Ernest Thomas Sinton Walton

1903-1995

Irish Physicist

Ernest Thomas Sinton Walton shared the 1951 Nobel Prize for Physics with John Douglas Cockcroft (1897-1967) for their pioneering studies of the transmutation of atomic nuclei by artificially accelerated atomic particles. Cockcroft and Walton had developed the first nuclear particle accelerator, which became known as the Cockcroft-Walton generator.

Ernest Walton, son of a Methodist minister, was born at Dungarvan, County Waterford, Ireland. After attending day schools in Banbridge and Cookstown, Walton was sent as a boarder to the Methodist College, Belfast, in 1915. Having excelled in mathematics and science, he was able to enter Trinity College, Dublin, on a scholarship in 1922. He specialized in physics, and graduated with first-class honors in both mathematics and experimental science. In 1927, he received his M.Sc. degree and a Research Scholarship, and went to Cambridge University to work in the Cavendish Laboratory under Ernest Rutherford (1871-1937). Walton earned his Ph.D. in 1931. From 1932 to 1934, he was a Clerk Maxwell Scholar. He returned to Trinity College in 1934 as a Fellow. He was Erasmus Smith Professor of Natural and Experimental Philosophy from 1946 to 1974. In 1952 he became chairman of the School of Cosmic Physics at the Dublin Institute for Advanced Studies. He was elected Senior Fellow of Trinity College in 1960.

Walton's early research involved hydrodynamics and the production of fast particles by means of a linear accelerator. His first attempts at high-energy particle acceleration failed, but his methods were later developed and used in the betatron and the linear accelerator. A particle accelerator is a device that produces a beam of fast moving, electrically charged atomic or subatomic particles. Walton and Cockcroft joined forces to produce an instrument that could accelerate protons. The high voltage source for their initial experiments was a four-stage voltage multiplier assembled from four large rectifiers and high-voltage capacitors. The acceleration achieved by their apparatus was large enough to cause a reaction with lithium nuclei. Cockcroft and Walton's experimental system for building up high direct voltages could be expanded to levels many times greater than that of the original apparatus.

In 1932, using their new particle accelerator, they disintegrated lithium nuclei by bombarding them with accelerated protons. Cockcroft and Walton observed that helium nuclei were emitted from the lithium nuclei and concluded that when a proton penetrated a lithium nucleus, the lithium nucleus split into two helium nuclei, which were emitted in nearly opposite directions. Their interpretation was later fully confirmed. This was the first time that a nuclear transmutation had been produced by techniques totally under human control. Using their basic technique and apparatus, Cockcroft and Walton investigated the transmutations of many other atomic nuclei and established the importance of accelerators as a tool for nuclear research. When heavy hydrogen was discovered, they carried out experiments using heavy hydrogen nuclei as projectiles. Their experiments produced some atomic nuclei that were previously unknown and provided a valuable method for comparing masses of atomic nuclei.

Within the limits of experimental error, Cockcroft and Walton's analysis of the energy relations in the lithium transmutation they had achieved provided verification of Einstein's law concerning the equivalence of mass and energy. Eventually, more exact investigations based on the same principles gave a complete verification of Albert Einstein's law. In addition to the Nobel Prize in Physics, Walton received many other honors, including the Hughes Medal, and honorary degrees. Walton married Freda Wilson, daughter of a Methodist minister and a student at Methodist College, in 1934. They had two sons and two daughters. Walton died in Belfast in 1995.

LOIS N. MAGNER