Actinium-228 is a radioactive isotope of actinium, a rare earth metal. It is produced through the decay of thorium-232 and has a half-life of about 6.15 hours. This means that after this time, half of a sample of Actinium-228 will have transformed into another element. Actinium-228 emits alpha particles and gamma radiation, making it useful in various applications, including medical treatments and research. Its short half-life limits its use in some areas, but it is still valuable in the study of nuclear physics and the development of targeted therapies for certain diseases.