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2009-07-09 17:04:18

Actinium is a radioactive chemical element. The symbol for Actinium is Ac and the atomic number is 89. Actinium was discovered in 1899 by French chemist André-Louis Debierne. It was the first non-primordial radioactive element to be isolated. Actinium is amongst a group of 15 similar elements within the periodic table that make up the actinoid series. This substance was also independently discovered by Friedrich Oskar Giesel in 1902 and named it emanium in 1904. In 1904 he named it...

2005-05-26 08:39:06

In geology, the mineral monazite is a reddish-brown phosphate containing rare earth metals and an important source of thorium, lanthanum, and cerium. It occurs usually in small isolated crystals. There are actually three different kinds of monazite, depending on relative elemental composition of the mineral: - monazite-Ce (Ce, La, Nd, Th, Y)PO4 - monazite-La (La, Ce, Nd)PO4 - monazite-Nd (Nd, La, Ce)PO4 The elements in parentheses are listed in the order in which they are in relative...

2005-05-25 18:46:47

A rare earth is an oxide of a rare earth element. Often rare earth elements themselves are loosely called "rare earths". As to exactly what is a "rare earth" element is a matter of some ambiguity. The narrowest definition restricts it to the lanthanides, which are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Sometimes the radioactive actinides are included, so that all elements...

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Word of the Day
  • A pivoted catch designed to fall into a notch on a ratchet wheel so as to allow movement in only one direction (e.g. on a windlass or in a clock mechanism), or alternatively to move the wheel in one direction.
The word 'pawl' probably comes from a Latin word meaning 'stake'.