In 1898, Rutherford obtained the physics professorship at McGill University, Montreal, and soon demonstrated his talents by discovering several radioactive elements. Although others had pioneered the earliest developments in radioactivity, Rutherford soon achieved dominance in this field. He found that at least two kinds of radiation, which he labeled alpha and beta, existed. Working with Frederick Soddy in 1902-03, Rutherford identified the phenomenon of radioactive half-life and formulated the still-accepted explanation of radioactivity: each decay of the atoms of radioactive materials signifies the transmutation of a parent element into a daughter, with each type of atom having its own transformation period. This theory stimulated many other scientists, including Rutherford, to order all known radioactive elements into their decay series and to search for any missing members. Rutherford was awarded the 1908 Nobel Prize for chemistry for his work in radioactivity. Moving to the University of Manchester in 1907, Rutherford almost immediately began to examine alpha particles because, since they were relatively massive and of atomic dimensions, he felt that they were the key to understanding the nature of matter. Indeed, Rutherford and Hans Geiger showed (1908) conclusively that alpha particles were doubly charged helium ions.
Rutherford made his greatest discovery in 1909. Shortly after his move to Manchester, he found that a few alpha particles, when bombarding thin metal foils, were deflected from their incident beam through more than 90 deg. "It was almost as incredible," Rutherford later responded in a now-classic statement, "as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you." Early in 1911 he finally announced his version of the structure of the atom: a very small, tightly packed, charged nucleus sprinkled with opposite charges in the mostly empty surrounding void. The deflected alpha particles were those that had come into close proximity with the nucleus and had rebounded in various oblique directions.
About the time that Rutherford moved (1919) to Cambridge to succeed Thomson as director of the Cavendish Laboratory, he discovered artificial disintegration--the artificial splitting of the atom--a signal discovery that presaged his entry into the field of nuclear physics. Members of his Cavendish team discovered the neutron and the disintegration phenomena produced by artificially accelerated particles.
Rutherford was president (1925-30) of the Royal Society, which had given him its highest award, the Copley Medal, in 1922. Rutherford was knighted in 1914, raised to the peerage in 1931, and awarded the Order of Merit in 1921.