thorium232n

Thorium-232 (often written as $^{232}$Th or simply Th-232) is a naturally occurring isotope of thorium. It is the only isotope of thorium found in significant quantities in nature. Thorium-232 is a radioactive element with a very long half-life of approximately 1.405 × 10^10 years. This extremely long half-life means that its decay rate is very slow, and it is considered a primordial radionuclide, meaning it has existed since the formation of the Earth.

The decay chain of thorium-232 is a series of radioactive transformations that eventually leads to a stable isotope of lead, lead-208 ($^{208}$Pb). The initial decay of thorium-232 is via alpha emission to radium-228 ($^{228}$Ra). Radium-228 then undergoes beta decay to actinium-228 ($^{228}$Ac), which in turn decays by beta emission to thorium-228 ($^{228}$Th). This branching point leads to further decays, including alpha and beta emissions, through a number of intermediate isotopes such as radium-224 ($^{224}$Ra), radon-220 ($^{220}$Rn), polonium-216 ($^{216}$Po), lead-212 ($^{212}$Pb), and bismuth-212 ($^{212}$Bi), before finally reaching the stable endpoint of lead-208.

Thorium-232 is a significant component of the Earth's crust. Its natural occurrence is the source of background radiation in many environments. Due to its long half-life and the presence of its decay products, it contributes to the natural radioactivity measured in soil, rocks, and water. While thorium itself is not highly mobile in the environment, its decay products, particularly radon gas, can be released and pose potential health concerns if accumulated in enclosed spaces. Research has explored its potential use as a nuclear fuel, particularly in thorium fuel cycles, due to its abundance and the fact that it is fertile rather than fissile.