Neptunium longest lived isotope

The longest lived isotope is neptunium-237. Its half life is 2,144,000 years. The half life of a radioactive element is the time it takes for half of a sample of the element to break down. Of a sample of neptunium-237,... 

But neptunium is a different story. Its longest lived isotope is neptunium-237, with a half life of about two million years. If 100 million tonnes of neptunium were present at Earth s beginning, only 50 million tons would be left after two million years. After another two million years (four million years altogether), only 25 million tons would be left. After another two million years (six million years altogether), only 12.5 million tons would be left. 

Synthesis of neptunium exhibited a significant feature which was to prove typical for syntheses of all transuranium elements (and other synthesized elements, too). First, one isotope with a certain mass number was synthesized. For neptunium this was neptunium-239. From that time it became a rule to date a discovery of a new transuranium element by the time of reliable synthesis of its first isotope. But sometimes this isotope proved to be so short-lived that it was difficult to subject it to physical and chemical analyses let alone find a useful application for it. A study of a new element would best be conducted with its longest-lived isotope. In the case of neptunium this was iieptunium-237 synthesized in 1942 in the following reaction ... 

The longest-lived isotope of americium is Am with a half-life of about 7370 years. Other relatively long-lived isotopes are Am and Am. Americium can also form four oxidation states in aqueous solution trivalent, tetravalent, pentavalent and hexavalent. No data are available for the tetravalent and hex-avalent oxidation states and only a relatively small amount for both the trivalent and pentavalent states. The behaviour of all oxidation states should be reasonably similar to those of uranium, neptunium and plutonium. 

Neptunium, the first transuranium element, was discovered hy E. M. McMdlan and P. H. Ahelson in 1940 in Berkeley, California. It was produced in the cyclotron in a nuclear reaction by bombarding uranium-238 with neutrons. An isotope of mass 239 and atomic number 93 and ti/2 of 2.4 days was produced in this reaction. Neptunium-237, the longest-lived alpha-emitter with half-life 2.14x10 years, was discovered two years later in 1942 by Wahl and Seaborg. The new element was named after the planet Neptune, the planet next to Uranus in the solar system. 

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