Chadwick was born in 1891 in Manchester, England. He was graduated from Manchester University in 1911 and remained to work with Ernest Rutherford. In 1913, he received a scholarship to study in German, placing him in Germany at the beginning of World War I. After Chadwick was detained as a civilian prisoner of war, he returned to England in 1919 to carry out research at Cambridge University. In 1923, he became the assistant director of research at the Cavendish Laboratory.

Rutherford discovered that atoms have minute and dense nuclei, with the nucleus holding a positive charge in the charge of a hydrogen nucleus. Physicists wanted to determine where the extra mass was living. Chadwick helped answer this question when identifying the neutron (particle without an electric charge in the nucleus) in 1932. Chadwick had created an experiment to answer the question of this unknown nucleus mass source.

Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed the radiation that was released to hit another target: paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. In physics it is known that only a particle having almost the same mass as a hydrogen atom could effect hydrogen in that manner. The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named neutrons. This provided the answer for hidden mass in atoms.

Chadwick's discovery advanced experimental work for all scientists. Since neutrons have no electrical charge, any neutrons fired from a source has the ability to go through deep layers of materials and to go into the nuclei of the target atoms. After Chadwick's work, scientists world-wide began bombardment of all types of materials with neutrons. It was discovered that when uranium is a target, nuclear fission becomes possible, resulting in nuclear weapons and nuclear power plants.
 

 
In 1935, Chadwick received the Nobel Prize for Physics for this discovery. During World War II, he worked with the British atomic bomb project, and was a science advisor to Oppenheimer on the Manhattan Project. The Manhattan Project was the first time an atomic bomb had been produced. Chadwick was knighted in 1945, and died in 1974 at Cambridge.

Sources:

1. Brown, Andrew P. The Neutron and the Bomb: A Biography of Sir James Chadwick. Oxford University Press: NY 1997

2. Snow, C. P. The Physicists. Little & Brown: Boston, MA. 1981

Further Study:

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