The study of radioactive disintegrations indicates the emission of alpha, beta and gamma particles/rays to be of nuclear origin. Further, study of artificial radioactivity has revealed that many other particles like proton, neutron, alpha particles, beta particles and sub-particles like meson, positron, neutrino enter into the constitution of the nucleus in one way or the other.
Several hypothesis have been put forward about the structure of the atomic nucleus. Prominent among them are:
1. Proton-electron hypothesis
2. Proton-neutron hypothesis