Beta decay

 Beta decay;

Beta decay is a spontaneous radioactive decay process in which either a neutron gets converted into proton or a proton gets converted into neutron with the emission of electron or positron respectively.

Whenever proton or neutron are in higher energy level because they are in excess they get converted into another kind of particle and thus decreasing the energy of the system and increasing its stability.

In ¹²B there are seven neutrons and five protons while in ¹²C there are six neutrons and six protons, since both protons and neutrons are fermions and no more than two same kind of fermions can occupy the given energy level. Thus the figure below shows the nuclear energy diagram of ¹²C and ¹²B.

Since in ¹²B nucleus, there are two neutrons present in excess, if a neutron gets converted in proton, then this new proton occupies an energy level lesser in energy than that of neutron and thus giving a stable ¹²C nucleus.

Pauli theory of beta decay;

An interesting historical development is associated with beta decay process which lead to the prediction of new fundamental particle known as neutrino. Thus is known as neutrino hypothesis.

The beta decay process violates the following conservation laws

1) Conservation of energy

The kinetic energy of electrons emitted is less than the kinetic energy predicted or expected.

2) Conservation of linear momentum 

The electron emitted and the recoiling daughter nuclei are not exactly in the opposite direction, which must be in order to conserve linear momentum.

3) Conservation of spin

The particle involve in beta decay process i.e protons, neutrons and electrons are fermions i.e they have 1/2 spin. The spin is not conserved in beta decay process.

But charge is conserved in beta decay process.

Wolfgang Pauli and later Enrico Fermi have suggested that an uncharged, light, half spin particle must be emitted with the electron in beta decay process in order to prevent the violation of these laws.

This particle was named neutrino which means 'little neutral ones' which was discovered experimentally later and thus validating neutrino hypothesis.

Neutrino is denoted by 𝜈. Some distinction in neutrino was observed on the basis of their spin and angular momentum. Neutrino are the particles which have spin vector parallel to its angular momentum vector while antineutrino are the particles which have spin vector opposite to its angular momentum vector.