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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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454 news items

Brainerd Daily Dispatch

Brainerd Daily Dispatch
Sun, 05 Jul 2015 20:33:45 -0700

He wrote about the natural abundance of Minnesota and described in detail the Dakota, including a hunting episode in which they shot buffalo with bow and arrow from a canoes at a river crossing near present day Anoka. It piqued even more interest in ...


Wed, 01 Jul 2015 14:46:58 -0700

Water break on Main Street Car. The water break flooded the street. Courtesy photo by Ross Graf, general manager of Natural Abundance. Water break on Main Street Truck. Workers responded to the water break on Wednesday. American News Photo by ...

Richmond Times-Dispatch

Richmond Times-Dispatch
Thu, 02 Jul 2015 19:37:30 -0700

Other European colonists and settlers followed. The Pilgrims set out for the Chesapeake but landed in what became known as Massachusetts. Yorktown effectively ended the Revolutionary War. The bay offered natural abundance in its waters and ashore.

Huffington Post

Huffington Post
Wed, 01 Jul 2015 09:18:45 -0700

Rouse our pleasure centers, our creativity, and the natural abundance that is inherent there that most of us currently do not have access to because of our disowned emotions and sexuality. We must learn to celebrate our sisters' triumphs, to grieve ...


Thu, 02 Jul 2015 05:30:50 -0700

Paulo's oil paintings are a reflection of what it is to dwell in Florida, a land of natural abundance and color. Titled “Harmony in the Forgotten Garden”, the show will remain as the featured collection through July. (Ocean Art Gallery, 200 S ...


Sun, 28 Jun 2015 17:14:52 -0700

Our agriculture and forestry practices brought phenomenal changes to Nova Scotia's native Acadian forest. Mature forest declined to a fraction of its natural abundance. Old forest species such as red spruce, hemlock and sugar maple shrunk in abundance, ...

Mid Columbia Tri City Herald

Mid Columbia Tri City Herald
Sun, 21 Jun 2015 22:09:17 -0700

Her work in the southern Appalachian mountains, Dolly Parton's proverbial backyard, is the result of the region's natural abundance of diverse lichen. The area, like Hanford and other lichen-rich regions, is a great example of the biodiversity that ...

News & Observer

News & Observer
Mon, 22 Jun 2015 08:35:51 -0700

Though my Soul may set in darkness it will rise in perfect Light; I have loved the Stars too fondly to be fearful of the night. (The Old Astronomer, Sarah Williams). On June 4th our beloved Bonnie ascended on the cusp of the waning Moon. Held and ...

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