Thorium isotopes are variants of the chemical element thorium, which has an atomic number of 90. The most common isotope, thorium-232, is naturally occurring and has a long half-life of about 14 billion years. It is primarily used in nuclear reactors and research due to its ability to absorb neutrons and convert into uranium-233, a fissile material. Other isotopes of thorium, such as thorium-230 and thorium-228, are radioactive and have shorter half-lives. These isotopes are produced through the decay of uranium and are used in various applications, including dating geological formations and studying environmental processes.