Isotopes of lithium

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Overview

Naturally occurring lithium (Li) (standard atomic mass: 6.941(2) u) is composed of two stable isotopes (Template:SimpleNuclide and Template:SimpleNuclide, the latter being the more abundant (92.5% natural abundance). Seven radioisotopes have been characterized, the most stable being Template:SimpleNuclide with a half-life of 838 ms and Template:SimpleNuclide with a half-life of 178.3 ms. All of the remaining radioactive isotopes have half-lives that are shorter than 8.6 ms. The shortest-lived isotope of lithium is Template:SimpleNuclide which decays through proton emission and has a half-life of 7.58043×10−23 s.

Template:SimpleNuclide is one of the primordial elements or, more properly, primordial isotopes, produced in Big Bang nucleosynthesis (a small amount of Template:SimpleNuclide 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 Template:SimpleNuclide is preferred to Template:SimpleNuclide, resulting in enrichment of the light isotope in processes of hyperfiltration and rock alteration.

Isotopes

Lithium-4

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 9.1×10−23 s. It can be formed as an intermediate in some nuclear fusion reactions.

Lithium-6

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

Lithium-7

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 Template:SimpleNuclide abundance may be reduced by as much as 80% of its normal value, giving the atomic mass a range from 6.94 u to more than 6.99 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.

Table

nuclide
symbol
Z(Template:SubatomicParticle) N(Template:SubatomicParticle)  
isotopic mass (u)
 
half-life nuclear
spin
representative
isotopic
composition
(mole fraction)
range of natural
variation
(mole fraction)
excitation energy
Template:SimpleNuclide 3 1 4.02719(23) 91(9)×10−24 s [6.03 MeV] 2-
Template:SimpleNuclide 3 2 5.01254(5) 370(30)×10−24 s [~1.5 MeV] 3/2-
Template:SimpleNuclide 3 3 6.015122795(16) STABLE 1+ [0.0759(4)] 0.07714-0.07225
Template:SimpleNuclide 3 4 7.01600455(8) STABLE 3/2- [0.9241(4)] 0.92275-0.92786
Template:SimpleNuclide 3 5 8.02248736(10) 840.3(9) ms 2+
Template:SimpleNuclide 3 6 9.0267895(21) 178.3(4) ms 3/2-
Template:SimpleNuclide 3 7 10.035481(16) 2.0(5)×10−21 s [1.2(3) MeV] (1-,2-)
Template:SimpleNuclide 200(40) keV 3.7(15)×10−21 s 1+
Template:SimpleNuclide 480(40) keV 1.35(24)×10−21 s 2+
Template:SimpleNuclide 3 8 11.043798(21) 8.75(14) ms 3/2-
Template:SimpleNuclide 3 9 12.05378(107)# <10 ns

Notes

  • 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 Template:SimpleNuclide abundance may be reduced by as much as 80% of its normal value, giving the atomic mass a range from 6.94 u to more than 6.99 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.
  • Template:SimpleNuclide has a Nuclear halo of two weakly linked neutrons, thus explaining an important difference in the radius.

References


Isotopes of helium Isotopes of lithium Isotopes of beryllium
Index to isotope pages · Table of nuclides



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