Ernest Thomas Sinton Walton | Biography

Ernest Rutherford's discovery of the atomic nucleus in 1911 neatly solved one problem in atomic theory--the relative distribution of positive and negative charges in the atom. Consequently, new questions regarding the structure and composition of the nucleus itself were raised.

One method for answering that question was pursued by Rutherford himself. He directed alpha particle s from naturally radioactive materials at the nuclei of atoms, attempting to "blow apart" those nuclei. The products obtained from such an experiment, Rutherford felt, would reveal the body's composition.

Although Rutherford achieved some success with this research, he also recognized certain limitations. The number and energies of the particles available from natural sources limited his control over the experiment. He had to use whatever particles his source provided him. At the time, no technique was available for accelerating alpha particles, protons, or other particles by artificial means that would give an investigator precise control of his or her experiment.

An important turning point in this line of research occurred in 1928 when George Gamow used wave mechanics to show that particles with relatively low energies had some probability of overcoming the electrostatic force of repulsion from the nucleus and entering the nucleus itself. One of the first workers to recognize the significance of Gamow's finding was John Douglas Cockroft, then a student of Rutherford's. Cockroft convinced Rutherford that a machine could be built that would accelerate particles to a speed sufficient to enter the nucleus. He joined efforts with another of Rutherford's students, Ernest Walton, to build the machine.

In 1932, Walton and Cockroft used this new accelerator to bombard a lithium target with protons. They found that only alpha particles were produced in the experiment. From this they concluded that "... the lithium isotope of mass 7 occasionally captures a proton and the resulting nucleus of mass 8 breaks into two alpha particles of mass 4." The experiment was significant not only because it represented the first nuclear change produced entirely by human means, but also because Cockroft and Walton were able to determine the very large amounts of energy released during the reaction. The latter result also provided confirmation for Albert Einstein's contention that mass and energy are interconvertible. For this work, Walton shared the 1951 Nobel Prize in physics with Cockroft.

Walton was born on October 6, 1903, in Dungorran, Waterford, now in the Republic of Ireland. He studied at the Methodist College in Belfast and earned his bachelor of arts (1926), master of science (1928), and master of arts (1934) degrees from Trinity College at the University of Dublin. During the period 1927-1934, he was also a graduate student at Cambridge, where he worked in Rutherford's laboratory and received his Ph.D. in 1931. He returned to Trinity College in 1934 where he was first a fellow and then, in 1946, Erasmus Smith Professor of Natural and Experimental Philosophy. In 1952, he was appointed chairman of the School of Cosmic Physics at the Dublin Institute for Advanced Studies.