What is Uranium?
Physical and chemical properties, origin, and uses of uranium.
Properties of Uranium
Uranium is a radioactive element that occurs naturally in varying but small amounts in soil, rocks, water, plants, animals and all human beings. It is the heaviest naturally occurring element, with an atomic number of 92. In its pure form, uranium is a silver-colored heavy metal that is nearly twice as dense as lead. In nature, uranium atoms exist as several isotopes, which are identified by the total number of protons and neutrons in the nucleus: uranium-238, uranium-235, and uranium-234. (Isotopes of an element have the same number of protons in the nucleus, but a different number of neutrons.) In a typical sample of natural uranium, most of the weight (99.27%) consists of atoms of uranium-238. About 0.72% of the weight consists of atoms of uranium-235, and a very small amount (0.0055% by weight) is uranium-234.
Radioactive Isotopes of Uranium
The three naturally occurring isotopes of uranium are each radioactive, which means the nuclei spontaneously disintegrate or "decay." Radioactivity emitted from uranium isotopes consists of alpha particles (a collection of two protons and two neutrons) and gamma rays (an electromagnetic energy wave similar to visible light except with higher energy and more penetrating power). The rate at which the nuclei in an isotope sample decay is called activity, which is the number of disintegrations that occur per second. The activity of an isotope sample decreases with time as the atoms disintegrate. Each isotope has its own half-life, which is the time it takes for half of the atoms in a sample of the isotope to decay and the activity of the sample to be proportionately reduced.
Uranium-235 and Fission
In addition to being naturally radioactive, the uranium-235 isotope of uranium is capable of fission, the splitting of the nucleus into two parts, triggered by absorption of a neutron. When this splitting occurs, considerable energy is released, which makes uranium-235 valuable as a fuel in nuclear reactors used to generate electricity and for use in U.S. National Defense.
Historic and Present Uses of Uranium
For many years, uranium was used primarily as a colorant in ceramic glazes, producing colors that ranged from orange-red to lemon yellow. It was also used for tinting in early photography. Its radioactive properties were not recognized until 1896, and its potential for use as an energy source was not realized until the middle of the 20th century. Its primary use is as fuel in nuclear power reactors to generate electricity. It is also used in weapons applications, and in small nuclear reactors to produce isotopes for medical and industrial purposes around the world.
Origin of Uranium
Small amounts of uranium are found almost everywhere in soil, rock, and water. However, concentrated deposits of uranium ores are found in just a few places, usually in hard rock or sandstone. These deposits are normally covered over with earth and vegetation. Uranium has been mined in Canada, the southwest United States, Australia, parts of Europe, the former Soviet Union, Namibia, South Africa, Niger and elsewhere.