The results of this experiment have been checked against predictions made by standard solar models and it has been discovered that only one-third of the expected solar neutrino flux has been detected . And it is not just the Homestake experiment that is detecting a shortage of neutrinos.
Neutrinos are subatomic particles produced during nuclear fission and fusion processes.
The Sun produces energy by fusing hydrogen to helium. This may be accomplished in a number of ways but in the Sun, a process known as the proton-proton chain is thought to be primarily responsible for energy generation. Numbers indicate different isotopes. Solutions to the solar neutrino problem are usually classified in one of two categories, astrophysical or physical. Solutions that require a change in the way we think about the Sun are termed astrophysical solutions while solutions that require a change in the way we think about neutrinos are called physical solutions.