James Chadwick and the Discovery of the Neutron

James Chadwick
(1891 – 1974)

On February 27, 1932, English physicist and Nobel Laureate Sir James Chadwick published an article in the scienticic journal ‘Nature’ about the discovery of the neutron, a previously unknown particle in the atomic nucleus.

James Chadwick was born and raised in Bollington, England and later studied at Manchester and Cambridge University. Just before the start of World War I, Chadwick moved to Berlin, studying at the city’s Technical University under Ernest Rutherford and Hans Geiger. During the war, Chadwick was detained to the ‘Ruhleben internment camp’ near Berlin, where he was allowed to put up a little laboratory. In these years he worked on the ionization of phosphorus and on the reaction of chlorine and carbon monoxide.

Returned to Cambridge, James Chadwick discovered an until then missing piece in the atomic nucleus in 1932, which was later known as the neutron. The search for the particle began around 1920, when Ernest Rutherford published his ideas on its possible existence. In his understanding, the neutron was to be a neutral double consisting of an electron that orbited a proton. About a decade later, Viktor and Dmitri Ivaneko however proved that the nucleus could never consist of protons and electrons and in the following year, German scientists found out that in case of alpha particles being emitted from polonium and falling on beryllium, boron or lithium, radiation was produced, which they took for gamma rays. Iréne Joliot-Curie (daughter of Marie Curie) and Frédéric Joliot proved that the previously discovered radiation ejected protons of high energy, when falling on a hydrogen containing compound.

The next person known to have been experimenting on the gamma ray theory was James Chadwick himself. He performed many experiments, stating that the radiation his German colleagues talked about contained uncharged particles of about the mass of a proton. The particles were called neutrons and his theory spread quickly, earning a great reputation amongst other scientists all over the world.

Chadwick’s discovery was critical in the sense of general physics and especially in concerns of nuclear fission. The Italian scientist Enrico Fermi was through Chadwick’s achievements motivated to investigate various nuclear reactions which led to Otto Hahn and Fritz Strassman discovering the first nuclear fission…but this is already another story. Chadwick became aware of the possibility building a nuclear bomb and joined the ‘Manhattan Project’ .

James Chadwick passed away on July 24, 1974 in Cambridge.

At yovisto, you may enjoy a short video lecture by Tyler DeWitt on the ‘Atomic Structure: Discovery of the Neutron

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