Actinium isotopes are variants of the chemical element actinium, which has the atomic number 89. The most common isotope, actinium-227, is radioactive and has a half-life of about 21.8 years. It is primarily produced from the decay of thorium-232 and is used in various applications, including targeted alpha-particle therapy for cancer treatment. Other isotopes of actinium, such as actinium-228 and actinium-226, also exist but are less prevalent. These isotopes are important in scientific research and can be used in nuclear medicine. Due to their radioactivity, handling actinium isotopes requires strict safety protocols.