The other Nobel man


Most people would reckon they had been given an easy question if asked: "Name Ireland's Nobel prize winners"?. They spring readily to mind - William Butler Yeats (1923), George Bernard Shaw (1925), Samuel Beckett (1969), Betty Williams and Mairead Corrigan (1976), Seamus Heaney (1995), John Hume and David Trimble (1998). But this answer would be incomplete.

Ireland has produced another Nobel laureate, the only Irish person to win the prize for science, Ernest Thomas Sinton Walton (1903-1995). Walton was awarded the Nobel prize in physics in 1951 jointly with J. D. Cockroft, for "splitting the atom".

Ernest Walton was born in Dungarvan, Co Waterford, in 1903, son of a Methodist minister, John Walton, and Anne E. Sinton. Ernest received his early education in Banbridge and Cookstown and secondary education at Methodist College, Belfast. He entered Trinity College, Dublin, in 1922 on scholarship and took a first-class honours degree in physics and mathematics (1926), followed by an MSc degree in 1927. He won a research scholarship to work with Ernest Rutherford (1871-1937) at the famous Cavendish Laboratory at Cambridge.

At the time, physics was going through a golden era. Albert Einstein had revolutionised the way physicists looked at the world with his theory of relativity (1905, 1915). Rutherford had discovered that atoms have a tiny dense central core, the atomic nucleus, in 1910. A cloud of electrons surrounds the atomic nucleus and Niels Bohr had described how the electrons orbit the nucleus in 1913. And in 1925 and 1926, Werner Heisenberg, Paul Dirac and Erwin Schr÷dinger founded a new branch of physics, quantum mechanics, whichdescribes the behaviour of atoms and sub-atomic particles.

By 1927, the focus of atomic research had moved to the atomic nucleus. In order to prise the nucleus open to examine its internal structure, it has to be hit with highly energetic particles of its own size or smaller. Walton's first job in Rutherford's laboratory was to build an apparatus capable of accelerating electrons (much smaller particles than the atomic nucleus) to very high speeds. Although this project worked well, the speeds achieved remained too slow to break open an atom.

In 1929, J. D. Cockroft joined Walton and they worked to develop an apparatus to accelerate positively charged particles, protons, (electrons are negatively charged) to high velocities. Walton's great technical skill and experimental ingenuity helped to develop the apparatus despite the scarce resources available - they relied in part on car batteries and bits of petrol pumps. They built an accelerator capable of developing a voltage up to 700,000 volts for the acceleration of protons. (Atomic nuclei are composed of two types of particles, protons and neutrons, both of the same size, but the proton has a positive charge whereas the neutron has no charge.)

On April 14th, 1932, Walton and Cockroft used their proton accelerator to bombard a target made of lithium, the third lightest natural element. The lithium nucleus contains three protons and four neutrons. The proton bombardment induced the lithium nucleus to disintegrate into two alpha particles, each composed of two protons and two neutrons, and those disintegrations produced little flashes of light on a "scintillation screen".

This was the first time an artificial disintegration of an atomic nucleus was witnessed. The results were published in the scientific journal, Nature, on April 30th, 1932.

The atom-splitting experiment grabbed the public imagination and the significance of the work was immediately appreciated by the scientific community. It was now possible to split the atomic nucleus in a controlled process. The Walton-Cockroft experiment also confirmed a number of scientific predictions arising out of relativity theory and quantum mechanics. It demonstrated that a large amount of energy could be released in a nuclear reaction and provided the first experimental verification of Einstein's famous mass-energy equivalence equation: E=MC 2 - where E is energy, M is mass and C is the speed of light. The combined mass of the two alpha particles is slightly less than the lithium nucleus plus proton, the missing mass being converted into energy.

The Walton-Cockroft particle accelerator sparked off a huge amount of scientific research.

Ernest Walton returned to Ireland and became a Fellow of TCD in 1934. He married Winifred Wilson and they had two boys and two girls, all of whom took up science careers. Alan, the eldest, is a physicist at the Cavendish Laboratory. Marian became a physics schoolteacher, Philip is professor of medical physics at NUI Galway, and Jean became a biology schoolteacher.

Walton was appointed Erasmus Smith Professor of Natural and Experimental Philosophy at TCD in 1946 and was head of the physics department until his retirement in 1974. In addition to his work on disintegration of atomic nuclei, he published work on microwaves, hydrodynamics and the focusing of charged particles.

The citation for the award of the Nobel prize to Walton and Cockroft in 1951 recognised "their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles".

Prof Walton was highly regarded as a teacher. His technical brilliance and manual dexterity made him a master of the lecture-demonstration. The many students who attended his lectures, from his return to Ireland in 1934 to his retirement in 1974, fondly remember him.

William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.