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Relative abundance of elements.png

In chemistry, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from planet to planet, and even from place to place on the Earth, but remains relatively constant in time (on a short-term scale).

As an example, uranium has three naturally occurring isotopes: 238U, 235U and 234U. Their respective natural mole-fraction abundances are 99.2739–99.2752%, 0.7198–0.7202%, and 0.0050–0.0059%.[1] For example, if 100,000 uranium atoms were analyzed, one would expect to find approximately 99,274 238U atoms, approximately 720 235U atoms, and very few (most likely 5 or 6) 234U atoms. This is because 238U is much more stable than 235U or 234U, as the half-life of each isotope reveals: 4.468×109 years for 238U compared to 7.038×108 years for 235U and 245,500 years for 234U.

Exactly because the different uranium isotopes have different half-lives, when the Earth was younger, the isotopic composition of uranium was different. As an example, 1.7 billion years ago the NA of 235U was 3.1% compared to today's 0.7%, and for that reason a natural nuclear fission reactor was able to form, something that cannot happen today.

However, the natural abundance of a given isotope is also affected by the probability of its creation in nucleosynthesis (as in the case of samarium; radioactive 147Sm and 148Sm are much more abundant than stable 144Sm) and by production of a given isotope by natural radioactive isotopes (as in the case of radiogenic isotopes of lead).

Deviations from natural abundance[edit]

It is now known from study of the sun and primitive meteorites that the solar system was initially almost homogeneous in isotopic composition. Deviations from the (evolving) galactic average, locally-sampled around the time that the sun's nuclear burning began, can generally be accounted for by mass fractionation (see the article on mass-independent fractionation) plus a limited number of nuclear decay and transmutation processes.[2] There is also evidence for injection of short-lived (now extinct) isotopes from a nearby supernova explosion that may have triggered solar nebula collapse.[3] Hence deviations from natural abundance on earth are often measured in parts per thousand (per mil or ‰‰) because they are less than one percent (%). The single exception to this lies with the presolar grains found in primitive meteorites. These bypassed the homogenization, and often carry the nuclear signature of specific nucleosynthesis processes in which their elements were made.[4] In these materials, deviations from "natural abundance" are sometimes measured in factors of 100.

See also[edit]

Footnotes and References[edit]

  1. ^ Uranium Isotopes, retrieved 14 March 2012 
  2. ^ Robert N. Clayton (1978) Isotopic anomalies in the early solar system, Annual Review of Nuclear and Particle Science 28:501–522.
  3. ^ Ernst Zinner (2003) An isotopic view of the early solar system, Science 300:5617, 265–267.
  4. ^ Ernst Zinner (1998) Stellar nucleosynthesis and the isotopic composition of presolar grains from primitive meteorites, Annual Review of Earth and Planetary Sciences 26:147–188.

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Natural_abundance — Please support Wikipedia.
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447 news items

Deseret News

Deseret News
Thu, 18 Dec 2014 22:51:11 -0800

Particularly for Americans, living as we do in a young country blessed with astonishing natural abundance, wastefulness has often seemed worth the bargain. In earlier generations it was often said, and not only by the French, that a French housewife ...
 
Nature.com
Wed, 17 Dec 2014 10:11:17 -0800

Researchers have therefore begun to explore cheaper alternatives to palladium for these reactions. Iron, with its high natural abundance and low cost, is a logical choice. Many iron-catalysed C–C bond-forming reactions have been discovered in the past ...
 
New Zealand Herald
Wed, 17 Dec 2014 13:00:00 -0800

The writer with a homemade, green-living aesthetic lives in an 80sq m house with her partner and 7-year-old son. She's heading to Wellington and Wanganui for extended Christmases with two sides of her family. Living by the beach on Auckland's West ...

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Wed, 17 Dec 2014 16:22:30 -0800

Deuterium has a natural abundance of about 1%, and is present in about one in every 50 water molecules on Earth. It has the same size and shape as a hydrogen atom, and differs only in forming very slightly stronger chemical bonds. The removal of a ...

San Antonio Magazine

San Antonio Magazine
Wed, 17 Dec 2014 08:30:00 -0800

Access to much of this natural abundance is made possible by the miles of canals that connect the different hotels at Mayakoba. Travel by boat may be romantic and relaxing for any visitor, but it becomes a constant learning opportunity when you're with ...

Christian Post (blog)

Christian Post (blog)
Mon, 15 Dec 2014 13:56:15 -0800

The other is natural abundance. By weighing the consequences of the disorder, we also can become more aware of how blessed our children can be—biologically, cognitively, and spiritually—through positive physical connection to nature.” Nature is good ...
 
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Tue, 16 Dec 2014 09:03:45 -0800

THERE are just some Palaro events that perennial regional meet champion Cagayan de Oro can hardly dominate despite its natural abundance of talents. And one can always consider chess and volleyball among the few of them. Both competitions now ...

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Thu, 11 Dec 2014 23:04:36 -0800

The Natural Abundance heath food store has a new general manager and a new idea will likely get some cheers from home brewers in the area. General manager Ross Graf, who took over for Lara Nelson in October, said he's planning to carry home brew ...
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