Marcus Oliphant (1901-2000) was an Australian physicist.
Oliphant is largely responsible for pushing the American atomic bomb program into action. While researching radar at the University of Birmingham in 1940, Oliphant received the findings of Otto Frisch and Rudolf Peierls, who had calculated that a uranium-235 atomic bomb was feasible. Realizing that the weapon could turn the tide of war, Oliphant took their findings to British government officials. A special committee of the top nuclear physicists in Britain was formed, code-named MAUD, and tasked with investigating how much U-235 would be needed to produce an atomic bomb. In 1941, the MAUD Committee published a report that estimated that a critical mass of ten kilograms would be large enough to produce an enormous explosion.
Oliphant sent the report to the US Uranium Committee around March 1941 but the Americans took no action. In August 1941, Oliphant flew to the United States to find out why the United States was ignoring the MAUD Committee's findings. When he called on Lyman Briggs, head of the American Uranium Committee, Oliphant was disappointed to find that "this inarticulate and unimpressive man had put the reports in his safe and had not shown them to members of his committee."
After meeting with other members of the Uranium Committee, including Samuel K. Allison, Oliphant visited Ernest Lawrence, James Conant, and Enrico Fermi to explain the urgency of the situation. Oliphant's message eventually made its way to Vannevar Bush, who had recently been named chairman of the National Defense Research Committee. As a result, the Uranium Committee became the S-1 Project of the OSRD and in December 1941, following the attack on Pearl Harbor, the project was dubbed the Manhattan Project.
While studying under Sir Ernest Rutherford at Cambridge University, Oliphant used a particle accelerator to fire heavy hydrogen nuclei (deuterons) at various targets to study its effect on other nuclei. Together with Rutherford, he discovered the nuclei of helium 3 (helions) and tritium (tritons). He also discovered that when they reacted with each other, the particles that were released had far more energy they started with. Energy had been liberated from inside the nucleus, and he realized that this was a result of nuclear fusion.
In the months leading up to World War II, Oliphant became involved with the development of radar, leading a group at the University of Birmingham that included John Randall and Harry Boot. The three pioneered a radical new radar design, the cavity magnetron, making microwave radar possible. In 1939, he obtained a grant from the British Admiralty to develop radar with a wavelength less than 10 centimeters, compared to the best available at the time of 150 cm. The development of radar would prove a major part in defeating the German U-boats, intercepting enemy bombers and in directing Allied bombers throughout the war.