tended to use a "string and sealing wax" approach to experimental equipment. Oliphant had to buy his own equipment, at one point spending £24 () of his allowance on a vacuum pump. Oliphant submitted his PhD thesis on The Neutralization of Positive Ions at Metal Surfaces, and the Emission of Secondary Electrons in December 1929. For his viva, he was examined by Rutherford and Ellis. Receiving his degree was the attainment of a major life goal, but it also meant the end of his 1851 Exhibition Scholarship. Oliphant secured an 1851 Senior Studentship, of which there were five awarded each year. It came with a living allowance of £450 per annum () for two years, with the possibility of a one-year extension in exceptional circumstances, which Oliphant was also awarded. A son, Geoffrey Bruce Oliphant, was born 6 October 1930, but he died of meningitis on 5 September 1933, and was interred in an unmarked grave in the Ascension Parish Burial Ground in Cambridge alongside Timothy Cockcroft, the infant son of Sir John and Lady Elizabeth Cockcroft, who had died the year before. Unable to have more children, the Oliphants adopted a four-month-old boy, Michael John, in 1936, and a daughter, Vivian, in 1938. In 1932 and 1933, the scientists at the Cavendish Laboratory made a series of ground-breaking discoveries. Cockcroft and Walton bombarded lithium with high energy protons and succeeded in transmuting it into energetic nuclei of helium. This was one of the earliest experiments to change the atomic nucleus of one element to another by artificial means. Chadwick then devised an experiment that discovered a new, uncharged particle with roughly the same mass as the proton: the neutron. In 1933, Blackett discovered tracks in his cloud chamber that confirmed the existence of the positron and revealed the opposing spiral traces of positron–electron pair production. Oliphant followed up the work by constructing a particle accelerator that could fire protons with up to 600,000 electronvolts of energy. He soon confirmed the results of Cockcroft and Walton on the artificial disintegration of the nucleus and positive ions. He produced a series of six papers over the following two years. In 1933, the Cavendish Laboratory received a gift from the American physical chemist Gilbert N. Lewis of a few drops of heavy water. The accelerator was used to fire heavy hydrogen nuclei (deuterons, which Rutherford called diplons) at various targets. Working with