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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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24 news items

Wed, 29 Oct 2014 11:00:00 -0700

They were also impassioned and vital for a place that, despite being blessed with so much natural abundance and human talent, should and does strive to be better. It is our fervent hope that such conversations continue well after this week. Indeed ...
Pensions & Investments
Tue, 28 Oct 2014 14:56:15 -0700

... well-developed markets, but do so with an investment strategy that has the potential to systematically harness the market's natural abundance of volatility to generate smaller, but safer, returns via regular rebalancing of large numbers of stocks ...
Santa Monica Daily Press
Sun, 26 Oct 2014 11:45:00 -0700

Instead of restricting water usage in our sodden city, perhaps City Hall should consider sharing our natural abundance with the less fortunate residents elsewhere in California? We are a generous city, deeply concerned about the environment. Surely we ...
Olive Press
Thu, 30 Oct 2014 02:46:04 -0700

FOR a true taste of the natural abundance on this region's doorstep, you'll walk miles to find a tastier meal than the last supper we enjoyed at the Botanic Bar in Capileira. The menu is a cornucopia of local produce, making it the perfect finale to ...
Sat, 18 Oct 2014 00:12:52 -0700

I know that customers of Natural Abundance call it Nat Abu for short. I know that Bruce Kleinsasser runs cheer and dance in this town. How long have I been around? I remember when Steve Kehm and Dan Cleberg had pony tails. I refer to Tiospa Zina as ...
NBC Bay Area
Tue, 21 Oct 2014 12:07:30 -0700

For them, it was associated with natural abundance like it was for Indians, but then it had connotations of being a symbol of wild nature and cultural backwater. So people ate it when they had to but then they preferred to eat European food, like ...
Tue, 21 Oct 2014 21:41:15 -0700

We enjoy a natural abundance of cropland to grow food that can be sold locally or exported around the world. We need to develop other crops like grapes for the budding wine industry in our county and we need to invest more in the maple syrup and apple ...
Moultrie News
Thu, 02 Oct 2014 07:26:15 -0700

Of all the wonderful natural abundance we have here on our coast, the wax myrtle is right up at the top in my estimation. Next time you smell the alluring scent of a bayberry candle, give the valiant wax myrtle an appreciative nod. It has been doing ...

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