232Th

232Th is the most stable and abundant isotope of thorium. Its nucleus contains 232 nucleons, composed of 90 protons and 142 neutrons. This isotope is a naturally occurring primordial radionuclide, meaning it has been present on Earth since its formation. The atomic number of 232Th is 90, identifying it as thorium.

232Th is characterized by its extremely long half-life, which is approximately 1.405 × 10^10 years. This long half-life means that a sample of 232Th decays very slowly. It is a member of the thorium decay series, which is one of the four major decay chains of heavy elements. This series begins with 232Th and proceeds through a series of alpha and beta decays, ultimately ending with a stable isotope of lead, 208Pb.

Due to its long half-life and natural abundance, 232Th is present in trace amounts in the Earth's crust, soil, and water. It is also found in some mineral deposits, such as monazite, which is a primary source for thorium extraction. While its radioactivity is low compared to shorter-lived isotopes, its ubiquity means it contributes to the natural background radiation levels. In nuclear applications, 232Th is of interest as a fertile material, meaning it can be converted into fissile isotopes, such as 233U, through neutron absorption.