Ураниум

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Ураниум е хемиски елемент со симбол U и атомски број 92. Тој е сребрено-бел метал во актинидите во периодниот систем. Во составот на атомот на ураниумот има 92 протони и 92 електрони , од кои 6 се валентни електрони. Ураниумот е слабо радиоактивен затоа што сите негови изотопи се нестабилни. Најчестите изотопи во природниот ураниум се ураниум-238 (кој има 146 неутрони) и ураниум-235 (кој има 143 неутрони). Ураниумот има втора највисока атомска маса од примордалните нуклиди кои се јавувачки елементи, полесни само од плутониум.[1] Неговата густина е одприлика 70% повисока од густината на оловото, и малку пониска од густината на златото или волфрамот. Тоа се појавува во ниски концентрации во почвата , камењата и водата , и е извлечена од ураниумски минерали како штo е уранитот.

Во природата, ураниумот се пронаоѓа како ураниум-238 (99.2739–99.2752%), ураниум-235 (0.7198–0.7202%), и една мала количина од ураниум-234 (0.0050–0.0059%).[2] Ураниумот се распаѓа полека со емитација на алфа честички. Полу-животот на ураниум-238 е скоро 4.47 билион години а на ураниум-235 е 704 милион години,[3] што ги прави корисни за да се дознае староста на Земјата.

Во 1789 откритието на ураниумот во минералот pitchblende се препишува на Martin Heinrich Klaproth, кој го крстил новиот елемент по планетата Уранус. Eugène-Melchior Péligot е првиот човек кој изолирал метал и неговите радиоактивни особини се откриени во 1896 од Henri Becquerel. Истражувањето од страна на Otto Hahn, Lise Meitner, Enrico Fermi и останати научници, како J. Robert Oppenheimer довело во 1934 употреба на неговото гориво во нуклеарната а исто така и во Little Boy, првото нуклеарно оружје искористено во војна.

Карактеристики[уреди | уреди извор]

A diagram showing a chain transformation of uranium-235 to uranium-236 to barium-141 and krypton-92
Индуциран неутрон предизвикан од нуклеарна фисија вклучувајќи ураниум-235

Кога е рефиниран(префинет), ураниумот е сребрено бел, слабо радиоактивен метал. Има Мохсова цврстина од 6, доволно да скрши стакло и приближно еднаква цврстина со цврстината на титаниумот, родиумот, манганот и ниобиумот. Тој е податлив, нодуларен, малку парамагнетичен, силно електропозитивен и слаб електричен кондуктор(донор).[4][5] Ураниум металот има многу висока густина од 19.1 g/cm3,[6] denser than lead (11.3 g/cm3),[7] но помала густина од волфрам и злато (19.3 g/cm3).[8][9]

Ураниум металот стапува во реакција со речиси сите не-метални елементи (со исклучок на благородните гасови и нивните соединенија, со реактивност која се зголемува со температура.[10] Хлороводородната и азотната киселина го раствараат ураниумот, но не-оксидираните киселини освен хлороводородните киселини го напаѓаат елементот многу споро.[4] Кога се ситно поделени, може да реагираат со ладна вода; во вода, ураниум металот е обложен со темен слој од ураниум оксид.[5] Ураниум рудата е извлечена хемиски и претворена во ураниум диоксид или други хемиски форми корисни во индустријата.

Ураниум-235 е првиот изотоп кој бил пронајден како фисил. Други природни изотопи се фисионарни, но не фисилни. Со бомбардирање со спори неутрони, неговите ураниум-235 изотопи во поголемиот дел од времето ке се поделат во две мали јадра, испуштајќи нуклеарна обврзувачка енергија и повеќе неутрони. Ако премногу од овие неутрони се апсорбираат од друг ураниум-235 јадра, на нуклеарната верижна реакција се случува дека резултатите се во излив на топлина или (во специјални околности) доаѓа до експлозија. Во нуклеарен реактор, верижната реакција е успорена и контролирана од страна на неутронски отров, одбивајќи некои од слободните неутрони. Таквите неутронски абсорбни материјали се често дел од реактори контролни печки.

Со само 15 lb (7 kg) од ураниум-235 може да се создаде атомска бомба.[11] Првата нуклеарна бомба искористена во војна е Little Boy(Мало Момче), која е направена од ураниумска фисија, но првиот нуклеарен експлозив (Gadget е искористен во Trinity) и бомбата која го уништи Нагасаки (Fat Man(Дебел Човек)) биле двете пуноиум бомби.

Ураниум металот има три алотропни форми allotropic forms:[12]

Апликации[уреди | уреди извор]

Воена корист[уреди | уреди извор]

Shiny metallic cylinder with a sharpened tip. The overall length is 9 cm and diameter about 2 cm.
Многу војски користат осиромашен ураниум како високо-густински пенетратори.

Главната примена на ураниумот во воениот сектор е во високо-густинскиот пенетратор. Оваа муниција се состои од осиромашен ураниум легирани со 1–2% други елементи, како што се титаниумот или молибденот.[14] Со големо влијание на брзината, густината, цврстината, и спонтано палење на проектилот, овозможува уништување на тешко оклопни цели. Тенк оклопот и други остранливи возачки оклопи можат исто така да бидат зацврстени со осиромашени ураниумски таблици. Употребата на осиромашен ураниум стана политички и еколошки спорен после користењето на таа муниција од страна на САД, Велика Британија и други земји за време на војната во Персискиот Залив и на Балканот било поткренато прашање во врска со соединенијата на ураниум оставени во почвата (види Gulf War Syndrome).[11]

Осиромашениот ураниум исто така се користи како заштитен материјал за некои садови кои се користат за чување и транспорт на радиоактивни материјали. While the metal itself is radioactive, its high density makes it more effective than lead in halting radiation from strong sources such as radium.[4] Other uses of depleted uranium include counterweights for aircraft control surfaces, as ballast for missile re-entry vehicles and as a shielding material.[5] Due to its high density, this material is found in inertial guidance systems and in gyroscopic compasses.[5] Depleted uranium is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost.[15] The main risk of exposure to depleted uranium is chemical poisoning by uranium oxide rather than radioactivity (uranium being only a weak alpha emitter).

During the later stages of World War II, the entire Cold War, and to a lesser extent afterwards, uranium-235 has been used as the fissile explosive material to produce nuclear weapons. Initially, two major types of fission bombs were built: a relatively simple device that uses uranium-235 and a more complicated mechanism that uses plutonium-239 derived from uranium-238. Later, a much more complicated and far more powerful type of fission/fusion bomb (thermonuclear weapon) was built, that uses a plutonium-based device to cause a mixture of tritium and deuterium to undergo nuclear fusion. Such bombs are jacketed in a non-fissile (unenriched) uranium case, and they derive more than half their power from the fission of this material by fast neutrons from the nuclear fusion process.[16]

Civilian[уреди | уреди извор]

Photograph featuring sunflowers in front and a plant on the back. The plant has a wide smoking chimney with diameter comparable to its height.
The most visible civilian use of uranium is as the thermal power source used in nuclear power plants

The main use of uranium in the civilian sector is to fuel nuclear power plants. One kilogram of uranium-235 can theoretically produce about 20 terajoules of energy (2×1013 joules), assuming complete fission; as much energy as 1500 tonnes of coal.[17]

Commercial nuclear power plants use fuel that is typically enriched to around 3% uranium-235.[17] The CANDU and Magnox designs are the only commercial reactors capable of using unenriched uranium fuel. Fuel used for United States Navy reactors is typically highly enriched in uranium-235 (the exact values are classified). In a breeder reactor, uranium-238 can also be converted into plutonium through the following reaction:[5]

[[Шаблон:LinkForElement|238
92
U]]
+ n [[Шаблон:LinkForElement|239
92
U]]
+ γ [[Шаблон:LinkForElement|239
93
Np]]
[[Шаблон:LinkForElement|239
94
Pu]]
A glass place on a glass stand. The plate is glowing green while the stand is colorless.
Uranium glass glowing under UV light

Before (and, occasionally, 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.[18]

The discovery and isolation of radium in uranium ore (pitchblende) 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.[19] 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.

A glass cylinder capped on both ends with metal electrodes. Inside the glass bulb there is a metal cylinder connected to the electrodes.
Uranium glass used as lead-in seals in a vacuum capacitor

Uranium was also used in photographic chemicals (especially uranium nitrate as a toner),[5] in lamp filaments for stage lighting bulbs,[20] to improve the appearance of dentures,[21] 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 discovery of the radioactivity of uranium ushered in additional scientific and practical uses of the element. The long half-life of the isotope uranium-238 (4.51×109 years) makes it well-suited for use in estimating the age of the earliest igneous rocks and for other types of radiometric dating, including uranium-thorium dating, uranium-lead dating and uranium-uranium dating. Uranium metal is used for X-ray targets in the making of high-energy X-rays.[5]

History[уреди | уреди извор]

Pre-discovery use[уреди | уреди извор]

The planet Uranus, which uranium is named after

The use of uranium in its natural oxide form dates back to at least the year 79 CE, when it was used to add a yellow color to ceramic glazes.[5] Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy, by R. T. Gunther of the University of Oxford in 1912.[22] Starting in the late Middle Ages, pitchblende was extracted from the Habsburg silver mines in Joachimsthal, Bohemia (now Jáchymov in the Czech Republic), and was used as a coloring agent in the local glassmaking industry.[23] In the early 19th century, the world's only known sources of uranium ore were these mines.

Discovery[уреди | уреди извор]

Two fuzzy black features on a fuzzy white paper-like background. There is a handwriting at the top of the picture.
Antoine Henri Becquerel discovered the phenomenon of radioactivity by exposing a photographic plate to uranium in 1896

The discovery of the element is credited to the German chemist Martin Heinrich Klaproth. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide.[23] Klaproth 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 fact, that powder was an oxide of uranium).[23][24] He named the newly discovered element after the planet Uranus, (named after the primordial Greek god of the sky), which had been discovered eight years earlier by William Herschel.[25]

In 1841, Eugène-Melchior Péligot, Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers (Central School of Arts and Manufactures) in Paris, isolated the first sample of uranium metal by heating uranium tetrachloride with potassium.[23][26]

Henri Becquerel discovered radioactivity by using uranium in 1896.[10] Becquerel made the discovery in Paris by leaving a sample of a uranium salt, K2UO2(SO4)2 (potassium uranyl sulfate), on top of an unexposed photographic plate in a drawer and noting that the plate had become "fogged".[27] He determined that a form of invisible light or rays emitted by uranium had exposed the plate.

Fission research[уреди | уреди извор]

Cubes and cuboids of uranium produced during the Manhattan project

A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays (electrons or positrons from the elements produced; see beta particle).[28] The fission products were at first mistaken for new elements of atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ausonium and hesperium, respectively.[29][30][31][32] The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann[28] in Hahn's laboratory in Berlin. Lise Meitner and her nephew, the physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process "nuclear fission".[33] Soon after, Fermi hypothesized that the 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 the rare uranium isotope uranium-235.[28] Further work found that the far more common uranium-238 isotope can be transmuted into plutonium, which, like uranium-235, is also fissile by thermal neutrons. These discoveries led numerous countries to begin working on the development of nuclear weapons and nuclear power.

On 2 December 1942, as part of the Manhattan Project, another team led by Enrico Fermi was able to initiate the first artificial self-sustained nuclear chain reaction, Chicago Pile-1. Working in a lab below the stands of Stagg Field at the University of Chicago, the team created the conditions needed for such a reaction by piling together 400 short tons (360 metric tons) of graphite, 58 short tons (53 metric tons) of uranium oxide, and six short tons (5.5 metric tons) of uranium metal, a majority of which was supplied by Westinghouse Lamp Plant in a makeshift production process.[28][34]

Nuclear weaponry[уреди | уреди извор]

White fragmentred mushroom-like smoke cloud evolving from the ground.
The mushroom cloud over Hiroshima after the dropping of the uranium-based atomic bomb nicknamed 'Little Boy'

Two major types of atomic bombs 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 (see Trinity test and "Fat Man") whose plutonium was derived from uranium-238. The uranium-based Little Boy device became the first nuclear weapon used in war when it was detonated over the Japanese city of Hiroshima on 6 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 approximately 75,000 people (see Atomic bombings of Hiroshima and Nagasaki).[27] 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.[35]

Reactors[уреди | уреди извор]

An industrial room with four large illuminated light bulbs hanging down from a bar.
Four light bulbs lit with electricity generated from the first artificial electricity-producing nuclear reactor, EBR-I (1951)

The X-10 Graphite Reactor at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, formerly known as the Clinton Pile and X-10 Pile, was the world's second artificial nuclear reactor (after Enrico Fermi's Chicago Pile) and was the first reactor designed and built for continuous operation. Argonne National Laboratory's Experimental Breeder Reactor I, located at the Atomic Energy Commission's National Reactor Testing Station near Arco, Idaho, became the first nuclear reactor to create electricity on 20 December 1951.[36] Initially, four 150-watt light bulbs were lit by the reactor, but improvements eventually enabled it to power the whole facility (later, the town of Arco became the first in the world to have all its electricity come from nuclear power generated by BORAX-III, another reactor designed and operated by Argonne National Laboratory).[37][38] The world's first commercial scale nuclear power station, Obninsk in the Soviet Union, began generation with its reactor AM-1 on 27 June 1954. Other early nuclear power plants were Calder Hall in England, which began generation on 17 October 1956,[39] and the Shippingport Atomic Power Station in Pennsylvania, which began on 26 May 1958. Nuclear power was used for the first time for propulsion by a submarine, the USS Nautilus, in 1954.[28][40]

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