Robert McNees
Physicist Ernest Rutherford was born in Brightwater, New Zealand #OTD in 1871.
He discovered the nucleus, proton, and α and β particles; explained nuclear decay; and was the first person to successfully transmute one element into another.
Image: George Grantham Bain Collection, LOC
Robert McNees
During Rutherford’s first stint at Cambridge he worked with JJ Thomson on projects that contributed to the discovery of the electron.
In 1898, while still at Cambridge, he reported on two types of radiation that he’d later refer to as “α” and “β” rays.
Rutherford then went to McGill, in Montreal, where he continued to work on radioactivity. It was there he developed his “disintegration theory,” pinpointing some form of atomic breakdown as the source of radioactivity.
Robert McNees
This work was awarded the 1908 Nobel in Chemistry.
But Rutherford's (arguably) most significant discovery came after his Nobel prize. He had moved on to Manchester, and was studying the scattering of alpha rays.
In 1909, with Geiger and Marsden, Rutherford scattered α particles off of a thin gold foil. I've seen the foil thickness estimated at 2800 atoms. He noticed that an α occasionally scattered off the foil at large angle, and sometimes even back-scattered directly towards the source!
Robert McNees
“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
[Andrade, E. N. da C., Rutherford and the Nature of the Atom, p. 111 (1964)]
Robert McNees
These observations were at odds with Thomson’s prevailing model of the atom – “plum pudding” electrons situated throughout a large positively charged blob. That model wouldn’t produce the scattering events Rutherford and his collaborators were seeing.
Instead, Rutherford hypothesized that an atom’s positively charged components and most of its mass must be concentrated in a comparatively tiny nucleus. Head-on collisions with an α would be rare (since the nucleus is so small) but dramatic!
Robert McNees
During this period Rutheford brought a young physicist named Niels Bohr to his lab. Conceptual problems with the Rutherford model of the atom (why don’t the electrons crash into the nucleus?) prompted Bohr’s development of his quantum mechanical model.
Rutherford left Manchester for Cambridge in 1919, to lead the Cavendish labs. But before his departure he made one last remarkable discovery: by bombarding nitrogen with alpha particles, he triggered the process ¹⁴N + α → ¹⁷O + p.
Robert McNees
Technically this was the first time someone had intentionally transmuted one element into another.
Rutherford suspected this might be what happened, but he reported his findings very carefully and adopted a conservative point of view pending more evidence.
But it is fair to say that Ernest Rutherford was the first successful alchemist.
Robert McNees
An important consequence of this experiment was Rutherford’s identification of the hydrogen nucleus as a fundamental particle in its own right. He dubbed it the “proton."
A few years later he hypothesized the neutron, which would account for the non-proton mass of nuclei and somehow hold them together. Ten years later his former doctoral student Chadwick would discover the neutron, there at Cavendish labs.
Robert McNees
Rutherford’s investigations into elemental transmutation would inspire Leo Szilárd’s idea of producing energy via nuclear chain reactions.
Besides his discoveries, Rutherford trained several notable scientists. I already mentioned Niels Bohr, Otto Hahn, and Hans Geiger.
A lesser known but very important scientist he trained was Harriet Brooks. She was Rutherford's first grad student, and probably the first human to notice the recoil of an atomic nucleus due to emissions during nuclear decay
Jon Het-CIS.
@mcnees He also built one of the very first radio transmitters. Possibly the first.
Daniel Marks
@mcnees So by turning one element into another, he was the first alchemist. But he was humble and didn't flaunt his wizard hat often.
Robert McNees
@kenkousen Thank you!
Ken Kousen
@mcnees
Just in case you don't get enough encouragement, I thought I'd mention I really enjoy your biographical posts :-)
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