In 1932, James Chadwick became the first person to discover neutrons. Chadwick had experience working with Rutherford, who discovered protons.
After the discovery of protons, scientists found that protons were not the only particle in the nucleus. The number of protons in the nucleus is called atomic number. It is equal to the positive charge of the atom. During atomic disintegration, scientists were baffled to find that atomic number was less than atomic mass. For example, a helium atom’s mass is four whereas its atomic number is just two.
Because electrons have almost no mass, scientists assumed that something other than protons were adding to the mass. Chadwick kept this problem in mind even while he was engaged in other matters. He conducted many experiments to find a neutral particle with zero charge that has the same mass as a proton. Finally, Chadwick proved the existence of neutrons and determined that its mass was about 0.1 per cent more than the proton’s. In a characteristic display of modesty, he published his findings in a paper titled Possible Existence of a Neutron. Chadwick was awarded the Nobel Prize in 1935 for his discovery.
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