Isotopes of lithium

Isotopes of lithium

Naturally occurring lithium (Li) (standard atomic mass: 6.941(2) u) is composed of two stable isotopes (SimpleNuclide|Lithium|6 and SimpleNuclide|Lithium|7, the latter being the more abundant (92.5% natural abundance). Seven radioisotopes have been characterized, the most stable being SimpleNuclide|Lithium|8 with a half-life of val|838|u=ms and SimpleNuclide|Lithium|9 with a half-life of val|178.3|u=ms. All of the remaining radioactive isotopes have half-lives that are shorter than val|8.6|u=ms. The shortest-lived isotope of lithium is SimpleNuclide|Lithium|4 which decays through proton emission and has a half-life of val|7.58043|e=-23|u=s.

SimpleNuclide|Lithium|7 is one of the primordial elements or, more properly, primordial isotopes, produced in Big Bang nucleosynthesis (a small amount of SimpleNuclide|Lithium|6 is also produced in stars). Lithium isotopes fractionate substantially during a wide variety of natural processes, including mineral formation (chemical precipitation), metabolism, and ion exchange. Lithium ion substitutes for magnesium and iron in octahedral sites in clay minerals, where SimpleNuclide|Lithium|6 is preferred to SimpleNuclide|Lithium|7, resulting in enrichment of the light isotope in processes of hyperfiltration and rock alteration.


Colex Separation

Lithium-6 has a greater affinity for mercury than does Lithium-7. When a lithium-mercury amalgam is in contact with a lithium hydroxide solution, Lithium-6 preferentially concentrates in the amalgam, and Lithium-7 in the hydroxide.

This is the basis of the COLEX (Column exchange) separation method, in which a counter flow of amalgam and hydroxide passes through a cascade of stages. The Lithium-6 fraction is preferentially drained by the mercury, the Lithium-7 fraction flows preferentially with the hydroxide.

At the bottom of the column, the Lithium (enriched in Lithium-6) is separated from the amalgam, the mercury is recovered and reused with fresh feedstock. At the top, the lithium hydroxide solution is electrolyzed to liberate the Lithium-7 enriched fraction. The enrichment obtained with this method varies with the column length and the flow speed.

This method leads to mercury pollution lost in wastes, spills, and through evaporation.

Vacuum Distillation

Lithium is heated to a temperature of about 550 C in a vacuum. Lithium atoms evaporate from the liquid surface, and are collected on a cold surface positioned a few cm above the liquid surface. Lithium-6 atoms have a greater mean free path, they are collected preferentially.

The theoretical separation efficiency is about 8%. Multi-stage process may be used to obtain higher degrees of separation.


Lithium-4 contains 3 protons and one neutron. It is the shortest lived isotope of lithium. It decays by proton emission and has a half-life of val|9.1|e=-23|u=s. It can be formed as an intermediate in some nuclear fusion reactions.


Lithium-6 is valued as a source material for tritium production and as a neutron absorber in nuclear fusion. Natural lithium contains about 7.5 percent lithium-6. Large amounts of lithium-6 have been isotopically fractionated for use in nuclear weapons.


Some of the material remaining from the production of lithium-6, which is depleted in lithium-6 and enriched in lithium-7, is made commercially available, and some has been released into the environment. Relative lithium-7 abundances as high as 35.4% greater than the natural value have been measured in ground water from a carbonate aquifer underlying West Valley Creek, Pennsylvania (USA), down-gradient from a lithium processing plant. In depleted material, the relative SimpleNuclide|Lithium|6 abundance may be reduced by as much as 80% of its normal value, giving the atomic mass a range from val|6.94|u=u to more than val|6.99|u=u. As a result, the isotopic composition of lithium is highly variable depending on its source. An accurate relative atomic mass cannot be given representatively for all samples.

Lithium-7 is profoundly useful as a constituent of the solvent lithium fluoride in liquid-fluoride nuclear reactors. Indeed, the large neutron absorption cross-section of lithium-6 (941 barns, thermal) and the small neutron absorption cross section of lithium-7 (0.045 barns, thermal) make strict isotopic separation of lithium a requirement for fluoride reactor use.



* The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
* Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
* Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
* In depleted material, the relative SimpleNuclide|Lithium|6 abundance may be reduced by as much as 80% of its normal value, giving the atomic mass a range from val|6.94|u=u to more than val|6.99|u=u.
* Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
* Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
* has a Nuclear halo of two weakly linked neutrons, thus explaining an important difference in the radius.


* Isotope masses from [ Ame2003 Atomic Mass Evaluation] by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in "Nuclear Physics" A729 (2003).
* Isotopic compositions and standard atomic masses from [ Atomic weights of the elements. Review 2000 (IUPAC Technical Report)] . "Pure Appl. Chem." Vol. 75, No. 6, pp. 683-800, (2003) and [ Atomic Weights Revised (2005)] .
* Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
** Audi, Bersillon, Blachot, Wapstra. [ The Nubase2003 evaluation of nuclear and decay properties] , Nuc. Phys. A 729, pp. 3-128 (2003).
** National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the [ NuDat 2.1 database] (retrieved Sept. 2005).
** David R. Lide (ed.), Norman E. Holden in "CRC Handbook of Chemistry and Physics, 85th Edition", online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.

Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Isotopes du lithium — Le lithium (Li) d origine naturelle (masse atomique : 6.941(2) u) est présent dans la nature sous la forme de deux isotopes stables, 6Li et 7Li, ce dernier étant le plus abondant (92,5 %). Les deux isotopes ont une plus faible énergie… …   Wikipédia en Français

  • Lithium — (pronEng|ˈlɪθiəm) is a chemical element with the symbol Li and atomic number 3. It is a soft alkali metal with a silver white color. Under standard conditions, it is the lightest metal and the least dense solid element. Like all alkali metals,… …   Wikipedia

  • LITHIUM — Le lithium est un métal blanc et brillant lorsqu’il est fraîchement coupé. Il a été découvert, en 1817, par Johann August Arfvedson dans un silicate d’aluminium naturel: le pétalite. Jöns Jacob Berzelius donna au nouvel élément, de numéro… …   Encyclopédie Universelle

  • Lithium — Pour les articles homonymes, voir Lithium (homonymie). Lithium Hélium ← Lithium …   Wikipédia en Français

  • Isotopes de l'hélium — L hélium (He) (masse atomique standard: 4,002602(2) u) possède huit isotopes connus, mais seulement deux sont stables, l hélium 3 (3He) et l hélium 4 (4He). Tous les radioisotopes de l hélium ont une durée de vie courte, 6He, celui à la durée la… …   Wikipédia en Français

  • lithium — /lith ee euhm/, n. 1. Chem. a soft, silver white metallic element, the lightest of all metals, occurring combined in certain minerals. Symbol: Li; at. wt.: 6.939; at. no.: 3; sp. gr.: 0.53 at 20°C. 2. Pharm. the substance in its carbonate or… …   Universalium

  • Isotopes de l'hydrogène — Le protium, l isotope le pus commun de hydrogène, constitué d un proton et d un électron. Cas unique, c est le seul isotope stable sans neutron. L hydrogène (H) (masse atomique standard: 1,00782504(7) u) possède trois isotopes naturels, parfois… …   Wikipédia en Français

  • Isotopes of helium — Although there are eight known isotopes of helium (He) (standard atomic mass: 4.002602(2) u), only helium 3 (SimpleNuclide|Helium|3) and helium 4 (SimpleNuclide|Helium|4) are stable. In the Earth s atmosphere, there is one SimpleNuclide|Helium|3… …   Wikipedia

  • Isotopes of nitrogen — Natural Nitrogen (N) consists of two stable isotopes, nitrogen 14, which makes up the vast majority of naturally occurring nitrogen, and nitrogen 15. Fourteen radioactive isotopes (radioisotopes) have also been found so far, with atomic masses… …   Wikipedia

  • Abundances of the isotopes — ▪ Table Abundances of the isotopes element Z symbol A abundance   mass excess hydrogen 1 H 1 99.9885 7.289 2 0.0151 13.136 helium 2 He 3 0.000138 14.931 4 99.999863 2.425 lithium 3 Li 6 7.59 14.086 7 92.41 14.908 beryllium 4 Be 9 100  11.348… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”