Neptunium

Early in 1934, Enrico Fermi began an experiment that bombarded uranium with neutrons. He was trying to produce elements 93 and 94. His team was initially reluctant to publicize the claim that they might have found element 93, but they did publish a paper entitled "Possible Production of Elements of Atomic Number Higher than 92" in June 1934. Many theoretical objections were quickly raised. Several other experiments attempted to create element 93, but they all failed.

In 1939, physicist Edwin McMillan began an experiment bombarding uranium with neutrons in the 60-inch cyclotron at the University of California, Berkeley. He found a fission product whose half-life of 2.3 days was unknown. He took the sample to Emilio Segrè to isolate the source of the radioactivity. The two scientists believed that the unknown half-life was simply another fission product of uranium.

However, early in 1940, McMillan and Philip Abelson, another chemist, tried again to find out what was causing the unknown half-life. Abelson noticed that whatever was producing this half-life did not have a chemistry like any other known element but that it was similar to uranium. After bombarding another sample, they proved that a new element had been discovered.

Neptunium is one of three elements that are named for planets (or Roman gods, if you prefer). Because uranium was named for Uranus, neptunium was named for Neptune, the next planet beyond Uranus.

Neptunium, like most actinides, is a ductile, silvery, radioactive metal that tarnishes when exposed to air. It has a low melting point. Its boiling point is not empirically known but is guessed at from its vapor pressure. It has the largest liquid range of any element. It is the densest element of all the actinides and the fifth most dense of all naturally occurring elements. It can exhibit magnetic behavior.

Neptunium is used in neutron detectors and basic scientific research. It is also used to produce plutonium.

Neptunium forms a variety of compounds such as halides, hydrides, fluorides, chlorides, bromides, sulfides, nitrides, and oxides (where known).

Neptunium exists in three crystalline forms: orthorhombic, tetragonal, and body-centered cubic. It is a man-made metal.

There are 24 characterized isotopes of neptunium, and all are radioactive; the most stable is neptunium-237 with a half-life of 2,144,000 years, and among the most unstable is neptunium-225 with a half-life of little more than 2 microseconds.

Neptunium is present in nature in extremely small amounts. Trace amounts of neptunium are found as decay products in uranium ores. Most neptunium that is found in the environment came from atmospheric nuclear explosions.

Neptunium is obtained as a by-product from nuclear reactors, extracted from the spent uranium fuel rods.