Ac-227, or Actinium-227, is a radioactive isotope of the element Actinium. It is part of the uranium decay series and is produced from the decay of thorium-231. Ac-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, Ac-227 must be handled with care in controlled environments to ensure safety and minimize exposure to radiation.