Solar Neutrino Experiments

A sensitive way to test our understanding of the interior of the Sun is offered by observing the flux of neutrinos from the Sun. As we noted in our discussion of the proton-proton chain, neutrinos are copiously produced by the Sun.

Unfortunately, neutrinos interact only very weakly with matter. Every second over 100 billion neutrinos from the Sun passes through every square inch of your body and essentially none of them interact. Because neutrinos interact so weakly with matter, detecting them is quite a problem. For example, the first Solar Neutrino Experiment or Ray Davis used 100,000 gallons of cleaning fluid (for the chlorine it contained) to hunt for solar neutrinos. Davis only expected to detect a few neutrinos per day!!

So, before we go on, Why do people try to detect neutrinos at all? What makes neutrinos such useful probes of the interior of the Sun?.

• The photons produced in the core of the Sun interact strongly with matter; they travel less than 1 cm in the core of the Sun before they interact with matter. Because of this, photons must diffuse slowly out of the Sun. Typically, it takes around a million years for the photons to leak out of the Sun.

  A change in the rate of energy production by the Sun will not immediately show up as a large change in the Solar luminosity

• The neutrinos produced in the core of the Sun do not interact strongly with matter at all; they will travel more than 6 parsecs (=2x10**19 cm) before they are likely to interact with matter. The neutrinos freely escape from the Sun and reach the Earth in around 8.3 minutes after they are produced!

  Neutrinos are ideal probes for the current state of the Solar interior.

Solar Neutrino Experiments

• There are currently four Solar neutrino experiments in operation.

• The experiments yield surprising results

• The explanations for the results are tantalizing as they suggest that we may learn something about either the Solar Model or we may be learning something about neutrino physics