digplanet beta 1: Athena
Share digplanet:


Applied sciences






















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.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

626 news items

Huffington Post
Mon, 28 Sep 2015 07:48:45 -0700

Lynne Twist, a philanthropist and author of The Soul of Money, believes that generosity flows out of gratitude, as she explains in this short film by acclaimed filmmaker Louie Schwartzberg. This is one of 16 videos in Schwartzberg's "Gratitude Revealed ...

The Creators Project (blog)

The Creators Project (blog)
Thu, 01 Oct 2015 08:00:00 -0700

While Brazil is known for its luscious natural abundance through its forests and beaches, the fifth largest country in area has its own share of environmental issues. São Paulo, Brazil's most populated metropolitan center, kills more people through its ...

Chicago Daily Herald

Chicago Daily Herald
Fri, 25 Sep 2015 03:52:30 -0700

"It represents a sense of goodness, natural abundance and old values that people think are good," said Cindy Ott, a scholar and author of "Pumpkin: The Curious History of an American Icon." Which is why, perhaps, pumpkin spice lattes bring equal parts ...

Huffington Post

Huffington Post
Tue, 29 Sep 2015 15:41:15 -0700

"A little goes a long way" is usually the mantra of the travel companies encouraging clients to take advantage of Greece, this economically-beleaguered but scenic and hospitable country. I notice here on Aegina Island that huge tourist coaches are on ...

VUE Weekly

VUE Weekly
Thu, 01 Oct 2015 10:34:08 -0700

And so you start to realize the power of these narratives: the narratives of endless frontiers, of infinite natural abundance from which we can extract infinitely. And you start realizing how many different ways they're reflected in our culture, it ...

Monroe News Star

Monroe News Star
Tue, 29 Sep 2015 12:07:30 -0700

“It represents a sense of goodness, natural abundance and old values that people think are good,” said Cindy Ott, a scholar and author of “Pumpkin: The Curious History of an American Icon.” Which is why, perhaps, pumpkin spice lattes bring equal parts ...


Mon, 28 Sep 2015 02:11:15 -0700

The state is the perfect host for the foodie festival thanks to its natural abundance and the enthusiasm of local producers to supply the best food and drink possible. The biennial festival attracts around 50,000 people and is a journey of South ...
Richmond Times-Dispatch
Sun, 27 Sep 2015 19:44:00 -0700

An isotopically-enriched, boron-containing compound comprising two or more boron atoms and at least one fluorine atom, wherein at least one of the boron atoms contains a desired isotope of boron in a concentration or ratio greater than a natural ...

Oops, we seem to be having trouble contacting Twitter

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!

Searchlight Group

Digplanet also receives support from Searchlight Group. Visit Searchlight