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Prospecting for uranium Rutherford and Geiger (1st of 2) Rutherford and Geiger (1st of 2) Dredge at work, Gillespies Beach Dredge at work, Gillespies Beach Second <em>New Golden Hind</em> expedition Second New Golden Hind expedition Voyages of the <em>New Golden Hind</em> Voyages of the New Golden Hind Atomic Energy Act ... See more Act 1945 Atomic Energy Act 1945 Radioactive minerals A small number of naturally occurring minerals give off invisible radiation as they gradually decay into a more stable form. The term radioactivity was coined by the French physicists Marie and Pierre Curie, who investigated this property in the late 19th century. Radioactivity in rocks and minerals is due to the presence of tiny amounts of radioactive elements, particularly uranium and thorium. Uses Radioactive elements have a range of applications in medicine and agriculture. In the first part of the 20th century scientists theorised that they could be used to generate heat for power stations, and to build a powerful type of bomb. Trace amounts of uranium compounds are found in almost all rock, soil and water, and one uranium isotope (U-235) is highly radioactive. For use in nuclear reactors and weapons, natural uranium must first be enriched with U-235. This form of uranium is capable of sustaining a chain reaction, releasing large amounts of heat. During the Second World War, uranium was used to make the bomb that was dropped on the Japanese city of Hiroshima on 6 August 1945, and to make plutonium for the bomb dropped on the city of Nagasaki three days later. Development of nuclear power followed and uranium became a sought-after global commodity that would take the world – including New Zealand – into the atomic age. The wartime search New Zealand’s first uranium survey was inspired by the British and American demand for uranium for their nuclear weapons programmes in the Second World War. Ernest Marsden, head of the Department of Scientific and Industrial Research (DSIR), initiated New Zealand’s first uranium survey during the war. In 1943, British and American scientists began work on the Manhattan Project to isolate U-235 and make an atomic bomb. While the UK had initiated a Commonwealth search for uranium in 1942, they did not consider New Zealand promising enough to include in the survey. Marsden, however, planned his own search for radioactive minerals in the South Island. In the winter of 1944 a team of DSIR physicists assembled at the Dominion Physical Laboratory in Wellington to prepare equipment for the survey. The following summer, two teams of geologists and physicists began secretly exploring the South Island. Each was armed with a large, unwieldy Geiger counter – used to detect radioactivity. An earlier study of New Zealand soils and rocks had suggested that granitic rocks and the beach sands derived from them would be the most likely source of uranium and other radioactive minerals. Although radioactivity levels were low, the DSIR teams found the most significant levels in the black sand concentrates of the West Coast gold dredges, and spent two months working on the Gillespies Beach dredge sands near Franz Josef.

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