ETYM New Lat. Related to Thorite.
Dark-gray, radioactive, metallic element of the actinide series, symbol Th, atomic number 90, atomic weight 232.038. It occurs throughout the world in small quantities in minerals such as thorite and is widely distributed in monazite beach sands. It is one of three fissile elements (the others are uranium and plutonium), and its longest-lived isotope has a half-life of 1.39 x 1010 years. Thorium is used to strengthen alloys. It was discovered by Jöns Berzelius 1828 and was named by him after the Norse god Thor.
A soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands; SYN. Th, atomic number 90.