Thorium

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Thorium (play /ˈθɔəriəm/ THOHR-ee-əm) is a chemical element with the symbol Th and atomic number 90. Thorium is a naturally occurring, slightly radioactive metal. A Thorium atom has 90 protons and 90 electrons, of which 4 are valence electrons. Jöns Jakob Berzelius discovered it in 1828 and named it after Thor, the Norse god of thunder.

In nature, thorium is found as thorium-232 (100.00%). Thorium decays slowly by emitting an alpha particle. The half-life of thorium-232 is about 14.05 billion years. It is estimated to be about three to four times more abundant than uranium in the Earth's crust. It is a by-product of the extraction of rare earths from monazite sands. The formerly widespread uses of thorium, for example as a light emitting material in gas mantles or as an alloying material in several metals, have decreased due to concerns about its radioactivity.

Thorium-232 was used for breeding nuclear fueluranium (233), for example, in the molten-salt reactor experiment (MSR) conducted in the United States from 1964 to 1969. After most of the initial test reactors were closed down, Russia, India and other countries are reconsidering the use of thorium fuel cycle for the production of nuclear power.

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