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Relative abundance of elements.png

In physics, 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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795 news items

Rockford Register Star

Rockford Register Star
Fri, 05 Feb 2016 14:29:34 -0800

Despite this natural abundance, less than half of the minerals consumed by America's manufacturers are actually sourced domestically. And the problem, when it comes to extracting new minerals, is mostly a bureaucratic one. It now takes as much as seven ...

WWNO

WWNO
Wed, 03 Feb 2016 11:30:00 -0800

“The natural abundance of what we've had since the beginning has been just pronounced each and every day and we're blessed to have that natural growth, but for the future we're going to have to look at some other ideas," Sunseri says. "Aquafarming ...

Chillicothe Gazette

Chillicothe Gazette
Mon, 01 Feb 2016 13:22:30 -0800

Despite this natural abundance, less than half of the minerals consumed by America's manufacturers are actually sourced domestically. And the problem, when it comes to extracting new minerals, is mostly a bureaucratic one. It now takes as much as seven ...

Huffington Post Canada

Huffington Post Canada
Thu, 28 Jan 2016 14:48:26 -0800

Oil, gas and the resource sector more broadly are a very important part of our economy, representing 10 per cent of our Gross Domestic Product (GDP). Canada has been blessed with a natural abundance of natural resources from forestry and minerals, to ...

ITV News

ITV News
Tue, 26 Jan 2016 07:22:30 -0800

Britain is home to a huge variety of landscapes, and their sheer natural abundance takes centre stage as Griff investigates how they have each dictated different ways of living, working and playing – both in the past and as they are now - across the ...

The Hindu

The Hindu
Thu, 28 Jan 2016 16:08:38 -0800

“Growing up, Kerala was this mythical place of elephants, temples, rice fields and great natural abundance,” says Mr. Nair, who is in the city with a global leaders programme organised by the Global Institute For Tomorrow (GIFT), an independent pan ...
 
Newswise (press release)
Thu, 21 Jan 2016 21:00:42 -0800

For example, in a paper in the Journal of the American Chemical Society, Ames Laboratory scientist Marek Pruski and his research team reported on DNP studies of natural abundance oxygen (17O) in several materials. Oxygen is practically undetectable by ...

Scientist Live

Scientist Live
Sun, 31 Jan 2016 22:33:45 -0800

31P is a 100% natural abundance nucleus commonly found in many organic compounds. The high NMR sensitivity of 31P combined with its large chemical shift range, simple spectra, and absence of impurities in the background spectrum make 31P NMR ...
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