The men who first split the atom

Did you know that the word “atom” originates from the Greek word “atomos”? The Greek word means uncuttable or indivisible and the choice of the word comes more from philosophical concepts than from scientific studies.

Atoms, as you might well have studied in school, comprise subatomic particles. The first nuclear transmutation of one element (lithium) to another (helium) under complete human control was achieved by physicists John Cockcroft and Ernest Walton on April 14, 1932.

John Cockcroft

Born on May 27, 1897, Cockcroft came from a family of cotton manufacturers in Todmorden in northern England. He went through a varied educational experience, which put him in good stead for what lay ahead in his life.

Before World War I, he studied mathematics at Manchester University in 1914-15. After serving with the Royal Field Artillery during the war, he returned to Manchester – not to continue studying mathematics, but to pursue electrical engineering at the College of Technology. He joined the Metropolitan Vickers (“Metrovick”) Electrical Company for two years as an apprentice, before heading over to St John’s College, Cambridge, to take his Mathematical Tripos in 1924.

In addition to the wide-ranging skill training – seen now as a prerequisite for modern accelerator science and engineering – Cockcroft’s theoretical know-how in mathematics, physics, and engineering, along with practical experience with a local electrical company put him on the right track. When he rejoined renowned New Zealand physicist Ernest Rutherford – with whom he had previously apprenticed in Manchester – at the Cavendish Laboratory, all the ingredients for Cockcroft’s most important contribution were in place.

Following his success in April 1932, Cockcroft went on to head the Magnet Laboratory in Cambridge in 1934. He worked on radar systems for defence in 1939 and became the director of the Chalk River Laboratory in Canada in 1944. When he was back in the U.K. two years later, he was made the inaugural director of the Atomic Energy Research Establishment (AERE), Harwell, playing a pivotal role in ensuring operational success of the world’s first commercial nuclear power station at Windscale.

In addition to holding many powerful and influential positions, both scientific and administrative, Cockcroft’s work was also acknowledged in many ways, including honorary memberships and doctorates from various academies. He died on September 18, 1967, aged 70.

Ernest Walton

Born on October 6, 1903, Walton went to college in Belfast (now in northern Ireland) and studied physics at Trinity College, Dublin (now in the Republic of Ireland). He did his graduate work at Trinity College, Cambridge, working with Rutherford at Cavendish Laboratory. After receiving his PhD in 1931, Walton stayed on as a fellow at Cambridge, working on his now famous experiment with Cockcroft. While Walton was the junior partner in this experiment, he was definitely the lead experimentalist.

Following his greatest success, Walton chose to move away from the frantic pace of work at the Cavendish Lab. He returned to Trinity College, Dublin, in 1934 – this time as a professor. While this meant that he was no longer involved in cutting edge work in particle physics, he, however, was fulfilling a long-held dream.

Walton not only loved teaching, but was also rather good at it, and he stayed in Dublin for the remainder of his career. In fact, when it was announced in 1951 – nearly two decades after their successful experiment – that he, along with Cockcroft, had won the Nobel Prize in Physics for developing the Cockcroft-Walton generator that helped split the atom, it actually came as a surprise to him. He died on June 25, 1995, aged 91.

The Cockcroft-Walton generator

Rutherford gave Cockcroft and Walton, who had come together under him at the Cavendish Lab, the challenging task of figuring out a way to control fast-moving alpha particles or protons such that they could be aimed at targets – enabling them to further probe the nature of the atomic nucleus.

Cockcroft learnt about quantum tunnelling from Soviet physicist George Gamow during his visit to the lab in 1928. According to this phenomenon, a tiny particle could potentially pierce through the nucleus’ energy barrier. This meant that a much lower energy could well achieve their objective, than what they were initially thinking.

While there were several obstacles to be overcome, including working with voltages unheard of in that era, work moved at a rather sedate pace from 1929 up until the ultimate success in 1932. A number of factors could have contributed to the slow progress. Firstly, records clearly show that days at the Cavendish Lab never began early and always ended at 6 p.m. as Rutherford was a strong believer of preserving the health of people and enabling their contemplation. Add to this the fact that both Cockcroft and Walton enjoyed designing, building, and perfecting their experimental “toy” like most other researchers. The relocation of their lab and the rebuilding of their apparatus to 800 keV rating also contributed to the delay.

The day when they finally split the atom was April 14, 1932. With Rutherford losing patience and pushing Cockcroft and Walton to get results, the duo initially used a beam of 280 keV to split the lithium atom with a proton beam. Atoms were split by an artificially produced beam of protons under human control, for the first time ever. Later demonstrations of the atom were achieved with a beam with energy below 150 keV.

The presence of alpha particles produced by breaking the lithium nucleus was confirmed when a zinc sulphide screen nearby lit up with scintillations and glowed. First Walton and Cockcroft, and then Rutherford himself, witnessed what was happening before agreeing that they had indeed split the atom. Cockcroft and Walton shot off a letter titled “Disintegration of lithium by swift protons” to Nature on April 16, and it was published by the end of the month.

In the years that followed, many Cockcroft-Walton generators were produced for a number of major physics labs throughout the world. The ladder-cascade principle to build up the voltage level by switching charge through a series of capacitances, also called Cockcroft-Walton multiplier, remains in use even today.

Cockcroft’s Indian connection

“Human progress has always depended on the achievements of a few individuals of outstanding ability and creativeness. Homi Bhabha was one of these.”

These were Cockcroft’s words when paying tribute to Indian physicist Homi Bhabha, following his death due to a flight crash in 1966.

Cockcroft and Bhabha were both at Cambridge, where they became colleagues and then friends. When Apsara, Asia’s first research nuclear reactor, was commissioned in August 1956, the complete load of enriched uranium was provided by the U.K. One of the factors that made this possible was Cockcroft’s cordial relationship with Bhabha.

Cockcroft’s expertise also played a sizable role in India’s nuclear programme. In fact, he was involved almost right from the start. The newly formed Indian government’s foreign diplomat Vijayalakshmi Pandit had visited him in the U.K. to seek advice on creating an atomic energy enterprise in the country. Cockcroft probably thought that it was going to be in good hands when he learnt that the enterprise was going to be run under Bhabha’s leadership.