(i) Weak Nuclear forces were discovered during the study of the phenomenon of ß-decay, in radioactivity.
(ii) In ß-decay, electrons are emitted from a radioactive nucleus. It was believed that ß-decay occurs when a neutron in the nucleus is converted into a proton and an electron. According to theoretical considerations, all ß- particles from a radioactive nucleus should possess the same energy and hence same velocity.
(iii) Experiments, however, show that the energy of electrons emitted from a radioactive nucleus varies continuously from zero to a certain maximum value.
(iv) To account for the variable ß–ray energy, Pauli in 1930, postulated the existence of an uncharged particle, called antineutrino which is emitted along with the ß-particle.
(v) The energy emitted during ß-decay is shared by ß-particle and antineutrino. When antineutrino carries maximum energy, the energy of particle is minimum and vice-versa. This particle was later discovered experimentally.
Hence it was concluded that an electron and an antineutrino interact with each other through weak forces. Thus the weak forces are the forces of interaction between elementary particles of short life times.
Properties of Weak Nuclear Force
1. The weak forces are 1025 times stronger than the gravitational forces.
2. The weak Nuclear forces exist between leptons and leptons: mesons and mesons etc. (Note: – Leptons and mesons are kinds of elementary particles.)
Other properties of Weak Nuclear Forces are yet under investigation.