“The most tiny quantity of reality ever imagined by a human being” – F. Reines
Neutrinos are tiny, mass-less particles that interact with matter. Neutrinos are one of the fundamental particles that make up the universe and are also one of the least understood. The weakness of the weak force gives neutrinos the property that matter is almost transparent to them. Billions of neutrinos pass through our bodies every second. The sun is the main source for neutrinos, although stars, supernovae and nuclear power plants on earth also produce them. The production of neutrinos is through nuclear fusion and decay processes within the cores of the sun and stars.
The sun produces over two hundred trillion trillion trillion neutrinos every second, and a supernova blast can unleash 1000 times more neutrinos than our sun will produce in its 10-billion year lifetime.
There are three types of neutrinos and four fundamental interactions between the particles. There are strong, electromagnetic, weak and gravitational interactions. The weak interaction allows neutrinos to pass through the earth without any deviation. The neutrino has a unique property; its spin is oriented in the direction opposite to its velocity, which is said to be of left helicity. The anti-neutrino is always of right helicity, which is the same direction as the velocity.
The Discovery
Wolfgang Pauli was the first to propose a solution for the missing energy in nuclear beta decays. He believed it was carried by a neutral particle, which was later named the “neutrino” by Enrico Fermi who received the Nobel Prize in 1938. In 1945 Pauli later received the Nobel Prize for his discovery. In 1951 Fred Reines and Clyde Cowan decided to attempt to detect neutrinos. First they tried to detect neutrinos from nuclear explosions. In 1968 the first experiment to detect neutrinos used a liquid chlorine target deep underground. The reports showed that less than half the expected neutrinos are observed. This is the origin of the “solar neutrino problem.” In 1985 a large water detector is used to search for proton decay. It also detects neutrinos. Today we are still searching for techniques to help us learn more about neutrinos. At the Sudbury Neutrino Observatory, data is taken from a vessel built 6800 feet under ground, that contains 1000 tons of heavy water. Heavy water is chemically the same as regular water, but the two hydrogen atoms are replaced with deuterium atoms which are just isotopes of hydrogen, it has one extra neutron. This detector is designed to detect neutrinos produced by fusion reactions in the sun.
