In nature, the nuclei of many basic substances break down spontaneously. All these nuclei are called radioactive nuclei. Alpha , beta and gamma rays are emitted from these nuclei. When a beta particle is emitted from a radioactive nucleus, energy is emitted at the same time. However , the amount of energy emitted from the nucleus is greater than the kinetic energy of a beta particle . In 1930, W. Pauli proposed that the remaining energy is carried by another type of particle which is emitted along with the beta particle , this particle is called neutrino. Due to which the process of rupture of many nuclei occurs