Actinium: Data tables and historic information.
ChemGlobe: Actinium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Actinium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Actinium: Atomic structure, properties, and table of nuclides.
It's Elemental: Actinium: Basic physical and historical information.
LANL: Actinum: Basic information and history.
Lenntech: Actinium: Physical data, chemical properties, health and environmental effects.
Visual Elements: Actinium: Image, sources, biological role, key isotopes, and oxidation states.
WebElements: Actinium: Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Actinium: Details the properties of the element, including its history, applications, and characteristics.
