In a Cambridge laboratory in the spring of 1932, two physicists achieved something that had been the dream of science since the ancient Greeks first imagined the atom: they split it. By accelerating particles and firing them at the nucleus of an atom, they broke it apart, confirming Einstein's famous equation linking mass and energy and opening the door to the nuclear age. One of those two men was an Irishman from County Waterford named Ernest Walton — and to this day he remains the only Irish-born scientist ever to win a Nobel Prize in a science.
Quick answer: Ernest Walton, born in Dungarvan, County Waterford, in 1903, was the first person, together with John Cockcroft, to split the atomic nucleus by artificial means, in 1932 at Cambridge. Using a particle accelerator they built, they bombarded lithium with protons and broke its nucleus apart, confirming Einstein's mass-energy relationship. For this achievement Walton and Cockcroft shared the 1951 Nobel Prize in Physics. Walton remains the only Irish-born winner of a Nobel Prize in the sciences.
Who was Ernest Walton?
Ernest Thomas Sinton Walton was born on October 6, 1903, in Dungarvan, County Waterford, the son of a Methodist minister whose calling moved the family around Ireland during Walton's childhood. He proved an outstanding student, particularly in mathematics and science, and won a scholarship to Trinity College Dublin, where he excelled in physics and mathematics. His brilliance earned him a research scholarship to the Cavendish Laboratory at Cambridge, then the greatest centre of experimental physics in the world, under the leadership of Ernest Rutherford.
It was at the Cavendish, in the late 1920s and early 1930s, that Walton found himself at the very frontier of physics, among a remarkable group of scientists probing the structure of the atom. Working closely with the English physicist John Cockcroft, Walton set about one of the great challenges of the age: building a machine that could accelerate particles to high enough energies to penetrate and break apart the nucleus of an atom. It was painstaking, difficult work, demanding both theoretical insight and great experimental skill.
How did Walton split the atom?
The challenge Walton and Cockcroft faced was immense. The nucleus of an atom is held together by powerful forces and shielded by its positive charge, which repels other positively charged particles. To break into it, they needed to accelerate protons to enormous speeds and energies. Together they designed and built an apparatus, now known as the Cockcroft-Walton generator, that could generate the very high voltages needed to accelerate particles to the required energies — a major feat of experimental engineering in itself.
On April 14, 1932, they directed their beam of accelerated protons at a target of lithium, and observed the result: the lithium nuclei split apart into helium nuclei, releasing energy exactly as predicted. They had become the first people in history to split the atomic nucleus by entirely artificial means, transmuting one element into another by deliberate human action. Crucially, their careful measurements confirmed Einstein's equation relating mass and energy, demonstrating that a tiny loss of mass had been converted into energy. It was a landmark in the history of physics, the experimental dawn of the nuclear age.
Was it really the first time the atom was split?
Some care and honesty are needed with the famous phrase splitting the atom, because the history is often muddled. Earlier physicists, notably Rutherford himself, had already managed to alter atomic nuclei using natural particles emitted by radioactive substances. What made the Walton and Cockcroft achievement distinct and historic was that they were the first to split the nucleus using artificially accelerated particles — particles sped up by a machine they had built, rather than relying on natural radioactivity. This gave physicists, for the first time, deliberate control over the process.
It is also right to acknowledge that this was a shared achievement: Walton and Cockcroft worked as a partnership, and they shared the Nobel Prize equally. The work also built on the theoretical insights of others, including the physicist George Gamow. None of this diminishes Walton's role; he was an equal partner in one of the defining experiments of twentieth-century physics. The honest and proud statement is that an Irishman from Dungarvan was one of the two men who first split the atom by artificial means, and was justly rewarded with the Nobel Prize for it.
What was Walton's legacy?
After his Cambridge triumph, Ernest Walton did something that tells us much about the man: he returned home to Ireland. He took up a professorship at Trinity College Dublin, where he spent the rest of his career teaching and inspiring generations of Irish students, declining the opportunities to pursue fame and fortune abroad that his Nobel Prize might have brought. In 1951 he and Cockcroft were awarded the Nobel Prize in Physics, and Walton became, and remains, the only Irish-born scientist to win a Nobel in a scientific field.
His decision to build his life and career in Ireland makes him a particular source of national pride — a world-class physicist who chose to give his gifts to his own country's students. He died in 1995, remembered with deep affection in Ireland. Walton's achievement, splitting the atom and confirming the equivalence of mass and energy, stands among the very greatest in the story of Irish inventors and scientists who changed the world — the Waterford man who helped open the nuclear age and then came home to teach.
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