# Uranium

The uranium is a chemical element of symbol U and Atomic number 92.

## Discovered uranium

Uranium was highlighted in 1789 by the Prussian Chimiste Martin Heinrich Klaproth by heating the Pechblende ($UO_2$), a Minerai of uranium. Klaproth gave the name of “uranium oxide” or “uranite” to the compound which it had just identified, in reference to discovered of the planet Uranus made by William Herschel eight years earlier (1781).

They are only fifty years later that the chemist French Eugene Péligot establishes that uranium oxide was composed of two atoms of Oxygène and of one of Métal which it insulated and named uranium.

Henri Becquerel only discovered the property Radioactive of uranium much later, in 1896, when it noted that photographic plates placed beside uranium salts had been impressed without to have been exposed in the light of the sun. The plates had been blackened by the radiations emitted by salts: the French Henri Becquerel had discovered the phenomenon of the natural Radioactivité.

## Characteristics

Of symbol U uranium is the last element Naturel of the periodic Tableau of Mendeleïev. Each Atome of uranium has 92 Proton S and between 135 and 148 Neutron S.

In a pure state, solid uranium is a Métal Radioactif gray with white (even silver plated), which points out the color of the Nickel. It is hard and very Dense. Moreover, uranium is the heaviest atom (which contains the most Nucléon S) present naturally on the Ground.

### Natural uranium

Natural uranium is present in practically all the natural environments: rocks and Water. There is indeed 3  uranium Mg per cubic meter of sea water, which represents 4,5  all the same; billion tons of uranium in the oceans!
uranium is really present in all the types of water: the the Rhone carts some indeed close to 100  tons each year. This uranium comes from the streaming of the rains on the the Alps. The extraction of the uranium of water is, technically possible, but nonprofitable in 2006.

Uranium is relatively widespread all the same in the Earth's crust, in particular in the grounds granitic S and Sédimentaire S. the uranium concentration in these rocks is about 3  g/tonne. As example, a square garden of 20  m on side contains, for a depth of 10  m, approximately 24  kg of uranium.

#### Other chemical properties

Because of its affinity for oxygen, uranium ignites spontaneously in the air with high temperature, even with room temperature when it is in the form of microparticles.

Moreover, the element uranium always finds in combination with other elements the such Oxygène, the Azote, the Soufre, the Carbone. One finds it for example in combination with oxygen in the Uranite and the Pechblende, two of the principal ores of uranium, consisted of uranous oxide ($UO_2$).

Lastly, the ions uranyls ($UO_2^ \left\{2+\right\}$) dissolve very well in the majority of the Acide S, as in the nitric Acid or hydrofluoric by giving uranyl salts such as the uranyl nitrate. The equation of the dissolution of the ion uranyl out of salt uranyl in the nitric acid is the following one:

$UO_2^ \left\{2+\right\} + 2NO_3^- \ longrightarrow UO_2 \left(NO_3\right) _2$

#### Radioactivity - One of the origins of heat interns Earth

At the time geological current, the Chaleur intern of the Earth comes mainly from the disintegration of radioactive bodies, in particular uranium 238 and 235 (and well of others). This can be explained in a relatively simple way: during their radioactive decay, uranium 238 and Uranium 235 will emit radiations $\ gamma$, which are energy in a pure state. Billion billion de-energizings $\ gamma$ takes place each second inside the Earth, this energy is then converted into heat. This reasoning is also valid for the other types of radioactivity, from which the energy of the emitted particle is transferred to the close atoms.
One includes/understands easily why the radioactivity is at the origin of almost 87% of the thermal energy of the Earth.

#### Isotopes of natural uranium

Uranium has seventeen Isotope S, all Radioactif S, of which three only are present at the natural state: 238 U; 235 U and 234 U.

Whatever the uranium contents of the mediums, the proportions between the three isotopes forming natural uranium are (almost) exactly the same ones: 238U: 99,28%; 235U: 0,71%; 234U: 0,0054%.

One thus finds in a ton of pure natural uranium 7,1 kilograms of U235 and 54 grams of U234, the remainder being of U238. Isotope 234 is always present on Earth, with the state of traces, although it has a half-life of only: 245500 years, because it is constantly generated by isotope 238 (after 3 radioactivities: α, $\ beta-$, $\ beta-$).

Isotope 236 died out for a long time, although having a half-life almost centuple.

### Natural fissionable product

Uranium 235 is only the natural Nucléide which is Fissile, or Fissible: it is thus likely to undergo nuclear fission.

Contrary to Uranium 235, uranium 238, when it captures a Neutron, does not fission (except fast neutrons). It becomes uranium 239 unstable, which by Désintégration $\ beta-$, will be transformed into Neptunium 239. However this last is him-also Radioactif $\ beta-$, and then will give rise to new a core, the Plutonium 239. This Radioisotope is fissile, like Uranium 235. Uranium 238 is a fertile Isotope, which can produce fissile products.

Uranium 234 is him neither fissile, nor fertile, and comes from the radioactive Décomposition of uranium 238.

## Use

In the beginning, the uranium ore was used in the Céramique and the Faïence for its pigments yellow, orange and green

Uraniums 238 and 235 have many applications, soldiers in particular, but so civil such as for example the dating of the age of the Earth starting from the radiometric Datation.

### Control nuclear matters

Uranium is a nuclear matter whose detention is regulated (R1333-1 Article of the code of defense).

### Nuclear fuel

Uranium is today used like Fuel nuclear in the nuclear reactors (see Cycle of nuclear fuel).

### Nuclear weapons

The uranium enriched (out of Uranium 235) can also be used with the realization as nuclear weapons as the atomic bombs (bombs has or “bombs with fission”), or the H-bombs (“bombs with fusion” or “hydrogen bombs”).

### Depleted uranium

The Uranium depleted, under product of the Uranium enrichment, is very snuffed for its Dureté and its Densité. Moreover, it is Pyrophorique and it is thus employed as arms anti-tank having a strong capacity penetrating and flamer. At very high-speed, it easily perforates the shieldings while igniting at the time of the impact, causing a fire which explodes the vehicle concerned. Thus, of the ammunition containing depleted uranium (shell from 20 to 30 mm of the planes or helicopters tank destroyers) were used at the time of the wars of the Gulf (war of Kuwait and war in Iraq) and of the Kosovo.

The depleted uranium is also used, with a complement of Plutonium, like new Fuel nuclear (Combustible MOX).

However, the depleted uranium can produce, at short distance, same radiations as a nuclear Explosion (?) and to cause serious problems on the human body.