Neutrons were first discovered in 1932 by James Chadwick. Chadwick conducted research with Ernest Rutherford who discovered the proton.
While conducting research at Cambridge University, James Chadwick worked with Ernest Rutherford. Rutherford engrained his name in history when he discovered the proton. With more research, he — as well as other researchers — determined that it was not the only particle that made up the nucleus.
Rutherford hired Chadwick in 1921, where he focused his research on radioactivity. At this time, the duo focused on studying atomic disintegration. In their research, they found that the atomic number was always less than the atomic mass. There were several explanations that tried to clarify it, but none of them were backed with evidence.
Rutherford was the first one to classify a neutron. However, it was Chadwick that finally found the evidence to prove that it existed. He used similar experiments as some French researchers who were reviewing particle radiation. However, he turned the study on its side by focusing on finding the neutral particle. It was at this time that he formally discovered the neutron.
In 1935, Chadwick was awarded the Nobel Prize for his discovery. After that, he changed the face of atomic research. Researchers such as Werner Heisenberg showed that it wasn't a pairing of an electron and a proton like initially thought but that it was its own particle that existed within the atom.