Neptunium

Neptunium was the first transuranic element: the first element beyond uranium, to be created artificially. Made at Berkeley in 1940 by bombarding uranium with neutrons, it appeared in nature only in tiny traces as a product of neutron capture in uranium ores. Named after the planet Neptune.

• Atomic Number9393 protons, 93 electrons
• Atomic Mass237.048172 u93× heavier than hydrogen
• State at Room TempSolidSolid
• Density20.25 g/cm³
• Melting / Boiling643.9°C / 3901.8°C
• Discovered1940

What is Neptunium?

Neptunium has 93 protons and the most stable isotope, neptunium-237, has a half-life of 2.14 million years. Np-237 is produced in nuclear reactors and is found in spent nuclear fuel. Discovered in 1940 by Edwin McMillan and Philip Abelson at Berkeley.

Fact Neptunium is element 93, symbol Np. As an actinide, it is part of the f-block of the periodic table: one of 15 radioactive elements from actinium (89) to lawrencium (103). All actinides are radioactive; none has a stable isotope. They are produced in nuclear reactors and by decay of heavier elements, and their chemistry has been studied using only microgram or nanogram quantities.

Where you find Neptunium

On Earth

Neptunium does not occur in significant natural abundance. It is found in trace quantities in uranium ores as a product of neutron capture and radioactive decay. World production is measured in micrograms or milligrams per year.

How we use Neptunium

Neptunium has 93 protons and the most stable isotope, neptunium-237, has a half-life of 2

How it was discovered

Neptunium has 93 protons and the most stable isotope, neptunium-237, has a half-life of 2.14 million years. Np-237 is produced in nuclear reactors and is found in spent nuclear fuel. Discovered in 1940 by Edwin McMillan and Philip Abelson at Berkeley.

Deeper dive: neptunium and the actinide series

The actinides (elements 89-103) form the lower of the two rows below the main body of the periodic table. They represent the filling of the 5f electron subshell. Unlike the lanthanides (the upper row), the actinides show greater variety in their chemistry because the 5f, 6d and 7s orbitals are close in energy. The early actinides, thorium through neptunium, can show many different oxidation states (e.g. uranium from +3 to +6). The heavier actinides increasingly resemble the lanthanides in preferring the +3 state.

All actinides beyond bismuth (83) are radioactive. The lightest, thorium, protactinium and uranium, have long enough half-lives to survive from the formation of the solar system. Neptunium and beyond are almost entirely synthetic, produced in nuclear reactors or accelerators. The transuranic elements were created at remarkable facilities including Oak Ridge National Laboratory, the Berkeley Cyclotron, the GSI in Darmstadt and JINR in Dubna.

Moving to 94 protons brings us to the next element on the periodic table.