Editing Ernest Rutherford (section)

=== Development of proton and neutron theory ===
In 1919–1920, Rutherford continued his research on the "hydrogen atom" to confirm that alpha particles break down nitrogen nuclei and to affirm the nature of the products. This result showed Rutherford that hydrogen nuclei were a part of nitrogen nuclei (and by inference, probably other nuclei as well). Such a construction had been suspected for many years, on the basis of atomic weights that were integral multiples of that of hydrogen; see [[Prout's hypothesis]]. Hydrogen was known to be the lightest element, and its nuclei presumably the lightest nuclei. Now, because of all these considerations, Rutherford decided that a hydrogen nucleus was possibly a fundamental building block of all nuclei, and also possibly a new fundamental particle as well, since nothing was known to be lighter than that nucleus. Thus, confirming and extending the work of [[Wilhelm Wien]], who in 1898 discovered the proton in streams of [[ionized gas]],<ref>{{Cite journal|doi = 10.1002/andp.18943180404|title = Über positive Elektronen und die Existenz hoher Atomgewichte|journal = Annalen der Physik|volume = 318|issue = 4|pages = 669–677|year = 1904|last1 = Wien|first1 = W.|bibcode = 1904AnP...318..669W|url = https://zenodo.org/record/2190505|access-date = 5 September 2020|archive-date = 13 July 2020|archive-url = https://web.archive.org/web/20200713133516/https://zenodo.org/record/2190505|url-status = live}}</ref> in 1920 Rutherford postulated the hydrogen nucleus to be a new particle, which he dubbed the ''[[proton]]''.<ref>{{cite journal |author=Orme Masson |date=1921 |title=The Constitution of Atoms |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |volume=41 |issue=242 |pages=281–285 |doi=10.1080/14786442108636219 |url=https://archive.org/details/londonedinburg6411921lond/page/280/mode/2up }}<br/>Footnote by Ernest Rutherford: 'At the time of writing this paper in Australia, Professor Orme Masson was not aware that the name "proton" had already been suggested as a suitable name for the unit of mass nearly 1, in terms of oxygen 16, that appears to enter into the nuclear structure of atoms. The question of a suitable name for this unit was discussed at an informal meeting of a number of members of Section A of the British Association at Cardiff this year. The name "baron" suggested by Professor Masson was mentioned, but was considered unsuitable on account of the existing variety of meanings. Finally the name "proton" met with general approval, particularly as it suggests the original term "protyle " given by Prout in his well-known hypothesis that all atoms are built up of hydrogen. The need of a special name for the nuclear unit of mass 1 was drawn attention to by Sir Oliver Lodge at the Sectional meeting, and the writer then suggested the name "proton."'</ref>

In 1921, while working with Niels Bohr, Rutherford theorized about the existence of [[neutron]]s, (which he had christened in his 1920 [[Bakerian Lecture]]), which could somehow compensate for the repelling effect of the positive charges of [[proton]]s by causing an attractive [[nuclear force]] and thus keep the nuclei from flying apart, due to the repulsion between protons. The only alternative to neutrons was the existence of "nuclear electrons", which would counteract some of the proton charges in the nucleus, since by then it was known that nuclei had about twice the mass that could be accounted for if they were simply assembled from hydrogen nuclei (protons). But how these nuclear electrons could be trapped in the nucleus, was a mystery.

In 1932, Rutherford's theory of [[neutron]]s was proved by his associate [[James Chadwick]], who recognised neutrons immediately when they were produced by other scientists and later himself, in bombarding beryllium with alpha particles. In 1935, Chadwick was awarded the Nobel Prize in Physics for this discovery.<ref>{{cite web |title=James Chadwick – Facts |url=https://www.nobelprize.org/prizes/physics/1935/chadwick/facts/ |website=The Nobel Prize |publisher=Nobel Prize Outreach AB |access-date=16 June 2023 |archive-date=4 October 2019 |archive-url=https://web.archive.org/web/20191004015954/https://www.nobelprize.org/prizes/physics/1935/chadwick/facts/ |url-status=live }}</ref>