Neptunium

-
.
Neptunium, symbol Np, radioactive metallic element with an atomic number of 93. Neptunium is one of the transuranium elements in the actinide series of the periodic table. Neptunium is a silvery metal that exists in at least three different crystalline forms, hence the variations in specific gravity (from 18 to 20). The element is reactive and shows four ionic oxidation states. It was discovered in 1940 by the American physicists Edwin M. McMillan and Philip H. Abelson. It is produced by bombardment of uranium-238 with neutrons; the resultant uranium-239 decays radioactively by emitting a beta particle to form neptunium-239. The neptunium isotope in turn emits a beta particle, forming the important isotope plutonium-239, one of the materials of which atomic bombs are made.

Isotopes of neptunium with mass numbers from 228 to 242 are known. The most stable, neptunium-237, has a half-life of 2.14 million years. It was discovered by the American chemists Glenn T. Seaborg and Arthur C. Wahl. This long-lived isotope served as a useful research tool in the atomic bomb project and is used in studies of chemical reactivity. Neptunium occurs in nature in trace amounts in uranium ores but is produced artificially. It is used as a component in neutron detection devices. See also Radioactivity.

Neptunium melts at about 630° C (about 1166° F), and boils at about 5235° C (about 9455° F). The atomic weight of neptunium is 237.0482.

Comments

Post a Comment

Popular posts from this blog

Beryllium

-
. Beryllium, symbol Be, gray, brittle metallic element, with an atomic number of 4. It is in group 2 (or IIa) of the periodic table (see Periodic Law ). Beryllium was named for its chief mineral, beryl , an aluminum beryllium silicate. It was discovered as an oxide, now known as beryllia, in 1797 by French chemist Louis Nicolas Vauquelin. The free element was first isolated in 1828 independently by Friedrich Wöhler and Antonine Alexandre Brutus Bussy. Because the soluble compounds are sweet-tasting, the new element was first called glucinium, a reference to the sugar glucose . PROPERTIES AND OCCURRENCE Beryllium, one of the alkaline earth metals , ranks about 51st in natural abundance among the elements in the earth's crust. Its atomic weight is 9.012. Beryllium melts at about 1287° C (about 2349° F), boils at about 3000° C (about 5432° F), and has a specific gravity of 1.85. Beryllium has a high strength per unit weight. It tarnishes only slightly in air, becoming covered with a
Read more

Electricity and Magnetism

-
Image
. Many similarities exist between electric and magnetic phenomena. A magnet has two opposite poles, referred to as north and south. Opposite magnetic poles attract each other, and similar magnetic poles repel each other, exactly as happens with electric charges. The force with which magnetic poles attract or repel each other depends on the strength of the poles and the distance between them. This relationship is similar to the Coulomb’s inverse square law for electric charges. See also Magnetism . The similarities between electric and magnetic phenomena indicate that electricity and magnetism are related. Electricity produces magnetic effects and magnetism produces electric effects. The relationship between electricity and magnetism is called electromagnetism. See also Quantum Electrodynamics . Magnetic Effects of Electricity It has been noted that an electric field exists around any electric charge. If electric charges are moving, they constitute an electric current. The magnetic eff
Read more

Electric Fields

-
Image
A single electric charge can attract or repel, and it will demonstrate this ability as soon as another charge is brought near it. The ability to attract or repel can be thought of as being stored in the region around the charge. This region is called the electric field of force of the charge. All charged objects have electric fields around them. Lines of Force An electric field can be visualized as consisting of imaginary lines called lines of force. Each line corresponds to the path that a positive charge would take if placed in the field on that line. The lines in the field around a positively charged object radiate in all directions away from the object, since the object repels positive charges. Conversely, the lines in the field around a negatively charged object are directed toward the object. If a positive and a negative object are placed near each other, their lines of force connect. If two objects with similar charges are placed near each other, the lines do not connect. Li
Read more