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Neutrinos produced in the Sun have different energies. Different types of detectors are sensitive to different energy ranges.
Image courtesy of John Bahcall, Institute of Advanced Studies

The Solar Neutrino Problem

Theories about fusion inside the solar core predict the number of neutrinos that should reach Earth. Experiments on Earth have been set up to detect solar neutrinos in order to test the validity of these models. Current measurements yield a neutrino flux that is smaller than the theoretical prediction.

The first solar neutrino experiment was performed at the Homestake mine in South Dakota. A 600 ton chlorine fluid detector was used and found a neutrino count about one third of the theoretical prediction.

The experiment at Kamioka, Japan, found about half of the predicted neutrino flux. Recent experiments in Russia (SAGE) and Italy (GALLEX) use Gallium to detect neutrinos and have found neutrino fluxes up to 70% of the predicted flux.

Hypothesis that have been formulated to explain the differences between measurements and theory include the following:

  • Models of the solar core may need to be refined to improve the prediction of the neutrino energy spectrum. (Neutrinos produced in the Sun have different energies and the detectors are sensitive to specific energy ranges).
  • There are different types of neutrinos (electron-, muon-, and tau-neutrinos). Electron neutrinos can be transformed into muon- and tau-neutrinos, which would not be detected by many of the present-day experiments. A detector that is sensitive to all types of neutrinos is presently under construction in Canada (SNO, Solar neutrino Observatory).
  • The interaction between neutrinos and the fluid used in the detectors may be different than expected.

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