Pauli postulated the existence of new particle, “Neutrino” as early as in 1930. According to Pauli, an additional particle called a neutrino denoted by ‘ν’ is emitted in process of β-decay.

This particle according to Pauli, carries away an amount of energy equal to difference between the observed energy for a β-particle and maximum energy of continuous beta spectrum. The principle of conservation of energy is thus satisfied.

To satisfy Principle of Conservation of Angular Momentum, Neutrino must be assigned following properties

i) It must have zero charge; because in a β-decay process the charge is conserved without neutrino. Also if Neutrino is charged, it would produce ionization which certainly could have been detected. Zero charge in turn implies negligible magnetic moment.

ii) It must have zero or almost zero mass: the mass-energy balance of β-decay processes shows that neutrino rest mass is negligible.

iii) It must have a spin of ½: This will satisfy Law of Conservation of Angular Momentum in β-decay process. Further Neutrino must be a Fermion, so that nuclear statistical requirements are fulfilled.

iv) A neutrino has an antiparticle called anti-neutrino which has zero rest mass, zero charge and spin-1/2.