I reasearched about the history of the discovery of neutrons and couldn't find who found out that isotopes are a change in the number of neutrons. Can you please tell me who it was that made this discovery?
From Pauling's "General Chemistry" (ref. 1):
In 1921 the American chemist W.D. Harkins described nuclei as being built of protons and neutrons; he used the word "neutron" for a hypothetical particle with mass equal to that of the proton and with no electric charge. Ernest Rutherford made a similar suggestion during the same year. In 1932 the discovery of tne neutron was reported by the English physicist James Chadwick (born 1891).
The original article in which Harkins (ref. 2) reported this hypothesis is linked by the Wikipedia:
- Linus Pauling, General Chemistry, second edition, 1970, p. 102
- Harkins, William (1921). "The constitution and stability of atomic nuclei. (A contribution to the subject of inorganic evolution.)". Philos. Mag. 42 (249): 305.