Neutrons were discovered by

Neutrons were discovered by the British physicist James Chadwick in 1932 [1]. Working at the Cavendish Laboratory at the University of Cambridge, Chadwick conducted experiments where he bombarded beryllium with alpha particles, observing the emission of a neutral radiation that could eject protons from paraffin wax. He concluded that this radiation consisted of uncharged particles with a mass approximately equal to that of a proton, which he named neutrons. This discovery was pivotal as it explained the existence of isotopes and completed the basic model of the atomic nucleus, which previously only accounted for protons and electrons [2]. For this landmark achievement, Chadwick was awarded the Nobel Prize in Physics in 1935 [1]. While Ernest Rutherford had earlier hypothesized the existence of such a neutral particle, it was Chadwick who provided the definitive experimental proof.

Sources

1. [1] https://www.isis.stfc.ac.uk/Pages/materials-world-historical-development-download.pdf
2. [2] https://www.osti.gov/opennet/manhattan-project-history/Events/1890s-1939/exploring.htm