Thorium-228 is a radioactive isotope of thorium, a naturally occurring element. It has a half-life of about 1.91 years and is produced from the decay of uranium-232. Thorium-228 is part of the thorium decay series, which eventually leads to stable lead isotopes. This isotope emits alpha particles during its decay process, making it useful in certain applications, such as in radiopharmaceuticals for medical imaging. Additionally, thorium-228 can be used in research related to nuclear energy, as thorium is considered a potential alternative to conventional nuclear fuels.