Thorium

General properties
Name, symbol, number	thorium, Th, 90
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	232.03806
Electron configuration	[Rn] 6d2 7s2 2, 8, 18, 32, 18, 10, 2
History
Discovery	Jöns Jakob Berzelius (1829)

Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder.

In nature, virtually all thorium is found as thorium-232, which undergoes alpha decay with a half-life of about 14.05 billion years. Other isotopes of thorium are short-lived intermediates in the decay chains of higher elements, and only found in trace amounts. Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals.

Thorium was once commonly used as the light source in gas mantles and as an alloying material, but these applications have declined due to concerns about its radioactivity. Thorium is also used as an alloying element in nonconsumable TIG welding electrodes.

Canada, Germany, India, the Netherlands, the United Kingdom and the United States have experimented with using thorium as a substitute nuclear fuel in nuclear reactors. There is a growing interest in developing a thorium fuel cycle due to its safety benefits, absence of non-fertile isotopes, and its higher occurrence and availability when compared to uranium. India's three stage nuclear power programme is possibly the most well known and well funded of such efforts.

Return to Periodic Table