Neptunium

Category: actinide Atomic number: 93 Colour: silver Melting point: 637°C (1,179°F) Boiling point: 4,000°C (7,232°F) First identified: 1940

The Italian-American physicist Enrico Fermi tried to create elements 93 and 94 by bombarding thorium and uranium with neutrons. He believed he had succeeded, but it was later shown that he had accidentally discovered nuclear fission and was finding fission products of the original elements. Fermi would go on to work on the Manhattan Project and to build the world’s first nuclear reactor, the Chicago Pile-1.

In 1940, Edwin McMillan and Philip Abelson at Berkeley used Fermi’s method and succeeded in creating element 93, which they named after the planet Neptune, as it is next to Uranus in the solar system. Neptunium is the last naturally occurring element, found in uranium ores in trace amounts. It is also present in vanishingly small quantities in many houses, because the radioactive element americium, which is used in tiny quantities in some smoke detectors, decays to form it.