Ernest Walton won the 1951 Nobel Prize in Physics with his colleague John Cockcroft for producing the first artificial nuclear disintegration in history.
Walton & Cockcroft designed and built the first ‘high energy’ particle accelerator. As a remarkable side-benefit, their experiment provided proof that Einstein’s mass-energy equivalence equation E = mc2 is correct.
Achievements and Key Points
- Ernest Walton & John Cockcroft built an electrical transformer to convert low-voltage AC electricity into high voltage DC electricity.
- They used the high voltage to power the first ‘high energy’ particle accelerator in history.
- The particle accelerator produced protons moving at very high speeds.
- The protons smashed into lithium atoms, like high velocity bullets smashing into small rocks.
- The protons penetrated lithium nuclei, causing them to split into helium nuclei – the first time a nuclear transformation had ever been achieved using artificially produced particles.
- The large amounts of energy released by this nuclear reaction provided proof of Einstein’s famous claim that mass and energy are equivalent, related by the equation E = mc2.
- Walton & Cockcroft were awarded the 1951 Nobel Prize for “their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles.”
Early Life
Ernest Thomas Sinton Walton was born on October 6, 1903 at Dungarvan, Ireland, UK.
His father was John Arthur Walton, a Methodist minister who eventually became president of the Methodist church in Ireland. His mother was Anna Elizabeth Sinton, a Quaker. She died in August 1906, before Ernest reached his third birthday.
Ernest’s father was moved to a number of different posts and Ernest attended schools in Banbridge, Cookstown, and Dublin before, at age 12, he became a boarder at the Methodist College Belfast.
Brilliant Scholar
Ernest Walton’s abilities in Mathematics and Physics were conspicuous. At age 18, he won a Mathematics scholarship to Trinity College, Dublin. While at Trinity College he took most of the available Mathematics prizes and also the Brookegold medal for Experimental Science. In 1926, age 22, he graduated with first class honors in both Mathematics and Experimental Science. He began research with the mathematician and physicist Professor J. L. Synge, graduating in 1927 with a Master’s degree in Physics.
PhD with Ernest Rutherford
Walton’s ability was so highly regarded that the great Ernest Rutherford accepted him as a PhD student at the University of Cambridge’s Cavendish Laboratory.
Walton had big ideas and, with minimal money, tried to build a particle accelerator hoping to push charged particles – first he tried electrons, then heavy positive ions – to high energies and smash them into light nuclei to disintegrate them.
In doing so, he hoped to extend Ernest Rutherford’s earlier work – in 1919, Rutherford achieved the first deliberate transformation of one element into another. He converted nitrogen atoms into oxygen atoms by bombarding nitrogen with alpha particles emitted by radioactive elements.
This nuclear reaction was written:
However, using alpha particles to transmute elements only worked in a few specific instances.
Walton hoped to use other particles artificially accelerated to high enough energies to penetrate and split atomic nuclei. His experiments were unsuccessful, but he was awarded his PhD in 1931, age 27.
John Cockcroft
Another postdoctoral fellow at the Cavendish, working on similar lines to Walton, was John Cockcroft, who hoped to crash protons into light nuclei. Rutherford encouraged the pair to work together and gave them £1,000 to build a particle accelerator.
A Particle Accelerator Made from Scrap Splits the Atom
The two scientists made a perfect team and put together an accelerator that looked home-made (it was, including scavenged bicycle parts, glass tubes, food tins, and modeling clay), but it worked. The electrical transformer they built took low-voltage AC electricity and converted it to high voltage DC electricity – the maximum was about 700,000 volts, which was more than enough to accelerate protons to the necessary velocities.
With this equipment, on the morning of April 14, 1932, Walton performed the first artificial nuclear disintegration in history, crashing protons at 400,000 volts into a thin sheet of lithium metal, splitting lithium atoms into fast moving helium nuclei (alpha particles).
“To my delight, I saw tiny flashes of light looking just like the scintillations produced by α-particles which I had read about in books but which I had never previously seen. After making some simple tests to ensure that I was not imagining things, I phoned Cockcroft.”
Walton & Cockcroft carried out further experiments, smashing carbon, nitrogen, and oxygen atoms using protons, deuterons, and alpha particles, producing radioactive isotopes such as carbon-11 and nitrogen-13.
The two scientists were awarded the 1951 Nobel Prize in Physics for “their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles.”
Dublin and Marriage
In 1934, age 31, Walton became a Fellow of Trinity College Dublin, where his physics lectures were savored by students as models of splendid clarity.
Also in 1934, Walton married Freda Wilson, daughter of a Methodist Minister. They had two sons and three daughters: Alan, Marian, Philip, Jean, and Winifred. Both sons became physicists.
In 1946, Walton became Erasmus Smith’s Professor of Natural and Experimental Philosophy at Trinity College Dublin.
Faith
Walton was a devout Methodist. He said Science was a way of knowing more about God.
Retirement
Walton retired in 1974, age 71. He died, age 91, in Belfast on June 25, 1995. He was buried in Deansgrange Cemetery, Dublin, Ireland.
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Further Reading
Brian Pippard
Walton, Ernest Thomas Sinton (1903–1995)
Oxford Dictionary of National Biography, May 2006
https://doi.org/10.1093/ref:odnb/57946
Ernest Walton
Recollections of Nuclear Physics in the Early Nineteen Thirties
Europhysics News, Vol. 13, No. 8/9, August/September 1982