It is a remarkable fact the existence of neutron was not discovered until 1932. The general atomic imagination of the time was protons and electrons. Through Rutherford’s alpha scattering experiments, it was found out that the Atomic mass number A of an element is a bit more than twice the atomic number Z for most atoms and that essentially all the mass of an atom was concentrated in a very tiny space at the center of the atom. The alpha particles that took a 180-degree turn stand as a proof to this.
Discovery of Neutron, Isotopes, Isobars and Isotones
Until 1930, a few electrons were thought to coexist with the protons in the dense nucleus but the immense amount of energy required to sustain such a system was way beyond the atomic energies. If we take the size of a Hydrogen atom as 0.2 nano meters, then the electron confinement energy is 38eV which is the correct magnitude for atomic electrons. But if the electron were to coexist with the protons in the nucleus, the electron confinement energy is approximately 250Mev! Many magnitudes huger than the 38eV.
Who discovered the Neutron?
A breakthrough came when it was shown that the bombardment of Beryllium with alpha particles from a radioactive source yielded penetrating but non-ionizing radiation. Such a neutral radiation confounded the scientists since the only known neutral radiation than were photos. The neutral radiation had it been a photon would exit the beryllium atom with far more energy than it actually does.