🇳🇿Ernest
Rutherford

Ernest Rutherford grew up on a flax farm in rural New Zealand, the fourth of twelve children, and he would eventually split the atom. The distance between those two facts — between the wooden farmhouse in Brightwater and the Cavendish Laboratory in Cambridge where Rutherford served as director and where, under his watch, James Chadwick discovered the neutron and John Cockcroft and Ernest Walton first artificially accelerated particles to split a nucleus — is one of the great journeys in the history of science. He arrived at Cambridge in 1895 on a scholarship, carrying research on the magnetisation of iron by high-frequency discharges, and he left it six decades later (in a coffin, buried in Westminster Abbey, near Newton) having remade the human understanding of matter from the inside out. He remains, by almost any measure, the greatest experimental physicist of the twentieth century.

Ernest Rutherford was born on August 30, 1871, in Brightwater, near Nelson, New Zealand. His mother Martha was a schoolteacher who believed fiercely in education; his father James was a farmer and wheelwright. Rutherford won a scholarship to Nelson Collegiate School, then another to Canterbury College in Christchurch, where he studied mathematics and physical science and showed the combination of practical ingenuity and physical intuition that would define his career. He won a scholarship to the University of New Zealand in 1894 and the following year received an Exhibition of 1851 Science Scholarship — a prestigious award funded from the profits of the Great Exhibition — that brought him to the Cavendish Laboratory at Cambridge, where he worked under J.J. Thomson, who had just discovered the electron and who quickly recognised that Rutherford was something unusual.

His first major research at Cambridge concerned the ionisation of gases by X-rays, newly discovered by Roentgen. He then turned to uranium radiation — discovered by Henri Becquerel in 1896 — and made his first landmark discovery: he demonstrated that uranium emitted not one but two distinct types of radiation, which he named alpha rays and beta rays, distinguished by their penetrating power. (A third type, gamma rays, was identified shortly after by Paul Villard.) In 1898 he moved to McGill University in Montreal, where he had been appointed professor of physics, and it was here that he performed the work that won him the Nobel Prize. Working first alone and then with the chemist Frederick Soddy, Rutherford showed that radioactivity was not a surface phenomenon but involved the actual transmutation of one chemical element into another — that atoms were not the permanent, indestructible entities that chemistry had assumed since Dalton, but were themselves subject to spontaneous decay, shedding particles and energy and becoming entirely different elements in the process. This was a revolution. The Nobel Committee awarded him the prize in Chemistry in 1908 — an assignment that amused him, since he regarded himself as a physicist. "All science is either physics or stamp collecting," he reportedly said, though the Nobel was for the chemistry of radioactive transmutation.

His greatest experiment came in 1909, after he had moved to the University of Manchester. Working with Hans Geiger and the undergraduate Ernest Marsden, Rutherford directed a beam of alpha particles — positively charged helium nuclei — at a thin sheet of gold foil. According to the prevailing model of the atom (Thomson's "plum pudding" model, in which electrons were embedded in a diffuse positive charge like raisins in a cake), alpha particles should pass straight through, perhaps deflected slightly. Instead, a small fraction of the particles bounced back almost directly toward the source. Rutherford later described his astonishment: it was as if you fired artillery shells at tissue paper and they came back and hit you. The only explanation was that almost all of the mass and all of the positive charge of an atom was concentrated in a tiny, dense central region — which Rutherford named the nucleus — surrounded by mostly empty space in which the electrons orbited at relatively enormous distances. The nuclear model of the atom, announced in 1911, is still the model taught in every school in the world. It was correct.

In 1919, Rutherford returned to Cambridge to succeed Thomson as Cavendish Professor of Physics and director of the Cavendish Laboratory — the most prestigious position in British physics. That same year he performed the first artificial nuclear disintegration, bombarding nitrogen gas with alpha particles and producing oxygen and hydrogen. He had split the atom. He also predicted, in 1920, the existence of a neutral particle with approximately the mass of a proton — the neutron — which was not discovered until 1932, when Chadwick found it in Rutherford's own laboratory. Under his directorship, the Cavendish produced a torrent of fundamental discoveries, and eleven of his students or close collaborators went on to win Nobel Prizes of their own. He trained, directly or indirectly, much of the scientific leadership of the atomic age: Niels Bohr, James Chadwick, John Cockcroft, Peter Kapitza, Cecil Powell. He died in 1937, of complications from a strangulated hernia, aged sixty-six — an unexpectedly sudden end for a man who had seemed as solid and permanent as the nucleus he had discovered. He was buried in Westminster Abbey, near Newton and Darwin, beneath a simple inscription.