Thorium is a naturally-occurring chemical element with atomic number 90 which means there are 90 protons and 90 electrons in the atomic structure. The chemical symbol for thorium is Th. Thorium was discovered in 1828 by norwegian mineralogist Morten Thrane Esmark. Joens Jakob Berzelius, the swedish chemist, named it after Thor, the Norse god of thunder.
Thorium is a naturally-occurring element and it is estimated to be about three times more abundant than uranium. Thorium is commonly found in monazite sands (rare earth metals containing phosphate mineral).
Thorium has 6 naturally occurring isotopes. All of these isotopes are unstable (radioactive), but only 232Th is relatively stable with half-life of 14 billion years, which is comparable to the age of the Earth (~4.5×109 years). Isotope 232Th belongs to primordial nuclides and natural thorium consists primarily of isotope 232Th. Other isotopes (230Th, 229Th, 228Th, 234Th and 227Th) occur in nature as trace radioisotopes, which originate from decay of 232Th, 235U and 238U.