Number 3, 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.) THE COMPACT IGNITION TOKAMAK ,the proposed next-generation fusion machine, would be the first device in which fusion reactions would become self-sustaining. The CIT plan, put forward by the Princeton Plasma Physics Laboratory (where earlier this year their TFTR tokamak achieved a record-high plasma temperature of 348 million K) would, if approved by the Department of Energy and by Congress, cost an estimated billion dollars and would be under construction over the period 1992-1998. But even this represents only the next of several steps. An even bigger demonstration machine, perhaps engaging international cooperation, will be needed before a practical commercial-power-generating plant using fusion reactions could be built. Some experts believe that such a plant might be feasible by the year 2040. (The New York Times, October 9, 1990; part of an occasional series of articles on "big-versus-small science.") INHIBITION OF SPONTANEOUS EMISSION: Scientists at Brown University have succeeded in at least partly inhibiting spontaneous emission of laser-excited dye molecules by embedding them in an array of polystyrene spheres suspended in water. The spheres are transparent to radiation at some wavelengths and opaque at others, particularly in certain directions as defined by the geometry of the polystyrene array. By studying the inhibition of spontaneous emission, scientists hope to make lasers more efficient and hope to learn more about various quantum-electrodynamic effects. (Physical Review Letters, October 8, 1990; contact Nabil M. Lawandy at Brown University, 401-863-2755.)