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Uranium
Uranium is a silvery-grey metal that carries the weight of the Earth's history in its atomic structure. It possesses 92 protons and 92 electrons, making it the heaviest naturally occurring element on the planet. Its density is approximately 19.1 grams per cubic centimeter, which is about 70% higher than that of lead and only slightly less than gold or tungsten. This immense weight allows it to be used in kinetic energy penetrators and armor plating, where its density enables the destruction of heavily armored targets. Despite its heaviness, the metal is malleable and ductile, with a Mohs hardness of 6, which is sufficient to scratch glass. It is also slightly paramagnetic and a poor electrical conductor, yet it reacts with almost all non-metallic elements when heated. The element exists in three allotropic forms, with the gamma form being the most malleable and ductile, stable from 700 degrees Celsius to its melting point. This physical versatility has allowed uranium to be machined and cast into various shapes for industrial and military applications, even though it is weakly radioactive and poses chemical poisoning risks if inhaled or ingested.
The Planet That Named It
The discovery of uranium is credited to the German chemist Martin Heinrich Klaproth, who worked in his experimental laboratory in Berlin in 1789. Klaproth was able to precipitate a yellow compound by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide. He assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder, which he thought was the newly discovered metal itself. In reality, that powder was an oxide of uranium. He named the newly discovered element Uranit after the planet Uranus, which had been discovered eight years earlier by William Herschel. He later renamed it Uranium to conform to the naming standard. The planet Uranus itself was named after the primordial Greek god of the sky. This naming connection marked the beginning of a long history of human interaction with the element, which would eventually lead to the isolation of the metal by Eugène-Melchior Péligot in 1841. Péligot, a Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers in Paris, isolated the first sample of uranium metal by heating uranium tetrachloride with potassium. This isolation was a crucial step that allowed scientists to study the properties of the element in its pure form, leading to further discoveries about its radioactive nature.
The Invisible Rays of Paris
Henri Becquerel discovered radioactivity by using uranium in 1896. Becquerel made the discovery in Paris by leaving a sample of a uranium salt, potassium uranyl sulfate, on top of an unexposed photographic plate in a drawer and noting that the plate had become fogged. He determined that a form of invisible light or rays emitted by uranium had exposed the plate. This discovery was accidental and revolutionary, as it revealed that uranium emitted energy without any external stimulus. The radioactive properties of uranium were thus linked to the element itself, rather than to any external factor. This finding sparked a new field of study and led to the discovery of radium by Marie Curie, who extracted radium from uranium ore. The development of uranium mining to extract radium left a prodigious quantity of uranium as a waste product, since it takes three tonnes of uranium to extract one gram of radium. This waste product was diverted to the glazing industry, making uranium glazes very inexpensive and abundant. Uranium glass and pottery glazes became common, with colors ranging from green to yellow, mauve, black, blue, and red. The discovery of radioactivity also led to the use of uranium in photographic chemicals, lamp filaments for stage lighting bulbs, and even in the leather and wood industries for stains and dyes. The long half-life of uranium-238, which is about 4.47 billion years, made it well-suited for use in estimating the age of the earliest igneous rocks and for other types of radiometric dating.
Who discovered uranium and when was it discovered?
German chemist Martin Heinrich Klaproth discovered uranium in 1789 while working in his experimental laboratory in Berlin. He named the element Uranit after the planet Uranus, which had been discovered eight years earlier by William Herschel. He later renamed it Uranium to conform to the naming standard.
When was uranium metal first isolated and by whom?
Eugène-Melchior Péligot isolated the first sample of uranium metal in 1841. He was a Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers in Paris who isolated the metal by heating uranium tetrachloride with potassium. This isolation allowed scientists to study the properties of the element in its pure form.
What year did Henri Becquerel discover radioactivity using uranium?
Henri Becquerel discovered radioactivity by using uranium in 1896. He made the discovery in Paris by leaving a sample of a uranium salt on top of an unexposed photographic plate in a drawer and noting that the plate had become fogged. This finding revealed that uranium emitted energy without any external stimulus.
When was the first uranium-235 sample separated and by whom?
Alfred O. C. Nier separated the world's first uranium-235 sample on the 29th of February 1940. He used an instrument he built at the University of Minnesota to separate the sample in the Tate Laboratory. John Dunning confirmed the sample to be the isolated fissile material on the 1st of March 1940 using Columbia University's cyclotron.
When and where were the Oklo natural nuclear reactors discovered?
French physicist Francis Perrin discovered fifteen ancient natural nuclear fission reactors in 1972. These reactors are located in three separate ore deposits at the Oklo mine in Gabon, Africa. The ore deposit is 1.7 billion years old and the reactors operated for hundreds of thousands of years.
When did the United States detonate the first uranium-based nuclear weapon in war?
The United States detonated the uranium-based device Little Boy over Hiroshima, Japan on the 6th of August 1945. This event marked the first use of a nuclear weapon in war with a yield equivalent to 12,500 tonnes of TNT. The blast and thermal wave destroyed nearly 50,000 buildings and killed about 75,000 people.
A team led by Enrico Fermi in 1934 found that bombarding uranium with neutrons produces beta rays. The fission products were at first mistaken for new elements with atomic numbers 93 and 94, which the Dean of the Sapienza University of Rome, Orso Mario Corbino, named ausenium and hesperium, respectively. The experiments leading to the discovery of uranium's ability to fission into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann in Hahn's laboratory in Berlin. Lise Meitner and her nephew, physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process nuclear fission. Soon after, Fermi hypothesized that fission of uranium might release enough neutrons to sustain a fission reaction. Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of uranium-235. Fermi urged Alfred O. C. Nier to separate uranium isotopes for determination of the fissile component, and on the 29th of February 1940, Nier used an instrument he built at the University of Minnesota to separate the world's first uranium-235 sample in the Tate Laboratory. Using Columbia University's cyclotron, John Dunning confirmed the sample to be the isolated fissile material on the 1st of March. These discoveries led numerous countries to begin working on the development of nuclear weapons and nuclear power. Despite fission having been discovered in Germany, the Uranverein, Germany's wartime project to research nuclear power and weapons, was hampered by limited resources, infighting, the exile or non-involvement of several prominent scientists in the field, and several crucial mistakes such as failing to account for impurities in available graphite samples which made it appear less suitable as a neutron moderator than it is in reality. Germany's attempts to build a natural uranium heavy water reactor had not come close to reaching criticality by the time the Americans reached Haigerloch, the site of the last German wartime reactor experiment.
The Fire Over Hiroshima
Two types of atomic bomb were developed by the United States during World War II: a uranium-based device codenamed Little Boy whose fissile material was highly enriched uranium, and a plutonium-based device, Fat Man, whose plutonium was derived from uranium-238. Little Boy became the first nuclear weapon used in war when it was detonated over Hiroshima, Japan, on the 6th of August 1945. Exploding with a yield equivalent to 12,500 tonnes of TNT, the blast and thermal wave of the bomb destroyed nearly 50,000 buildings and killed about 75,000 people. In 1943 the Manhattan Project contracted two private companies, Union Carbide and Chevron, to quietly compile a survey of uranium deposits around the world. As the survey results came in, two geology professors studied the results and suggested general guidelines for new sources, including uranium associated with gold mines in the Rand area in South Africa. Initially it was believed that uranium was relatively rare, and that nuclear proliferation could be avoided by simply buying up all known uranium stocks, but within a decade large deposits of it were discovered in many places around the world. The development of nuclear weapons led to an arms race during the Cold War between the United States and the Soviet Union, which produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239. Dismantling of these weapons and related nuclear facilities is carried out within various nuclear disarmament programs and costs billions of dollars. Weapon-grade uranium obtained from nuclear weapons is diluted with uranium-238 and reused as fuel for nuclear reactors. Spent nuclear fuel forms radioactive waste, which mostly consists of uranium-238 and poses a significant health threat and environmental impact.
The Ancient Reactors of Gabon
In 1972, French physicist Francis Perrin discovered fifteen ancient and no longer active natural nuclear fission reactors in three separate ore deposits at the Oklo mine in Gabon, Africa, collectively known as the Oklo Fossil Reactors. The ore deposit is 1.7 billion years old; then, uranium-235 constituted about 3% of uranium on Earth. This is high enough to permit a sustained chain reaction, if other supporting conditions exist. The capacity of the surrounding sediment to contain the health-threatening nuclear waste products has been cited by the U.S. federal government as supporting evidence for the feasibility to store spent nuclear fuel at the Yucca Mountain nuclear waste repository. The existence of such natural fission reactors which had been theoretically predicted beforehand was proven as the slight deviation of uranium-235 concentration from the expected values were discovered during uranium enrichment in France. Subsequent investigations to rule out any nefarious human action confirmed the theory by finding isotope ratios of common fission products in line with the values expected for fission but deviating from the values expected for non-fission derived samples of those elements. This discovery provided a unique window into the past, showing that nuclear reactions could occur naturally under the right conditions. The Oklo reactors operated for hundreds of thousands of years, producing energy and heat in a way that mimics human-made nuclear reactors. The study of these ancient reactors has provided valuable insights into the behavior of nuclear waste and the long-term stability of geological formations.
The Cold War Stockpiles
During the Cold War between the Soviet Union and the United States, huge stockpiles of uranium were amassed and tens of thousands of nuclear weapons were created using enriched uranium and plutonium made from uranium-238. After the break-up of the Soviet Union in 1991, an estimated 600 short tons of highly enriched weapons grade uranium, enough to make 40,000 nuclear warheads, had been stored in often inadequately guarded facilities in the Russian Federation and several other former Soviet states. Police in Asia, Europe, and South America on at least 16 occasions from 1993 to 2005 have intercepted shipments of smuggled bomb-grade uranium or plutonium, most of which was from ex-Soviet sources. From 1993 to 2005 the Material Protection, Control, and Accounting Program, operated by the federal government of the United States, spent about US$550 million to help safeguard uranium and plutonium stockpiles in Russia. This money was used for improvements and security enhancements at research and storage facilities. Safety of nuclear facilities in Russia has been significantly improved since the stabilization of political and economical turmoil of the early 1990s. For example, in 1993 there were 29 incidents ranking above level 1 on the International Nuclear Event Scale, and this number dropped under four per year in 1995 to 2003. The number of employees receiving annual radiation doses above 20 mSv, which is equivalent to a single full-body CT scan, saw a strong decline around 2000. In November 2015, the Russian government approved a federal program for nuclear and radiation safety for 2016 to 2030 with a budget of 562 billion rubles, approximately 8 billion USD. Its key issue is the deferred liabilities accumulated during the 70 years of the nuclear industry, particularly during the time of the Soviet Union. About 73% of the budget will be spent on decommissioning aged and obsolete nuclear reactors and nuclear facilities, especially those involved in state defense programs; 20% will go in processing and disposal of nuclear fuel and radioactive waste, and 5% into monitoring and ensuring of nuclear and radiation safety.
The Green Glass and the Black Dust
Before and after the discovery of radioactivity, uranium was primarily used in small amounts for yellow glass and pottery glazes, such as uranium glass and in Fiestaware. The discovery and isolation of radium in uranium ore by Marie Curie sparked the development of uranium mining to extract the radium, which was used to make glow-in-the-dark paints for clock and aircraft dials. This left a prodigious quantity of uranium as a waste product, since it takes three tonnes of uranium to extract one gram of radium. This waste product was diverted to the glazing industry, making uranium glazes very inexpensive and abundant. Besides the pottery glazes, uranium tile glazes accounted for the bulk of the use, including common bathroom and kitchen tiles which can be produced in green, yellow, mauve, black, blue, red and other colors. Uranium was also used in photographic chemicals, especially uranium nitrate as a toner, in lamp filaments for stage lighting bulbs, to improve the appearance of dentures, and in the leather and wood industries for stains and dyes. Uranium salts are mordants of silk or wool. Uranyl acetate and uranyl formate are used as electron-dense stains in transmission electron microscopy, to increase the contrast of biological specimens in ultrathin sections and in negative staining of viruses, isolated cell organelles and macromolecules. The use of depleted uranium became politically and environmentally contentious after the use of such munitions by the US, UK and other countries during wars in the Persian Gulf and the Balkans raised health questions concerning uranium compounds left in the soil. Uranium miners have a higher incidence of cancer. An excess risk of lung cancer among Navajo uranium miners, for example, has been documented and linked to their occupation. The Radiation Exposure Compensation Act, a 1990 law in the US, required $100,000 in compassion payments to uranium miners diagnosed with cancer or other respiratory ailments.