Monday is the 71st anniversary of the first experiment to split the atom, a feat accomplished by Ireland's sole Nobel Prize-winning scientist. Bill Davis reports.
This year marks the centenary of the birth of Ireland's only winner of a Nobel Prize for science, the physicist Ernest Walton. He shared the 1951 physics award with John Cockcroft, with whom he was the first person to split the atom. The two accomplished the feat while conducting research at the famous Cavendish Laboratory at Cambridge University, 71 years ago next Monday.
Walton was born in Dungarvan, Co Waterford, on October 6th, 1903. As a youngster, he was sent as a boarder to Methodist College in Belfast. There he was a diligent pupil, especially in mathematics and the sciences. In 1922, following a two-day examination, he was awarded one of the entrance scholarships to Trinity College, Dublin, called sizarships. These were valuable not only because they exempted students from paying fees but also because they provided an evening meal - commons - for the four years of the undergraduate physics and mathematics course.
By the time he started his postgraduate research, in 1926, Trinity's physics department was in the doldrums, an uninspiring place for a bright young man full of original ideas. The exciting place to be was the Cavendish Laboratory, where three Nobel Prize winners were in charge. Fortunately, in 1927 Walton won a doctoral scholarship to Cambridge under the supervision of one of the Nobel laureates, the New Zealand-born Ernest Rutherford.
Rutherford had long worked at trying to understand the structure of the atom, particularly through the study of radioactivity. In 1919, he had identified the high-energy particles emitted from some disintegrating radioactive substances. These he named alpha particles.
He had used these natural high- energy particles to force changes in the nuclei of various atoms. What was needed, however, was a means of artificially producing a stream of these particles under human control. Already a number of able people were working at the Cavendish on the problem, including John Cockcroft, six years older than Walton and with considerable skills in engineering.
Rutherford suggested to Walton one method that might energise negatively charged electrons. After about five months' effort, Walton decided it was not going to work. Instead he suggested to Rutherford that he build an apparatus to speed up lightweight but positively charged particles, such as hydrogen ions. Walton started to build, Cockcroft helping with the engineering problems. It was three years before it was ready for the crucial experiment. Walton and Cockcroft spent much time making their "linear accelerator" as perfect as possible. It was only when Rutherford, impatient with what he regarded as slow progress, told them to "get on with the job" that they decided to use their beam of protons in an attempt to split lithium, a small and simple atom.
They hoped a proton from the linear accelerator penetrating the nucleus would cause the lithium atom to break up, causing pieces of the nucleus to fly apart. Detection of these pieces, appearing as faint flashes on a fluorescent screen, would be evidence of having split the atom.
It was these very flashes Walton observed on the morning of April 14th, 1932. They were caused by alpha particles formed in the atomic disintegration. Walton had used a narrow wooden packing case as a darkroom to help him observe the flashes through a microscope. When Rutherford, a big man, was called to view them, he could hardly get into the packing case - but when he did, he confirmed the first artificial splitting of an atom.
A fortnight later, a short letter published in the journal Nature told the story and caused a stir in scientific circles round the world.
Walton continued his collaboration with Cockcroft for another two years, after which their careers took very different paths. Cockcroft was to become a leading light in Britain's nuclear research institutions. Walton, who died in 1995, decided to return to Trinity as a member of staff in his former department. Here he was to inspire a generation of physics students by his teaching, including members of his own family.
After the dropping of nuclear bombs on Hiroshima and Nagasaki, he became an active member of Pugwash, an international organisation whose aim was to stop the use of nuclear energy as an instrument of war.
In 1951, he and Cockcroft were jointly awarded the Nobel Prize, not only for their experiment of 19 years previously but also for creating the stimulus that had inspired so many subsequent discoveries in nuclear physics. As the Nobel citation stated: "This work may be said to have produced a totally new epoch in nuclear research."
Dr Bill Davis teaches the history of science at the Open University in Ireland. He is a contributing editor of Irish Innovators In Science And Technology (Royal Irish Academy, €27.50)