See also:

• Science: Chemistry: Elements: Actinides  (2)

• Britannica Nobel Prize: Neptunium - Overview and basic data.
• ChemGlobe: Neptunium - Electronic, thermal, and steric data along with an isotope table.
• ChemicalElements.com: Neptunium - Basic information, atomic structure, and isotopes table.
• EnvironmentalChemistry.com: Neptunium - Atomic structure, chemical and physical properties, and table of nuclides.
• It's Elemental: Neptunium - Basic physical and historical information.
• LANL: Neptunium - Basic information and history.
• Lenntech: Neptunium - Physical data, chemical properties, health and environmental effects.
• Visual Elements: Neptunium - General and physical information, source, and key isotopes.
• WebElements: Neptunium - Extensive information on history, uses, compounds, and properties.
• Wikipedia: Neptunium - Notable characteristics, history, occurrence, isotopes, and weapons applications.