Scientists have proposed a variety of solutions for the mystery of the missing neutrinos. Solar scientists use what they call the standard solar model to account for the sun's behavior and to calculate the expected neutrino flux. In the latest version of the model, Bahcall and Roger K. Ulrich of the University of California, Los Angeles, start with the assumption that the primordial sun was spherical and had an even distribution of chermical elements. They deduce the abundance of heavy elements from recent observations of the solar surface, but allow the ratio of hydrogen to helium to vary. Trying various initial conditions, they calculate how their model sun evolves.
New knowledge leads to refinements of the model.
But the changes have not been large. For example, the sun may have a different composition, internal temperature or pattern of convection currents than assumed in the standard model. Any of these factors could reduce the expected neutrino flux. Indeed, both the Kamiokande and chlorine detectors are sensitive only to a small portion of the neutrinos produced by the sun. B. The rate of that reaction happens to be particularly sensitive to the suds temperature at its core.