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Rutherford, Ernest, 1st Baron Rutherford (of Nelson)

rays physics nuclear nuclei

(1871–1937) New Zealand–British physicist: founded nuclear physics.

Born near Nelson in New Zealand into a wheel-wright’s large family, Rutherford showed wide-ranging ability at school, won a scholarship to Canterbury College, Christchurch, and in his final years there concentrated on mathematics and physics. In his last year there he invented a sensitive radio-wave detector, just 6 years after had discovered radio waves and in the same year that began to use radio for practical purposes. Ernest Rutherford as the youthful professor of physics at McGill University, Montreal.

In 1895 he won a scholarship to Cambridge to work under ; he borrowed money for his passage to England and soon began research on the conductivity produced in air by X-rays, recently discovered by . He was J J Thomson’s first research student. Rutherford became a professor at McGill University, Montreal 3 years later. Within a short period he greatly extended the foundations of nuclear physics, taking advantage of collaboration with the chemist and a good supply of the costly radium bromide. They produced nine papers in 18 months.

Radioactivity had been discovered in uranium in 1896 by , and in thorium by G C Schmidt (1865–1949); had discovered two more radioactive elements, radium and polonium. Rutherford’s studies revealed (1898) that the radioactive emission consisted of at least two kinds of rays; those which were less penetrating he called alpha rays (helium nuclei), and the others beta rays (electrons); 2 years later he discovered a third, and even more penetrating kind, gamma rays (electromagnetic waves). Together with Soddy he proposed in 1903 that radioactive decay occurs by successive transformations, with different and random amounts of time spent between ejection of each of the successive rays, sometimes years and sometimes fractions of a second. While the process is random, it is governed by an average time in which half the atoms of a sample would be expected to decay. This idea that atoms of some elements are not permanent, but can disintegrate, was then revolutionary.

A skilful set of experiments was then designed with T Royds (1884–1955) to examine alpha rays; having found that the mass and charge were correct for helium nuclei, this was finally proved by sending the rays into an evacuated thin glass vessel and observing the build-up of helium gas inside.

In 1907 Rutherford returned to Britain, and in Manchester he extended his study of alpha particles, working with on the detector named after him, and inventing the scintillation screen for observing them. Geiger and E Marsden (1889–1970) made the surprising discovery that about one in 8000 particles striking a gold foil was deflected back from it. As Rutherford put it ‘ . . . quite the most incredible event that has ever happened to me in my life . . . It was almost as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.’ Knowing that collision with a comparatively light electron could not produce such a large deflection, he deduced (1911) that atoms possess a very small but massive nucleus at their centre, holding all the positive charge to balance that of all the electrons about them. This was the first correct model of the atom, and developed it during a 3-month visit by showing which electronic orbits would be allowed by the ‘old’ quantum theory (which had introduced in 1900). When radiation from a radioactive source such as radium passes through a magnetic field, it is split into three types. The gamma radiation (short X-rays) is undeflected and the alpha rays (helium nuclei) and beta rays (electrons) are deflected in opposing directions.

The First World War caused Rutherford to work on sonic methods for detecting submarines, but in 1919 he returned to his research on succeeding J J Thomson as Cavendish Professor of Physics at Cambridge. Another major discovery occurred within months: he observed that nuclei could be made to disintegrate by artificial means, rather than waiting for their natural disintegration. This work he did himself, as young men were not yet back from the war. Alpha particles striking atomic nuclei, such as nitrogen, would knock out a proton to leave a different and lighter nucleus. Between 1920 and 1924 Rutherford and showed that most light atoms could be broken up by using alpha particles. Chadwick’s later discovery of the neutron, and the nuclear disintegrations of heavier atoms achieved by and E T S Walton (1903–95) using a linear accelerator, owed much to discussions with Rutherford. These and other major discoveries in his laboratory made 1932 a ‘marvellous year’ for nuclear physics. He also was involved, together with M Oliphant (1901–2000) and , in the first nuclear fusion reaction (1934) by bombarding deuterium with deuterium nuclei to produce tritium. He had predicted the existence of the neutron, and the deuteron, as early as 1920.

Rutherford initiated and directed the beginnings of nuclear physics. He received the Nobel Prize for chemistry in 1908 and the simplicity and power of his work gives him a place as one of the greatest experimental physicists of all time. In personality he was forceful, exuberant and enormously likable, with physicist friends worldwide, many of them former students of his. He was not, of course, always right; his response to a suggestion that nuclear energy might one day be useful was that the idea was ‘all moonshine’. But that was in the early 1930s; by 1936 he saw some prospect of useful atomic energy.

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