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Relative abundance of elements.png

In chemistry, natural abundance (NA) refers to the abundance[clarification needed] of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average) 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.

As an example, uranium has three naturally occurring isotopes: 238U, 235U and 234U. Their respective NA range from 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 99,275 238U atoms, 720 235U atoms, and no more than 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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Comox Vallety Record
Wed, 16 Apr 2014 14:56:15 -0700

The abundance of product from wine to oysters and everything in between in the Comox Valley is evident to locals, but is also growing in popularity for those elsewhere. The growth, particularly targeting those outside the Valley, is creating a growing ...
 
HSUS News
Mon, 21 Apr 2014 09:52:30 -0700

A natural abundance of seeds, berries, and caterpillars will do more for backyard birds than any buffet you can provide them—and will keep the unexpected dangers of artificial materials at bay. Share photos of your humane backyard on Facebook, Twitter ...
 
Azom.com
Tue, 15 Apr 2014 01:26:15 -0700

... including automotive catalytic converters and industrial catalysts (e.g. from the chemical and petrochemical industries) contain Precious Metals and specifically the Platinum Group Metals (PGMs) that are valuable as a result of their low natural ...
 
Huffington Post Canada
Tue, 15 Apr 2014 09:54:05 -0700

Around the world, we have built most of our cities in places of high biodiversity and places of natural abundance, such as coastal areas, river valleys and habitat edges. In cities like Toronto, while we have almost obliterated the original landscape ...

Azom.com

Azom.com
Mon, 14 Apr 2014 03:30:00 -0700

Precious Metals and specifically the Platinum Group Metals (PGM's) are valuable because of their low natural abundance, their unique properties and the complex processes that are required for their extraction and refining from primary sources. While ...

Twain Harte News

Twain Harte News
Fri, 11 Apr 2014 13:58:29 -0700

... connection with people you might normally tend to pass by and take for granted. 3. Use a skill or talent you have – cooking, accounting, decorating – to help someone who could benefit from it. It will reconnect you to the natural abundance in your ...
 
nanotechweb.org
Thu, 17 Apr 2014 04:48:45 -0700

With its high theoretical capacity, natural abundance, low cost and environmental benignity, Fe3O4 is an appealing alternative anode material for lithium-ion batteries. However, similar to other transition metal oxides (MxOy), it has an extremely low ...

Boston Globe

Boston Globe
Sat, 29 Mar 2014 22:00:24 -0700

A place of natural abundance in the heart of the crowded suburbs, the bioreserve has long served as a haven for hikers, dog walkers, bird watchers, hunters, cross-country skiers, and other outdoors lovers. Provencher, a land protection specialist for ...
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