A neutrino (predicted by Wolfgang Pauli in 1932 and roughly
meaning "little neutral one" in Italian) is a very small particle. It was not discovered until over
twenty years later in an experiment carried out by Cowan and Reines using the Savannah
River reactor in 1956. They were "needed" in order to conserve quantities called spin and
lepton number in some nuclear equations. Vast numbers of neutrinos were formed in the Big
Bang and they are still out there in the Universe – up to 100 million per cubic metre! They are
still being produced in both the nuclear reactions going on in the stars (including our Sun)
and in man made nuclear reactors.
It has an antiparticle called the
antineutrino.
It is thought to
have almost no or indeed no mass.
It has no charge
It can pass though large
distances of matter. Some 1012 neutrinos produced by the Sun pass through your
body every second without causing you any harm. Neutrinos are so penetrating that they can
travel through the Earth from one side to the other with hardly any loss of energy.
It
moves close to the speed of light
It causes little or no ionisation in its
path
Neutrinos are produced in the decay of a neutron and a positron from the
addition of energy to a proton
Antineutrinos are produced as a result of the decay of a
neutron into a proton and an electron
The equations for the production of a neutrino
and an antineutrino are:
In the
first equation a proton decays to a neutron (n) and electron (e) and a neutrino. This only
happens after the addition of energy.
In the second equation a neutron decays to a
neutron (p) and electron (e) and an anti neutrino.
Neutrinos are detected in huge
tanks thousands of metres below ground level. The vast amount of earth and rock above the
tanks filters out all but the highly penetrating neutrinos.