Neutrino

The neutrino is an elementary particle.

There are three known types (flavours) of neutrino: electron neutrino, muon neutrino and tau neutrino;

Because the cross section in weak nuclear interactions is very small, neutrinos can pass through matter almost unhindered. For typical neutrinos produced in the sun (energy of a few MeV), it would take approximately one light year (~1016m) of lead to block half of them. Detection of neutrinos can therefore be challenging, requiring large detection volumes or high intensity man-made neutrino beams.