Actinium-228 is a radioactive isotope of the element actinium, which has the atomic number 89. It is produced through the decay of thorium-232 and is part of the uranium-232 decay series. Actinium-228 has a half-life of about 6.15 hours, meaning it takes this amount of time for half of a sample to decay into other elements. This isotope emits beta particles and gamma radiation, making it useful in certain medical applications, such as targeted alpha therapy for cancer treatment. However, due to its radioactivity, handling Actinium-228 requires strict safety precautions to protect against radiation exposure.