Thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. The most stable isotope, 232Th, has a half-life of 14. 05 billion years, or about the age of the universe. Thorium was discovered in 1828 by the Norwegian amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jacob Berzelius.