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The Metal of Uranus: The Neglected Element That Changed the World

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We live in a nuclear age, and uranium is the metallic element that fuels the nuclear power plants of the world; indirectly, it also provides the materials for nuclear weapons. In the near future, countries with significant deposits of uranium may become as politically powerful as were the oil-producing countries in the recent past.

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Yet uranium has not always been an important resource. The German chemist Martin Klaproth discovered it by accident in 1789. He had been analyzing a sample of the mineral ore pitchblende from a silver mine in what is today Czechoslovakia. The dark, heavy mineral had been mined in substantial quantities because it was thought to contain some silver. When no silver was found, the pitchblende was thrown away with the debris.

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Sometimes known as black tin ore, pitchblende had variously been identified as a compound of iron, zinc, or tungsten. But after months of diligent experimentation and analysis, Klaproth found that it contained a metallic element completely unlike any other known metal. He named it after a recently discovered planet, Uranus.

Uranium is a relatively common metal – more common than silver, for example – and is found in granite and sand stone rocks in North America, southern Africa, and in small traces in seawater. It is a dense, lustrous material that tarnishes rapidly when exposed to oxygen.

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Yet initially only chemists and mineralogists showed any interest in uranium. Apart from small-scale applications, such as making yellow paint and coloring glass and china, no practical use was made of the new element. Of far more importance was the pitchblende ore which it was first found.

Image Making

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In 1896 the French physicist Henri Becquerel noticed that pitchblende had one very unusual property: photographic plates exposed to a sample of pitchblende reacted as if they had been exposed to light. This property was called radioactivity, but at the time many scientists dismissed it as being of little importance. However, the investigation of what caused the radioactivity was to lead to one of the most significant discoveries in science, a discovery that laid the foundations for modern nuclear physics.

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It was the husband and wife team of Pierre and Marie Curie who in 1898, after years of painstaking experiments, first isolated the element in pitchblende responsible for the radioactive effect. They named it radium, and obtained about one centigram of the pure element for every ton of pitchblende processed.

Radium exposes photographic plates because the nucleus of its atom is unstable and breaks down, releasing particles and electromagnetic radiation. Although uranium is also radioactive, it went almost unnoticed, since it is much less so then radium. In terms of the radioactivity each emits, the two could be compared to a searchlight and a candle.

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All interest, therefore, focused on obtaining radium from the pitchblende ore. Uranium itself was considered an undesirable by-product. For example, every ton of ore processed at the Great Bear Lake refinery in Canada in the 1930’s produced one gram of radium and about half a ton of uranium, for which few uses were found.

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The breakthrough arrived in 1938 when it was proved that uranium atoms, when bombarded with neutron particles – found in the nucleus, or center, of all atoms – split into two. When they split, furthermore, the uranium atoms released neutrons of their own – which could in turn split other uranium atoms. Thus a chain reaction of fissioning uranium atoms could be started. It was this principle upon which development of both the nuclear reactor and the atom bomb would be based.

Fission

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Only one form, or isotope, of uranium (uranium 235) readily undergoes the fission reaction. This isotope accounts for less than 1 percent of naturally occurring uranium. The rest is mainly the comparatively stable uranium 238, which explains why natural deposits of uranium do not spontaneously become reactors or nuclear bombs.

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Scientific progress was rapid after the initial discovery of the fission reaction. From their understanding of nuclear processes, physicists knew that if they could make the fission reaction occur in uranium with a high percentage of 235 isotope, large amounts of energy would be released.

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 The first controlled fission reaction was carried out in December 1942. The first uncontrolled fission reaction – the first atom bomb – was exploded at Alamogordo, New Mexico, in July 1945. Three weeks later the Japanese city of Hiroshima became the first target of nuclear weapons in war. For better or worse, uranium had become an element of destiny in world affairs.

The Nuclear Age

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 The technological advance of the nuclear industry has been accompanied by an increasing unease about the safety of nuclear power. Opponents point to reactor failures, such as the threat at Three Mile Island in the United State and at Chernobyl in Ukraine, which released harmful radioactivity into the environment. Nuclear power stations also produces radio active wastes – wastes that will have to be safely stored for hundreds of years.

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Today in some parts of the world the future of nuclear energy, and of uranium, hangs in the balance. Many countries are trying to develop safer, cleaner technologies, such as solar power. If such projects eventually replace nuclear energy, and the word lays its nuclear armory aside, uranium may once again become the neglected element it was a hundreds years ago.