Question

How was neutron discovered?

Answer 1

• James Chadwick, a scientist, conducted an experiment in which he hit Beryllium with alpha particles produced by Polonium's natural radioactive disintegration in 1932.
• The radiation that resulted had a high penetration through a lead shield, which could not be explained by the particles available at the time.
• The following chemical reaction was observed:

${}_{}{}^9\mathrm{Be}+{}_{}{}^4\mathrm{He}\left(\mathrm{\alpha }\right)\to {}_{}{}^{12}\mathrm{C}+{}_{}{}^1\mathrm{n}$

• To prove that the discovered particle was a neutron, he measured mass of the particle using the velocity of the expelled protons and came to the conclusion that the mass of neutrons was 1.0067 times mass of a proton.