Sir Mark Oliphant, who died on July 14th aged 98, was one of the cluster of outstandingly creative physicists who, by shaping nuclear physics in its infancy, were assigned by fate to crucial roles in the second World War. His particular achievement at the Cavendish laboratory in Cambridge in the 1930s was the first description of hydrogen fusion.
After a distinguished academic career following his return to his native Australia in 1950, he became Governor of South Australia at the age of 70 - an indication of his vigour, as he was the only scientist of international stature to take on a political challenge at this level.
Vigour was of his essence. It was Mark Oliphant who, in 1940, convinced the Whitehall defence scientific committee that atomic weapons were practical, a truth that had been spelt out in a short and highly perceptive paper by the refugee physicists Otto Frisch and Rudolf Peierls.
And it was he who headed the Birmingham University team secretly seeking high-power oscillators for radar. Under his direction, Randall and Boot produced the cavity magnetron - the device which played a crucial role in winning the war in the air by making short-wave radar possible.
In 1941 it was Mark Oliphant again who, with his rival and friend Ernest Lawrence of the US Berkeley Laboratory, finally galvanised the US scientific community out of its indifference to the military significance of nuclear fission.
From then on the possibility that physicists in Nazi Germany were already working toward nuclear weapons concentrated minds in the US as decisively as they had already been in Britain. Teams came together rapidly. Within a year, he had joined the Manhattan Project and worked at Los Alamos on the electromagnetic separation of uranium-235.
After the atom bombs had been dropped on Japan in 1945, Mark Oliphant declared that physics, a subject of great importance and beauty, had been destroyed for ever. He was involved in the formative years of Pugwash, the powerful Einstein-Russell peace-seeking organisation, an involvement to which he returned in the last years of his life. Born in 1901 in Adelaide, where he studied at the university, Mark Oliphant arrived in Cambridge as an exhibitioner in 1927. His greatest personal triumphs in science came in the 1930s, when his friendship with the New Zealander Ernest Rutherford was at its height and when, with the departure of James Chadwick, he became assistant director of the Cavendish laboratory - then the world's leading centre for experimental nuclear physics.
At this time Rutherford was arguing that the notion of useful energy from nuclear interactions was "moonshine", because the very high energy needed to initiate a reaction meant that you would always get back less than you put in. To avoid his displeasure, he waited until Rutherford was away before attempting his next experiment.
Then, with hurriedly lashed-up equipment, he bombarded heavy water vapour with deuterons (heavy hydrogen nuclei) - the first experimental attempt to produce fusion energy. It was unsuccessful - and earned him a stinging reprimand from Rutherford. In 1937, he infuriated Rutherford still further by accepting the chair at Birmingham.
In 1946 Mark Oliphant became the first scientific adviser to the UN atomic energy commission. Later, with Howard Florey and Keith Hancock, he served on the council setting up the Australian National University (ANU).
In 1950 he was invited to take over the research school at the new university - and accepted. He knew that he might be sacrificing his research, and was dismayed to find that the house he had been promised did not exist. It was almost a year before he and his family had a home. Then, armed with some grants and larger premises, he set about building "the most powerful accelerator in the southern hemisphere", but the project failed, becoming known, cruelly, as "the White Oliphant".
At this time, undismayed, he fought for and became a founding member of the Australian Academy of Sciences. After his retirement from the research school in 1970, he became governor of South Australia from 1971-76. In retirement, Mark Oliphant maintained an office at the ANU and, although shaky on his legs, continued to lecture, study, stimulate and disturb those he met. His wife Rosa died in 1987, and he is survived by his daughter, Vivian.
Sir Mark Oliphant: born 1901; died, July 2000