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
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
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
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
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
The interaction between neutrinos and the fluid used in the detectors
may be different than expected.
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