ved him well in later years. Nowadays, modern accelerator science and engineering relies on such a broad application of skill and innovation.
Such a diverse and formidable combination of training in mathematics, physics and engineering, plus practical experience with a local electrical company, primed Cockcroft for his future success. He joined Ernest Rutherford, who had recently moved from Manchester to the Cavendish Laboratory and with whom he had worked as an apprentice back in Manchester. Initially Cockcroft worked with Peter Kapitsa in the high-magnetic-field laboratory, where he used his industrial links to obtain the necessary large-scale equipment.
At the time, Cockcroft was in many ways the Cavendish Laboratory's only true "theoretician", bringing his mathematical abilities as well as his pragmatic engineering skills to a group that was strong in the experimentalist tradition of Rutherford. Cockcroft realized in 1928, before anyone else, the implications of Gamow's tunnelling theory, namely that an energy of 300 keV might be sufficient for protons to penetrate a nucleus of boron, and even less for lithium. In a seminar at the Cavendish Laboratory in 1928 the young Soviet physicist Georgij Gamov (who became better known as George Gamow) reported on his calculations of potential-barrier tunnelling, its successful application to alpha-decay, and its importance for barrier penetration. Encouraged by Rutherford, Cockcroft initiated the high-voltage accelerator programme, and was joined by a student, Ernest T S Walton from Ireland.
Walton was a Methodist minister's son, born in 1903 and educated in Belfast and Dublin. He was very much the lead experimentalist, though the junior partner. The aim was to build an accelerator to achieve an energy up to 1 MeV in order to be sure to penetrate the nuclear potential barrier. Walton had abandoned work on a circular accelerator for his thesis topic and now pursued the linear solution with Cockcroft. They took advantage of strong links with Cockcroft's old employer in Manchester, Metrovick, which at the time was pioneering equipment for the UK electrical grid at transmission voltages up to 130 kV. Metrovick supplied the high-voltage transformers for what became the Cockcroft–Walton generator. So even at the start of the nuclear age, academic–industrial collaboration underpinned progress.
There were formidable challenges to overcome in each component: motor, generator and transformer; rectifier; 40 kV proton source; glass vacuum vessel; and so on. To this day working with such voltages, even below 500 kV, causes difficulties, as witnessed by the performance issues faced in DC photo-injectors at Jefferson Laboratory and Daresbury Laboratory. The interesting story of scrounging for the proper ceramic tubes to be used in the ultimate Cockcroft–Walton generator is a saga in itself.
Records show that life at the Cavendish Laboratory under Rutherford did not begin early in the day and finished strictly at 6.00 p.m. Rutherford insisted that it was to preserve health and to aid contemplation. Perhaps it partly explains the relatively slow progress by Cockcroft and Walton between 1929 and the ultimate triumph in 1932, although perhaps also it was, by all accounts and like all experimentalists, because both enjoyed the fun of building and perfecting their new experimental "toy". Another reason was the relocation of their laboratory and a rebuild of their apparatus to a nominal 800 keV rating, primarily because of their own lack of confidence in the predictions of the new tunnelling calculations.
The day that transformed subatomic physics was 14 April 1932 when Cockcroft and Walton split the lithium atom with a proton beam. Accounts have it that Rutherford had become frustrated at the lack of results from the generator, which was Cockcroft and Walton's pride and joy, and insisted that they get some results. Initially they used a beam of 280 keV, but later demonstrated atom splitting by a beam with energy below 150 keV. The experimenters closeted themselves in a lead-lined wooden hut in the 