2.1 Theory
One of the radioactive decays, which were discovered by Bequerel (1896) and
investigated by Curie (1898), is the so-called (Thomson in 1899) b -decay.
At first it was observed on the heaviest natural isotopes with an excess of
neutrons. The ' b -particle' was found to be an electron emitted by the
nucleus inside which a neutron transformed into a proton. Because of
unexplainable discrepancies regarding conservation laws and the
Pauli-principle, Pauli in 1930 proposed the (probably massless) neutrino. This
b -decay then could be regarded as the interaction of four fermions, which
theoretically was first described by Fermi [Fer34].