James Chadwick, in 1932, discovered the neutron through the following experimental setup. This setup had been previously used by other scientists, namely Frederic Joliot and Irene Joliot-Curie, to demonstrate that an unidentifiable source of energy was being produced.
1. Using an alpha particle source, namely polonium, he bombarded beryllium. The radiation which was emitted from the beryllium was aimed toward a piece of paraffin.
2. The paraffin, in turn, was shown to emit protons as a result of the bombardment of this unknown radiation. The protons were detected using a Geiger counter. Both of these steps were already performed by the Joliot-Curies.
3. Chadwick measured the energies of both the radiation emitted by the beryllium and the energies of the protons emitted from the paraffin.
Chadwick was able to demonstrate from his calculations that the unknown radiation had tremendous penetrating power due to its neutral charge. However, unlike gamma radiation which is also neutral, Chadwick was able to show that the radiation from the beryllium had a mass. The mass of the particle was around the same mass as the proton. Chadwick had discovered the neutron.
