Ac=ACTINIUM
Actinium starts the series of actinoids (elements 90-103), which are named after this element. It naturally occurs from uranium decay, the half-life of its most stable isotope 227 is less than 22 years. It has very few applications, because it is difficult to handle and very dangerous. Chemically, it is similar to lanthanum. Most actinium decays to thorium, about 1.4% to francium.
