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Jai Ganesh

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Neptunium

Neptunium

Gist

Neptunium (Np) is a synthetic, radioactive actinide metal with atomic number 93, discovered in 1940 by Edwin McMillan and Philip H. Abelson. It is the first transuranic element and is produced from uranium in nuclear reactors, with its isotopes, particularly Np-237, found in spent nuclear fuel and used as a target for plutonium-238 production for space missions. The element is highly toxic and poses health risks, primarily cancer, from its radiation if inhaled or ingested, especially from Np-237.

Neptunium is a synthetic radioactive element with very limited, primarily research-focused uses. Its main applications include producing plutonium-238, a heat source for spacecraft and remote devices, and in certain neutron detection instruments. Although it can be a component in nuclear reactors and weapons, its hazardous nature and the availability of other materials make these uses impractical or theoretical. 

Summary

Neptunium is a chemical element; it has symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. It is named after Neptune, the planet beyond Uranus in the Solar System, which uranium is named after. A neptunium atom has 93 protons and 93 electrons, of which seven are valence electrons. Neptunium metal is silvery and tarnishes when exposed to air. The element occurs in three allotropic forms and it normally exhibits five oxidation states, ranging from +3 to +7. Like all actinides, it is radioactive, poisonous, pyrophoric, and capable of accumulating in bones, which makes the handling of neptunium dangerous.

Although many false claims of its discovery were made over the years, the element was first synthesized by Edwin McMillan and Philip H. Abelson at the Berkeley Radiation Laboratory in 1940. Since then, most neptunium has been and still is produced by neutron irradiation of uranium in nuclear reactors. The vast majority is generated as a by-product in conventional nuclear power reactors. While neptunium itself has no commercial uses at present, it is used as a precursor for the formation of plutonium-238, which is in turn used in radioisotope thermal generators to provide electricity for spacecraft. Neptunium has also been used in detectors of high-energy neutrons.

The longest-lived isotope of neptunium, neptunium-237, is a by-product of nuclear reactors and plutonium production. This isotope, and the isotope neptunium-239, are also found in trace amounts in uranium ores due to neutron capture reactions and beta decay.

Details

Neptunium (Np) is a radioactive chemical element of the actinoid series of the periodic table that was the first transuranium element to be artificially produced, atomic number 93. Though traces of neptunium have subsequently been found in nature, where it is not primeval but produced by neutron-induced transmutation reactions in uranium ores, American physicist Edwin M. McMillan and chemist Philip H. Abelson first found neptunium in 1940 after uranium had been bombarded by neutrons from the cyclotron at Berkeley, California. The element was named after the planet Neptune, which is the first planet beyond Uranus.

Neptunium has been produced in weighable amounts in nuclear reactors. In breeder reactors it is a by-product of plutonium production from uranium-238 (about one part neptunium is produced for every 1,000 parts plutonium). All neptunium isotopes are radioactive; the stablest 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 more than 2 microseconds. Neptunium-237 can be separated from used reactor fuel to study the physical and chemical properties of the element.

Neptunium, a silvery metal, exists in three crystalline modifications; the room-temperature form (alpha) is orthorhombic. Neptunium is chemically reactive and is more similar to plutonium than to uranium, with oxidation states from +3 to +7. Neptunium ions in aqueous solution possess characteristic colours: Np3+, pale purple; Np4+, pale yellow-green; NpO2+, green-blue; varying from colourless to pink or yellow-green, depending on the anion present; and Np7+, dark green. Compounds of neptunium have been prepared in all oxidation states +3 to +7; they are generally similar to compounds of uranium and plutonium with the same oxidation state.

Element Properties

atomic number  :  93
stablest isotope  :  237
melting point  :  640 °C (1,184 °F)
specific gravity (alpha)  :  20.45
oxidation states  :  +3, +4, +5, +6, +7.

Additional Information:

Appearance

A radioactive metal.

Uses

Neptunium is little used outside research. The isotope neptunium-237 has been used in neutron detectors.

Biological role

Neptunium has no known biological role. It is toxic due to its radioactivity.

Natural abundance

Neptunium is obtained as a by-product from nuclear reactors. It is extracted from the spent uranium fuel rods. Trace quantities occur naturally in uranium ores.

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