Britannica Nobel Prize: Radium: Detailed overview and data.
ChemGlobe: Radium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Radium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Radium: Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Radium: Basic physical and historical information.
LANL: Radium: History, sources, properties, and uses.
Lenntech: Radium: Physical data, chemical properties, health and environmental effects.
Radiochemistry of Radium: Full text of the monograph by Murrell L. Salutsky (W.R. Grace & Co., Research Division, Washington Research Center, Clarksville, Maryland) and H. W. Kirby (Mound Laboratory, Miamisburg, Ohio). [PDF]
Radium: Data tables and historic information.
Visual Elements: Radium: Image, general and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Radium: Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Radium: Properties of the element, including its history, applications, and charateristics.