We continue to review important materials in heat treatment and metallurgy.  

Neptunium (chemical symbol: Np)

Neptunium (Fig. 1) is a silvery, radioactive metal that is ductile and will oxidize in air. Handling of neptunium is very dangerous due to the combination of it being poisonous and pyrophoric. It is also retained in human bones after long exposure. It was the first trans-uranium element (i.e., the elements after uranium) to be produced.

On the periodic table, neptunium is between the elements of uranium and plutonium. All three elements have a large enough nucleus to undergo a nuclear fission reaction (Fig. 2), wherein larger nuclei split into smaller, lighter ones. Since neptunium was discovered much later than both uranium and plutonium, it is not as widely used.

Neptunium was first successfully produced by Edwin McMillan and Philip Abelson at the University of California in 1940 while bombarding uranium-238 with neutrons. The duo were able to prove chemically that a new element was produced, neptunium-239, which had a half-life of just 2.3 days.

Two years later, the longer-living isotope, neptunium-237, with a half-life of 2.14 million years, was discovered by A.C. Wahl and Glenn Seaborg while using a similar technique. McMillan and Abelson named the new element after the planet Neptune, which exists between the planets of Uranus and Pluto, since the theme started by Martin Klaproth was naming uranium after the planet Uranus and, subsequently, plutonium being named after the planet Pluto.

Applications of neptunium are extremely limited, but it does see some use for research purposes, particularly for its consideration as a fissile nuclear fuel. It is currently not being utilized for this type of application. Neptunium-237 can be bombarded with neutrons to create plutonium-238, which is then used to create nuclear batteries to power satellites (Fig. 3) and spacecraft for very long durations of time. Another use of neptunium is in high-energy neutron detection equipment for scientific purposes.

Here are a few important facts about Neptunium.[2,5]

  • Atomic number: 93
  • Atomic weight: 237
  • Melting point: 917 K (644°C or 1191°F)
  • Boiling point: 4175 K (3902°C or 7056°F)
  • Density: 20.25 grams per cubic centimeter
  • Phase at room temperature: Solid
  • Element classification: Metal
  • Period number: 7    
  • Group number: none    
  • Group name: Actinide
  • Electron configuration: [Rn] 5f4 6d17s2



  1. KnowledgeDoor (www.knowledgedoor.com)
  2. Chemicool (www.chemicool.com/)
  3. Wikipedia (www.wikipedia.org)
  4. Royal Society of Chemistry (rsc.org)
  5. Los Alamos National Lab (https://www.lanl.gov/)
  6. The Atomic Archive (http://www.atomicarchive.com/Fission/Fission1.shtml)