Walton

In the early afternoon of Thursday the fourteenth of April 1932, in the small high-voltage laboratory at the back of the Cavendish Laboratory in the basement of the New Museums building on Free School Lane in Cambridge, the Irish-born twenty-eight-year-old physicist Ernest Walton and his English-born senior collaborator John Cockcroft, then thirty-four, fired the world's first artificial particle-accelerator beam at a lithium-metal target and produced the first artificial nuclear disintegration in the history of physics. The accelerator (the Cockcroft-Walton voltage-multiplier circuit and the long evacuated glass column that delivered a beam of about three hundred kiloelectronvolt-energy protons against the lithium target) had been built across the previous three years on the floor of the Cavendish high-voltage room. Walton, at the controls on the afternoon of the fourteenth, watched through the small lead-glass observation window at the back of the column as the lithium target on the receiving end produced the characteristic faint blue scintillations of alpha-particle emission, the signature in the zinc-sulphide screen behind the target of the splitting of the lithium-7 nucleus into two helium-4 nuclei by the incoming proton beam. He left the observation window, walked across the basement laboratory to fetch Cockcroft, and the two men confirmed the observation across the next hour. They had artificially split the atom. The result, published in Nature on the thirtieth of April 1932 under the title Disintegration of Lithium by Swift Protons, was the foundational experimental result of modern nuclear physics, the first demonstration that one element could be artificially transmuted into another, and the central single technical breakthrough on which the Manhattan Project of 1942 to 1945 and the nuclear age of the twentieth century would rest. Cockcroft and Walton shared the Nobel Prize in Physics in 1951 for the discovery.

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