Actinium-227 is a radioactive isotope of the element Actinium, which has the atomic number 227. It is part of the uranium decay series and is produced from the decay of thorium-231. Actinium-227 has a half-life of about 21.8 years, meaning it takes that long for half of a sample to decay into other elements. This isotope emits alpha particles and is used in various applications, including targeted alpha therapy for cancer treatment. Due to its radioactivity, handling Actinium-227 requires strict safety precautions to protect against radiation exposure.