Discovery of Neutron
A neutron is a neutral particle carrying no charge, and having mass equal roughly to the mass of a proton. This particle was discovered experimentally by Chadwick in the year 1932:
(i) Chadwick observed that when beryllium was bombarded with alpha particles, some neutral radiations were emitted, which could knock out protons from light nuclei like helium, carbon and nitrogen.
(ii) Applications of the principles of conservation of energy and momentum showed that neutral radiations from bombardment of beryllium could not be photons. Chadwick solved by assuming that these neutral radiations consisted of hitherto unknown neutral particles-which were called neutrons.
Chadwick estimated the mass of a neutron being roughly equal to mass of a proton.
Whereas a free proton is stable; a free neutron is unstable and has a mean life of 1000 second. Neutron is however, stable inside the nucleus.
Chadwick was awarded the 1935 Nobel Prize in Physics for his discovery of neutron.