The thorium decay series begins with the radioactive isotope thorium-232. As it decays, it transforms into a series of other radioactive elements, including radium-228 and lead-208. This process occurs through a sequence of alpha and beta decays, ultimately leading to stable isotopes. Each step in the decay series releases energy in the form of radiation. The entire series can take thousands of years to complete, with each isotope having its own half-life. Understanding the thorium decay series is important for applications in nuclear energy and radiation safety.