Facts About Thorium | Live Science

Thorium, named after the Norse god of thunder, is a silvery, shiny and radioactive element with potential as an alternative to uranium in the fueling of nuclear reactors.

Just the facts

  • Atomic number (number of protons in the nucleus): 90
  • Atomic symbol (in the periodic table of the elements): Th
  • Atomic weight (average mass of the atom): 232.0
  • Density: 6.8 ounces per cubic inch (11.7 grams per cubic centimeter)
  • Phase at room temperature: solid
  • Melting point: 3,182 degrees Fahrenheit (1,750 degrees Celsius)
  • Boiling point: 8,654 F (4,790 ° C)
  • Number of natural isotopes (atoms of the same element with different numbers of neutrons): 1. At least 8 radioactive isotopes are produced in a laboratory.
  • Most common isotopes: Th-232 (100 percent of natural abundance)

Atomic information and electron configuration of thorium (Photo credit: Andrei Marincas / Shutterstock; BlueRingMedia / Shutterstock)


In 1815 the Swedish chemist Jöns Jakob Berzelius believed for the first time that he had discovered a new earth element, which he named thorium after Peter, the Nordic god of war, after Peter van der Krogt, a Dutch historian. However, in 1824 it was found that the mineral was actually yttrium phosphate;

In 1828 Berzelius received a sample of a black mineral from Hans Morten Thrane Esmark, a Norwegian mineralogist, that was found on the island of Løvø off the coast of Norway. The mineral contained nearly 60 percent of an unknown element that took the name thorium; The mineral was called thorite. The mineral also contained many familiar elements, including iron, manganese, lead, tin, and uranium, according to Chemicool.

Berzelius isolated thorium by first mixing the thorium oxide found in the mineral with carbon to produce thorium chloride, which, according to Chemicool, was then reacted with potassium to form thorium and potassium chloride.

Gerhard Schmidt, a German chemist, and Marie Curie, a Polish physicist, independently discovered, according to Chemicool, that thorium was radioactive within a few months of each other in 1898. The discovery is often attributed to Schmidt.

Ernest Rutherford, a New Zealand physicist, and Frederick Soddy, an English chemist, discovered that thorium decays at a fixed rate into other elements, also known as an element’s half-life, according to Los Alamos National Laboratory. This work was critical to understanding other radioactive elements.

Anton Eduard van Arkel and Jan Handrik de Boer, both Dutch chemists, isolated high-purity metallic thorium in 1925, according to Los Alamos National Laboratory.

Who knew

  • In its liquid state, according to Chemicool, thorium has a larger temperature range than any other element, with almost 3,000 degrees Celsius between the melting point and boiling point.
  • According to Chemicool, thorium dioxide has the highest melting point of all known oxides.
  • According to Lenntech, thorium is about as common as lead and at least three times as common as uranium.
  • According to Chemicool, the amount of thorium in the earth’s crust is 6 parts by weight per million. According to the periodic table, thorium is the 41st most abundant element in the earth’s crust.
  • According to the Minerals Education Coalition, thorium is primarily mined in Australia, Canada, the United States, Russia, and India.
  • According to the US Environmental Protection Agency (EPA), traces of thorium can be found in rocks, soil, water, plants and animals.
  • According to Los Alamos National Laboratory, minerals such as thorite, thorianite, monazite, allanite, and zirconia typically have higher concentrations of thorium.
  • The most stable isotope of thorium, Th-232, has a half-life of 14 billion years, according to the EPA.
  • According to Los Alamos, thorium is created in the cores of supernovae and then scattered across the galaxy during the explosions.
  • According to Los Alamos, thorium has been used in gas jackets that provide the light in gas lamps since 1885. Due to its radioactivity, the element has been replaced by other non-radioactive rare earth elements.
  • Thorium is also used to reinforce magnesium, coat tungsten wire in electrical equipment, control the grain size of tungsten in electric lamps, high temperature crucibles, in glasses, in camera and scientific instrument lenses, and is according to Los Alamos.
  • Other uses for thorium include refractory ceramics, aircraft engines, and light bulbs, according to Chemicool.
  • According to Lenntech, thorium was used in toothpaste until radioactivity hazards were discovered.
  • According to the Minerals Education Coalition, thorium and uranium are involved in warming the Earth’s interior.
  • Excessive thorium exposure can lead to lung disease, lung and pancreatic cancer, changes in genetics, liver disease, bone cancer and metal poisoning, according to Lenntech.

Current research

Much research is being done into the use of thorium as a nuclear fuel. According to an article by the Royal Society of Chemistry, thorium, used in nuclear reactors, offers many advantages over using uranium:

  • Thorium is three to four times more common than uranium.
  • Thorium is easier to extract than uranium.
  • Liquid fluoride thorium reactors (LFTR) have very little waste compared to uranium fueled reactors.
  • LFTRs run at atmospheric pressure instead of 150 to 160 times atmospheric pressure currently required.
  • Thorium is less radioactive than uranium.

According to a 2009 publication by NASA researchers Albert J. Juhasz, Richard A. Rarick, and Rajmohan Rangarajan, thorium reactors were developed to support nuclear aircraft programs at Oak Ridge National Laboratory under the direction of Alvin Weinberg in the 1950s. The program was discontinued in 1961 in favor of other technologies. According to the Royal Society of Chemistry, thorium reactors were abandoned because they didn’t produce as much plutonium as uranium-powered reactors. At that time, weapons-grade plutonium and uranium were hot commodities due to the Cold War.

Thorium itself is not used as a nuclear fuel, but it is used to make the man-made isotope of uranium, uranium-233, according to the NASA report. Thorium-232 first absorbs a neutron and produces thorium-233, which decays to protactium-233 within about four hours. Protactium-233 slowly decays into uranium-233 over a period of about ten months. Uranium-233 is then used as fuel in nuclear reactors.

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