Thorium

Thorium is a natural radioactive chemical element with the symbol **Th** and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder. In nature, virtually all thorium is found as thorium-232, and it decays by emitting an alpha particle, and has a half-life of about 14.05 billion years (other, trace-level isotopes of thorium are short-lived intermediates of decay chains). It is estimated to be about four times more abundant than uranium in the Earth's crust and is a by-product of the extraction of rare earths from monazite sands. Thorium was formerly used commonly as (for example) the light source in gas mantles and as an alloying material, but these applications have declined due to concerns about its radioactivity. Canada, Germany, India, Netherlands, United Kingdom and the United States have used thorium in various experimental and power reactors as fuel.

232Th+ n ⇒ 233Th ß decay ß decay 233Th ⇒ 233Pa ⇒ 233U Fission of the uranium-233 can provide neutrons to start the cycle again. This cycle of reactions is known as the thorium cycle.
 * Harmful effects: ** Thorium is radioactive. It collects in living animal bones, including human bone, where it can remain for a long period of time.
 * Characteristics: ** Thorium is a radioactive, bright, soft, silvery-white metal, which tarnishes extremely slowly (over many months) to the black oxide. The most stable isotope is thorium-232, with a half-life of 14.05 billion years. Nearly 100% of thorium found on Earth is thorium-232, which is only slightly radioactive because it has such a long half-life. (Uranium-235's half-life is 700 million years, shorter by a factor of 20.) Thorium is chemically reactive and is attacked by oxygen, hydrogen, the halogens and sulfur. Thorium powder is pyrophoric (ignites spontaneously in air). Thorium is dimorphic, changing from face centered cubic to body centered cubic above 1360 oC. Thorium has the largest liquid range of any element, spanning over 3000 degrees between its melting point of 2023 K (1750 oC) and its boiling point of 5063 K (4790 oC). Thorium dioxide (thoria) has the highest melting point of any known oxide. Almost all naturally occurring thorium is thorium-232 which decays slowly to the Group 2 metal radium by emission of alpha particles. Thorium-232 can be converted by thermal (slow) neutrons to fissionable uranium-233 via the following reaction sequence:

Uses of Thorium
An exciting possibility for the future is fueling nuclear reactors with thorium. Not only is thorium more abundant on Earth than uranium, but 1 ton of mined thorium can produce as much energy as 200 tons of mined uranium. (8) The difference in the energy output of the two elements arises because most uranium mined is uranium-238, which is not fissile. (Naturally occurring uranium is over 99% uranium-238 with only about 0.7% of the fissile uranium-235.) Nearly all mined thorium, however, can easily be made into the fissile uranium isotope uranium-233 through neutron bombardment (as shown above).

Waste from a thorium reactor is expected to lose its dangerous radioactivity after about 400-500 years, compared with many thousands of years for nuclear waste produced today. (8) Thorium fuel research is continuing in several countries including the USA and India. (9) Most non-nuclear uses of thorium are driven by the unique properties of its oxide. Thorium dioxide was used in Welsbach gas mantles in the 19th century and today these mantles may still be found in camping lanterns. (Thorium dioxide's very high melting point ensures it stays solid, glowing with an intense, bright white light at the temperature of the lantern's burning gas.) Thorium dioxide is used for heat resistant ceramics. Glass that contains thorium dioxide has a high refractive index and low dispersion, so thorium dioxide is added to glass for use in high quality lenses and scientific equipment. Thorium-magnesium alloys are used in the aerospace industry for aircraft engines. These alloys are lightweight and have excellent strength and creep resistance at high temperatures. Thorium is used to coat tungsten filaments in light bulbs. The demand for thorium in non-nuclear applications is decreasing because of environmental and health concerns due to its radioactivity.

Radioactive Thorium was discovered by Jöns Jacob Berzelius, a Swedish chemist, in 1828. He discovered it in a sample of a mineral that was given to him by the Reverend Has Morten Thrane Esmark, who suspected that it contained an unknown substance. Esmark's mineral is now known as thorite (ThSiO4). Thorium makes up about 0.0007% of the earth's crust and is primarily obtained from thorite, thorianite (ThO2) and monazite ((Ce, La, Th, Nd, Y)PO4). Thorium is used as an alloying agent to improve magnesium's strength at high temperatures. Thorium is also used to coat tungsten filaments used in electronic devices, such at television sets. When bombarded with neutrons, thorium-232 becomes thorium-233, which eventually decays into uranium-233 through a series of beta decays. Uranium-233 is a fissionable material and can be used as a nuclear fuel. Thorium oxide (ThO2), one of thorium's compounds, has many uses. It is primarily used in a type of lantern mantel known as a Welsbach mantle. This mantle, which also contains about 1% cerium oxide, glows with a bright white light when it is heated in a gas flame. Thorium oxide has a very high melting point, about 3300°C, and is used to make high temperature crucibles. Thorium oxide is also used to make glass with a high index of refraction that is used to make high quality camera lenses. Thorium oxide is used as a catalyst in the production of sulfuric acid (H2SO4), in the cracking of petroleum products and in the conversion of ammonia (NH3) to nitric acid (HNO3). Thorium's most stable isotope, thorium-232, has a half-life of about 14,050,000,000 years. It decays into radium-228 through alpha decay or decays through spontaneous fission.
 * Atomic Number:** 90
 * Atomic Weight:** 232.03806
 * Melting Point:** 2023 K (1750°C or 3182°F)
 * Boiling Point:** 5061 K (4788°C or 8650°F)
 * Density:** 11.72 grams per cubic centimeter
 * Phase at Room Temperature:** Solid
 * Element Classification:** Metal
 * Period Number:** 7 **Group Number:** none **Group Name:** Actinide
 * What's in a name?** Named for the Scandinavian god of war, **Thor**.
 * Say what?** Thorium is pronounced as **THOR-ee-em** or as **THO-ree-em**.
 * History and Uses:**


 * Estimated Crustal Abundance:** 9.6 milligrams per kilogram
 * Estimated Oceanic Abundance:** 1×10-6 milligrams per liter
 * Number of Stable Isotopes:** 0
 * Ionization Energy:** 6.08 eV
 * Oxidation State:** +4




 * Date of Discovery:** 1828
 * Discoverer:** Jons Berzelius
 * Name Origin:** Thor (Scandinavian god)
 * Uses:** strong alloys, ultraviolet photoelectric cells
 * Obtained From:** monazite, thorite