Background | Name | Sources | Uses | Substitutes and Alternative Sources Background
Thorium is a silver-gray, radioactive, metallic element. Its atomic number is 90 and its symbol is Th. It was discovered in 1829 by the Swedish chemist Jöns Jakob Berzelius. It is the most common of a group of elements called the actinides. It is the 39th most abundant element in the Earth’s crust at 7.2 parts per million (ppm). Other elements in the actinide group are the natural elements uranium and plutonium. However, most of the actinide elements are not naturally occurring and have the atomic numbers from 89, actinium, through 103, lawrencium.
It is also radioactive. The radioactive breakdown of uranium and thorium create the energy that heats the interior of the Earth. Based on the estimates of the abundance of thorium in the Earth’s crust, there is more energy in thorium than in the fossil fuels and uranium combined! In the 1980’s, 45 tons of thorium was used every year. However, it is used less and less because of the state and federal laws about the handling, transportation and disposal of radioactive materials. Its use will most likely continue to decline unless less expensive methods of disposal are developed.
The principal isotope of thorium has a half-life of 14,000,000,000 years.
Thorium and uranium are the only two actinide elements that are found in large enough quantities to mine. Thorium is found in the minerals monazite (rare earth-thorium phosphate) and thorianite (thorium dioxide).