James Chadwick

Sir James Chadwick, CH, FRS (20 October 1891 – 24 July 1974) was an English nuclear physicist who was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932. During WW II, Chadwick headed the British team that worked on the Manhattan Project. In 1945, George VI of the United Kingdom appointed him Knight Bachelor.

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Quotes

It has been shown by Bothe and others that beryllium when bombarded by α-particles of polonium emits a radiation of great penetrating power, which has an absorption coefficient in lead of about 0.3 (cm.)^–1. Recently Mme. Curie-Joliot and M. Joliot found, when measuring the ionisation produced by this beryllium radiation in a vessel with a thin window, that the ionisation increased when matter containing hydrogen was placed in front of the window. The effect appeared to be due to the ejection of protons with velocities up to a maximum of nearly 3 × 10⁹ cm. per sec. They suggested that the transference of energy to the proton was by a process similar to the Compton effect, and estimated that the beryllium radiation had a quantum energy of 50 × 10⁶ electron volts.
- (1932). "Possible existence of a neutron". Nature 129 (3252). DOI:10.1038/129312a0.

The idea that there might exist small particles with no electrical charge has been put forward several times. Nernst, for example, suggested that a neutral particle might be formed by a negative electron and an equal positive charge, and that these "neutrons" might possess many of the properties of the ether; while Bragg at one time suggested that the γ-rays emitted by radioactive substances consisted of small neutral particles, which, on breaking up, released a negative electron.
The first suggestion of a neutral particle with the properties of the neutron we now know, was made by Rutherford in 1920. He thought that a proton and an electron might unite in a much more intimate way than they do in the hydrogen atom, and so form a particle of no nett charge and with a mass nearly the same as that of the hydrogen atom. His view was that with such a particle as the first step in the formation of atomic nuclei from the two elementary units in the structure of matter — the proton and the electron — it would be much easier to picture how heavy complex nuclei can be gradually built up from the simpler ones. He pointed out that this neutral particle would have peculiar and interesting properties.
- "The Neutron and Its Properties, Nobel Lecture, December 12, 1935". Nobel Lectures, Physics 1922-1941. Amsterdam: Elsevier Publishing Company. 1965. p. 339–348. (quote from p. 339)