William Draper Harkins, the first to predict the existence of the neutron and to propose the basic principle of nuclear fusion

December 28, 1873, Titusville (Pennsylvania, United States of America) - March 7, 1951, Chicago (United States of America)

Between 1900 and 1912, he was a professor of chemistry at the University of Montana and received his doctorate in 1908 from Stanford University (USA).

In 1912 he moved to the University of Chicago where he spent the rest of his professional career.

Although he is best known for his contributions to surface and nuclear chemistry and for being one of the first environmental chemists, he also investigated atomic theory, in particular, the structure of the atomic nucleus and aspects of nuclear radioactivity. Among his achievements are:

• Introduce concepts such as ‘packing defraction’, a measure of the energy involved in the association of protons and neutrons within the nucleus of an atom.
• Correctly predicted the existence of the neutron in 1920 (as a proton-electron complex) and was the first to use the word ‘neutron’ about the atomic nucleus (the neutron was detected experimentally by James Chadwick in 1932).
• He predicted the existence of heavy hydrogen (or deuterium)
• He was the first to propose the basic principle of nuclear fusion in 1915, four years before Jean Baptiste Perrin published his theory in 1919-1920. Using Albert Einstein's concept of the equivalence of mass and energy, he showed that by combining four hydrogen atoms to produce one atom of helium, a small amount of mass would be converted into energy; he correctly theorised that this process was a source of stellar energy.
• In the early 1930s, he contributed to the second cyclotron with fellow University of Chicago scientist Robert James Moon, greatly improving its design. Experiments with Moon analysing the fusion processes between hydrogen and helium led him to conclude, correctly, that the fusion of hydrogen atoms and the subsequent production of helium was the energy-generating mechanism in the Sun and stars.
• He developed one of the first cosmological models that attempts to explain the abundance in the universe of each of the chemical elements in the periodic table, i.e. he made one of the first attempts to calculate the proportions of the elements in the universe.

Between 1909-1910, as a visiting professor with Fritz Haber, he was introduced to the study of surface tension and began work on solution and solvation theory during a visit to the Massachusetts Institute of Technology (MIT).

Other scientists at the University of Chicago used this cyclotron, including Enrico Fermi, who performed neutron scattering experiments.

In 1921, Harkins was elected to the US National Academy of Sciences and, in 1925, to the American Philosophical Society.

Since 1978, the magnetic yoke of the cyclotron built by Harkins has been on display at the Fermi National Accelerator Laboratory (FERMILAB).

Among his students were: Robert Mulliken, Lyle Bejamin Borst, Calvin Souther Fuller, Martin Kamen, Henry W. Newson, Samuel Allison and Robert James Moon.