Thorium

Thorium was discovered in 1828 by the Swedish chemist Jons Jacob Berzelius, in a black mineral sent to him from Norway by the mineralogist Morten Thrane Esmark. Berzelius named it after Thor, the Norse god of thunder. Its radioactivity was demonstrated in 1898, by Gerhard Carl Schmidt and, independently, Marie Curie. Thorium is a dense, silvery, weakly radioactive metal, once widely used in incandescent gas mantles and long studied as a potential fuel for nuclear reactors. Several times more abundant than uranium in the crust, thorium once brightened the mantles of gas lamps and stiffened optical glass, and its capacity to breed nuclear fuel keeps it under study as the basis of a potentially safer and more plentiful reactor cycle.

India has pursued thorium reactor research more seriously than most nations, since its coastal monazite sands hold some of the world's largest thorium reserves relative to its comparatively modest uranium deposits, and its long-term nuclear programme has explicitly planned around an eventual thorium fuel cycle since the 1950s. Earlier, the United States ran a molten-salt reactor at Oak Ridge National Laboratory through the 1960s specifically to test thorium as a fuel, a promising demonstration ultimately abandoned when Cold War strategic priorities favoured uranium and plutonium reactor designs capable of also producing weapons material.

Berzelius reached, as several Scandinavian chemists did, into Norse rather than classical mythology, naming his new element after Thor, the hammer-wielding god of thunder, storms and strength, one of the mightiest figures of the Norse pantheon and the protector of gods and men. The choice pairs thorium with vanadium, named for the goddess Vanadis, as the periodic table's principal tributes to the old gods of the north. The naming was purely honorific, made before thorium's radioactivity or its latent nuclear energy were even suspected, yet it acquired a fitting resonance in the atomic age, when the thunder-god's element was proposed as the fuel of a safer kind of reactor. Its abundance in the Earth's crust keeps that promise alive in ongoing research.

Thorium-impregnated gas mantles, once standard in camping lanterns and gas lighting fixtures, are mildly radioactive, and although the health risk from any single mantle is small, growing regulatory caution led most manufacturers to phase out thoriated mantles in favour of yttrium-based alternatives by the late twentieth century, a quiet substitution most users of camping equipment never noticed. Older thoriated mantles are still sought by some collectors and Geiger-counter hobbyists specifically because of their easily detectable radioactivity.