QUICK REFERENCE
- Symbol: Np
- Atomic Number: 93
- Atomic Weight: [237]
- Element Classification: Actinide
- Discovered By: Edwin McMillan and Philip H. Abelson
- Discovery Date: 1940
- Name Origin: Named after the planet Neptune, following the pattern of uranium (named after Uranus) and plutonium (named later, after Pluto)
- Density(g/cc): 20.45
- Melting Point: 644°C
- Boiling Point: 4000°C (estimated)
- Appearance: Silvery metallic
- Atomic Radius(pm): 175 (estimated)
Discovery
Neptunium was discovered in 1940 by American physicists Edwin McMillan and Philip H. Abelson at the Berkeley Radiation Laboratory (now Lawrence Berkeley National Laboratory). They produced neptunium by bombarding uranium-238 with slow neutrons to create uranium-239, which then underwent beta decay to form neptunium-239. This discovery marked the first identification of a transuranium element, extending the periodic table beyond uranium.
Relation to Other Elements
Neptunium is the first element in the actinide series that is synthetic and does not occur in significant amounts in nature. It shares characteristics with other actinides, such as being radioactive and having multiple oxidation states, with +3, +4, +5, and +6 states occurring in solutions. Neptunium-237, its most stable isotope, has a half-life of about 2.14 million years and can be found in trace amounts in uranium ores as a result of neutron capture and beta decay processes.
Natural Occurrence
While neptunium is primarily a synthetic element, trace amounts of neptunium-237 can be found in the environment as a result of the decay of uranium and the interaction of uranium ores with neutrons produced by the spontaneous fission of uranium or by cosmic rays.
Uses
Neptunium’s uses are limited and primarily related to research and specific nuclear applications:
- Nuclear Science: Neptunium-237 is used in research and for the production of plutonium-238, which is used in radioisotope thermoelectric generators (RTGs) for powering spacecraft.
- Potential Nuclear Fuel: Neptunium has been considered as a component in mixed oxide (MOX) fuel for nuclear reactors, given its capacity to undergo fission and contribute to the reactor’s energy output.
The discovery of neptunium not only expanded the periodic table but also advanced the understanding of nuclear chemistry and the synthesis of new elements. Its identification opened the door to the discovery of further transuranium elements, contributing significantly to the development of nuclear science and technology.