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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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31 news items

 
MLive.com
Sun, 03 Aug 2014 02:56:15 -0700

084 med.jpg A bench along the shores of Lake Huron provides a nice place to relax and listen to the waves. Howard Meyerson. It was mid-afternoon when I kicked off my boots and sat down on a bench at the edge of a cobblestone beach along Lake Huron.
 
Three Lions Roar
Wed, 27 Aug 2014 11:11:15 -0700

England, on the other hand, has a natural abundance of fullbacks on both sides. Not only that, but many of these players are among the best in the world. To boot, England has a number of young fullbacks that will have the opportunity to prove ...
 
Burnaby NewsLeader
Wed, 27 Aug 2014 19:37:30 -0700

... all those kinds of things. "These are the reasons British Columbians choose to live here and work here and it's the reason people choose to visit, is that beauty and that natural abundance that we have here, that would really be at risk by an oil ...
 
Deutsche Welle
Tue, 26 Aug 2014 06:30:00 -0700

It's little wonder then that traveling to the region in 1799, Prussian explorer and naturalist Alexander von Humboldt was so overwhelmed by the natural abundance he encountered that he wrote, “I will take leave of my senses if these wonders do not soon ...

Vancouver Sun

Vancouver Sun
Mon, 25 Aug 2014 06:41:15 -0700

... the Nature Conservancy, the Pacific Salmon Foundation, the Tyee Club and volunteers from small local environmental groups and fish and game associations, they've been realizing incremental recovery of the natural abundance degraded by progress.
 
AberdeenNews.com
Thu, 14 Aug 2014 15:08:45 -0700

The familiar Natural Abundance radish is still the centerpiece. To check it out, visit the food co-op's Facebook page. • As with any planned building project or new business intention, nothing is ever certain until the doors actually open, but the plot ...
 
AberdeenNews.com
Wed, 06 Aug 2014 13:17:48 -0700

Locally, the tea can be found at a number of retailers, including Kessler's, Ken's SuperFair Foods and Natural Abundance, but individual customers can also place direct orders online, which is what a customer in the Netherlands did when purchasing 320 ...
 
The Australian
Mon, 11 Aug 2014 07:11:36 -0700

The people of the sparsely vegetated western region of Kutch lack the natural abundance of foods in the lush, fecund southern states; nonetheless they have a characteristic food style. Hearty flatbread made from ground millet drizzled with fresh butter ...
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