Neptunium

The neptunium is a chemical element of synthesis of symbol Np and Atomic number 93.

metal Element Radioactive, neptunium is the first of the transuranians and belongs to the series of the Actinide S . Its most stable isotope, neptunium-237, is produced in the nuclear reactors. One also finds it in the form of traces in the ore of Uranium.

Il was discovered at the University of California. As it comes after uranium in the periodic table, it was baptized in reference to the planet Neptune, which comes after Uranus in the Solar system.

Characteristics

Of silver plated appearance, this metal is chemically rather reactive, and one finds it at least under three structures:
  • alpha-neptunium, Orthorhombic, density 20.250 kg/m ³,
  • beta-neptunium (above 280°C), tétragonal, density (with 313°C) 19.360 kg/m ³, and
  • gamma-neptunium (above 577°C), cubic, density (with 600°C) 18.000 kg/m ³.

This element has four states of ionic oxidation:

  • Np: n.o. = +III (pale crimson), similar to the rare ion Pm,
  • Np: n.o. = +IV (yellow-green);
  • : n.o. = +V (blue-green);
  • : n.o. = +VI (pink pale).

History

Neptunium was discovered by Edwin McMillan and Philip Abelson in 1940. The discovery was made in the Berkeley Radiation Laboratory of the University of California, in Berkeley, where the team produced the isotope Np of neptunium (2,4 days of half-life) by bombarding Uranium with Neutron S accelerated.

Isotopes

Nineteen radio Isotope S of neptunium were defined. Most stable is Np with a half-life of 2,14 million years, while Np has a 154.000 years half-life, and the 396,1 day old Np. The half-life of all the other isotopes is lower than 4,5 days, and in the majority of the cases lower than 50 minutes. The atomic weight of the isotopes of neptunium goes from 225,0339 U (Np) to 244,068 U (Np).

Military applications

In September 2002, of the researchers of the University of California working for a project of American weapons of massive destruction, created the first nuclear critical mass founded on the use of the neptunium-237 rather than of the Plutonium or the Uranium.

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