Who discovered the neutron?
Quick answer
British physicist James Chadwick discovered the neutron in 1932 at the Cavendish Laboratory in Cambridge, England. The neutron is a particle in the atom’s nucleus with no electric charge. Chadwick won the 1935 Nobel Prize in Physics for the discovery.
The missing piece of the atom
By the 1920s, scientists knew atoms had electrons and a nucleus with positive protons. But atoms weighed more than their protons alone could explain. Ernest Rutherford, Chadwick’s mentor, suggested a neutral particle might exist in the nucleus.
How Chadwick found it
Other scientists, including Irène Joliot-Curie and Frédéric Joliot, had noticed mysterious radiation coming from beryllium bombarded with alpha particles. They thought it was gamma rays. Chadwick repeated and extended the experiments and showed in February 1932 that the radiation was actually made of neutral particles with about the same mass as a proton: neutrons.
Protons, neutrons and electrons
| Particle | Charge | Location | Discovered |
|---|---|---|---|
| Electron | −1 | Around the nucleus | 1897, J. J. Thomson |
| Proton | +1 | Nucleus | ~1917–1920, Ernest Rutherford |
| Neutron | 0 | Nucleus | 1932, James Chadwick |
See more in which part of an atom has a negative charge.
Why the neutron mattered
Because neutrons have no charge, they aren’t pushed away by the positive nucleus, so they’re ideal for probing and splitting atoms:
- 1938: Scientists discover nuclear fission by hitting uranium with neutrons.
- 1942: The first nuclear chain reaction is achieved in Chicago.
- Today, neutrons drive nuclear power plants and are used to study materials and make medical isotopes.
Chadwick’s later work
During World War II, Chadwick led the British team working on the Manhattan Project in the United States. He was knighted in 1945.
Neutron stars
When giant stars collapse, they can form neutron stars, objects so dense that a teaspoon of their material would weigh about a billion tonnes. Some massive stars, like Betelgeuse, may end their lives this way.
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