Lithium Isotopes - Radioactive Decay and Half-Life

Facts About the Isotopes of Lithium

Lithium Atom, illustration
CAROL & MIKE WERNER/SCIENCE PHOTO LIBRARY / Getty Images

All lithium atoms have three protons but could have between zero and nine neutrons. There are ten known isotopes of lithium, ranging from Li-3 to Li-12. Many lithium isotopes have multiple decay paths depending on the overall energy of the nucleus and its total angular momentum quantum number. Because the natural isotope ratio varies considerably depending where a lithium sample was obtained, the standard atomic weight of the element is best expressed as a range (i.e. 6.9387 to 6.9959) rather than a single value.

Lithium Isotope Half-Life and Decay

This table lists the known isotopes of lithium, their half-life, and type of radioactive decay. Isotopes with multiple decay schemes are represented by a range of half-life values between the shortest and longest half-life for that type of decay.

IsotopeHalf-LifeDecay
Li-3--p
Li-44.9 x 10-23 seconds - 8.9 x 10-23 secondsp
Li-55.4 x 10-22 secondsp
Li-6Stable
7.6 x 10-23 seconds - 2.7 x 10-20 seconds
N/A
α, 3H, IT, n, p possible
Li-7Stable
7.5 x 10-22 seconds - 7.3 x 10-14 seconds
N/A
α, 3H, IT, n, p possible
Li-80.8 seconds
8.2 x 10-15 seconds
1.6 x 10-21 seconds - 1.9 x 10-20 seconds
β-
IT
n
Li-90.2 seconds
7.5 x 10-21 seconds
1.6 x 10-21 seconds - 1.9 x 10-20 seconds
β-
n
p
Li-10unknown
5.5 x 10-22 seconds - 5.5 x 10-21 seconds
n
γ
Li-118.6 x 10-3 secondsβ-
Li-121 x 10-8 secondsn

 

α
β-
γ
3H
IT
n
p
alpha decay
beta- decay
gamma photon
hydrogen-3 nucleus or tritium nucleus
isomeric transition
neutron emission
proton emission

 

Table Reference: International Atomic Energy Agency ENSDF database (Oct 2010)

Lithium-3

Lithium-3 becomes helium-2 via proton emission.

Lithium-4

Lithium-4 decays almost instantly (yoctoseconds) via proton emission into helium-3. It also forms as an intermediate in other nuclear reactions.

Lithium-5

Lithium-5 decays via proton emission into helium-4.

Lithium-6

Lithium-6 is one of the two stable lithium isotopes. It does, however, have a metastable state (Li-6m) that undergoes an isomeric transition to lithium-6.

Lithium-7

Lithium-7 is the second stable lithium isotope and the most abundant. Li-7 accounts for about 92.5 percent of natural lithium. Because of lithium's nuclear properties, it is less abundant in the universe than helium, beryllium, carbon, nitrogen, or oxygen.

Lithium-7 is used in the molten lithium fluoride of molten salt reactors. Lithium-6 has a large neutron-absorption cross section (940 barns) compared with that of lithium-7 (45 millibarns), so lithium-7 must be separated from the other natural isotopes before use in the reactor. Lithium-7 is also used to alkalize coolant in pressurized water reactors. Lithium-7 has been known to briefly contain lambda particles in its nucleus (as opposed to the usual complement of just protons and neutrons).

Lithium-8

Lithium-8 decays into beryllium-8.

Lithium-9

Lithium-9 decays into beryllium-9 via beta-minus decay about half the time and by neutron emission the other half of the time.

Lithium-10

Lithium-10 decays via neutron emission into Li-9. Li-10 atoms may exist in at least two metastable states: Li-10m1 and Li-10m2.

Lithium-11

Lithium-11 is believed to have a halo nucleus. What this means is each atom has a core containing three protons and eight neutrons, but two of the neutrons orbit the protons and other neutrons. Li-11 decays via beta emission into Be-11.

Lithium-12

Lithium-12 rapidly decays via neutron emission into Li-11.

Sources

  • Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties". Chinese Physics C. 41 (3): 030001. doi:10.1088/1674-1137/41/3/030001
  • Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford University Press. pp. 234–239. ISBN 978-0-19-850340-8.
  • Holden, Norman E. (January–February 2010). "The Impact of Depleted 6Li on the Standard Atomic Weight of Lithium". Chemistry International. International Union of Pure and Applied Chemistry. Vol. 32 No. 1.
  • Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305
  • Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references". Chinese Physics C. 41 (3): 030003–1—030003–442. doi:10.1088/1674-1137/41/3/030003