The mean free path of a neutrino in water would be on the order of 10x the distance from the Earth to the Sun. In the standard Big Bang model , the neutrinos left over from the creation of the universe are the most abundant particles in the universe. The sun emits vast numbers of neutrinos which can pass through the earth with little or no interaction. Kearns et al. put the flux of neutrinos at the Earth's surface at 60 billion per second per square centimeter. A remarkable opportunity for observing neutrinos came with Supernova 1987A when the Japanese observing team detected neutrinos almost coincident with the discovery of the light from the supernova.
Neutrinos interact only by the weak interaction .
Their interactions are usually represented in terms of Feynman diagrams . Index References Kearns, et al. The first direct observation of the neutrino interacting with matter was made by Frederick Reines, Clyde Cowan, Jr, and collaborators in 1956 at the Savannah River Plant in South Carolina. Modern neutrino detectors at IMB in Ohio and Kamiokande in Japan detected neutrinos from Supernova 1987A . A new neutrino detector at Sudbury , Ontario began collecting data in October of 1999.