Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic tableand the first of the actinide series of metallic elements that share similar chemical and physicalcharacteristics. Actinium is also closely related in its characteristics to the element lanthanum,which is located just above it in group 3. The elements in this series range from atomic number89 (actinium) through 103 (lawrencium). Actinium’s most stable isotope is actinium-227,with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 throughbeta decay, and both of these isotopes are decay products from uranium-235.
