Spark image

The Neutrino

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.

Properties of neutrinos and antineutrinos

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:

Neutrino production:      p decays to n + e+ + neutrino
Antineutrino production:     n decays to p + e- + antineutrino

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.

© Keith Gibbs 2011