davis in a South Dakota gold mine, should observe an average of 1.8 solar neutrinos per day. Instead Davis' observed rate has consistently been much lower than this. Furthermore, the long-term rate, plotted as a function of time, shows an anticorrelation between neutrino rate and sunspot activity. The "solar neutrino problem" has in recent years been tackled by two other groups, and they too record puzzling results. Over a three year period the Kamiokande II detector in Japan sees a neutrino rate about half that expected by the standard model, roughly equal to Davis' average rate for the same period, but without the time variation seen at Homestake. Unlike Kamiokande and Homestake, which are sensitive only to the relatively high-energy neutrinos released in the beta decay of boron in the sun, the Soviet-American Gallium Experiment (SAGE) in the Caucasus (USSR) is designed to observe the lower-energy neutrinos coming from the more plentiful proton-proton fusion reactions in the sun. In five months of running, SAGE has observed essentially no neutrinos at all, further deepening the mystery. Some theorists believe that one explanation may be that solar neutrinos may be "oscillating" from one neutrino type (electron, muon, tau) to another on their way to the earth and thus evading detection. Meanwhile a fourth detector, Gallex, located in Italy, will soon begin operations. (Physics Today, October 1990.)