lithium-11

Naturally occurring lithium (₃Li) is composed of two stable isotopes, lithium-6 (⁶Li) and lithium-7 (⁷Li), with the latter being far more abundant on Earth. Both of the natural isotopes have an unexpectedly low nuclear binding energy per nucleon ( for ⁶Li and for ⁷Li) when compared with the adjacent lighter and heavier elements, helium ( for helium-4) and beryllium ( for beryllium-9). The longest-lived radioisotope of lithium is ⁸Li, which has a half-life of just . ⁹Li has a half-life of , and ¹¹Li has a half-life of . All of the remaining isotopes of lithium have half-lives that are shorter than 10 nanoseconds. The shortest-lived known isotope of lithium is ⁴Li, which decays by proton emission with a half-life of about (), although the half-life of ³Li is yet to be determined, and is likely to be much shorter, like ²He (helium-2, diproton) which undergoes proton emission within s.

Both ⁷Li and ⁶Li are two of the primordial nuclides that were produced in the Big Bang, with ⁷Li to be 10⁻⁹ of all primordial nuclides, and ⁶Li around 10⁻¹³. A small percentage of ⁶Li is also known to be produced by nuclear reactions in certain stars. The isotopes of lithium separate somewhat during a variety of geological processes, including mineral formation (chemical precipitation and ion exchange). Lithium ions replace magnesium or iron in certain octahedral locations in clays, and lithium-6 is sometimes preferred over ⁷Li. This results in some enrichment of ⁶Li in geological processes.

In nuclear physics, ⁶Li is an important isotope, because when it is bombarded with neutrons, tritium is produced.

Both ⁶Li and ⁷Li isotopes show nuclear magnetic resonance effect, despite being quadrupolar (with nuclear spins of 1+ and 3/2−). ⁶Li has sharper lines, but due to its lower abundance requires a more sensitive NMR-spectrometer. ⁷Li is more abundant, but has broader lines because of its larger nuclear spin. The range of chemical shifts is the same of both nuclei and lies within +10 (for LiNH₂ in liquid NH₃) and −12 (for Li+ in fulleride).

List of isotopes

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, Discovery of this isotope is unconfirmed
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, p ?Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide.
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, One of the few stable even and odd atomic nuclei#Odd proton, odd neutron, odd-odd nuclei
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, colspan="3" style="text-align:center;", Stable
, 1+
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, Produced in Big Bang nucleosynthesis and by cosmic ray spallation
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, colspan="3" style="text-align:center;", Stable
, 3/2−
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, β⁻
, Immediately decays into two α-particles for a net reaction of ⁸Li → 2⁴He + e⁻
, 2+
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, rowspan="2" style="text-align:right" , 3
, rowspan="2" style="text-align:right" , 6
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, β⁻n ()
, Immediately decays into two α-particles for a net reaction of ⁹Li → 2⁴He + ¹n + e⁻
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, β⁻ ()
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, rowspan=7, Has 2 halo nucleus, halo neutrons
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, β⁻n ()
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, β⁻ ()
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, β⁻2n ()
,
, -
, β⁻3n ()
, Immediately decays into two ⁴He atoms for a net reaction of ¹¹Li → 2⁴He + 3¹n + e⁻
, -
, β⁻α ()
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, β⁻d ()
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, β⁻t ()
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Isotope separation

Colex separation

Lithium-6 has a greater affinity than lithium-7 for the Chemical element, element mercury (element), mercury. When an amalgam of lithium and mercury is added to solutions containing lithium hydroxide, the lithium-6 becomes more concentrated in the amalgam and the lithium-7 more in the hydroxide solution.

The colex (column exchange) separation method makes use of this by passing a counter-flow of amalgam and hydroxide through a cascade of stages. The fraction of lithium-6 is preferentially drained by the mercury, but the lithium-7 flows mostly with the hydroxide.
At the bottom of the column, the lithium (enriched with lithium-6) is separated from the amalgam, and the mercury is recovered to be reused with fresh raw material. At the top, the lithium hydroxide solution is electrolyzed to liberate the lithium-7 fraction. The enrichment obtained with this method varies with the column length and the flow speed.

Other methods

In the vacuum distillation technique, lithium is heated to a temperature of about in a vacuum. Lithium atoms evaporate from the liquid surface and are collected on a cold surface positioned a few centimetres above the liquid surface. Since lithium-6 atoms have a greater mean free path, they are collected preferentially. The theoretical separation efficiency of this method is about 8.0 percent. A multistage process may be used to obtain higher degrees of separation.

The isotopes of lithium, in principle, can also be separated through electrochemical method and distillation chromatography, which are currently in development.

Lithium-3

Lithium-3, also known as the triproton, would consist of three protons and zero neutrons. It was reported as proton unbound in 1969, but this result was not accepted and its existence is thus unproven. No other resonances attributable to have been reported, and it is expected to decay by prompt proton emission (much like the diproton, ).

Lithium-4

Lithium-4 contains three protons and one neutron. It is the shortest-lived known isotope of lithium, with a half-life of () and decays by proton emission to helium-3. Lithium-4 can be formed as an intermediate in some nuclear fusion reactions.

Lithium-5

Lithium-5 is very short-lived with a half-life of 370(30) yoctoseconds, decaying via proton emission to helium-4. It is formed as an intermediate in the fusion of deuterium and helium-3:

$^2\mathrm + ^3\mathrm \longrightarrow ^5\mathrm^ \longrightarrow ^4\mathrm + p + 18.4\ \mathrm$

The reaction is greatly enhanced by the existence of a resonance. Lithium-5, which has a natural spin state of −3/2 at the 0 MeV ground state, has a +3/2 excited spin state at 16.66 MeV. Because the reaction creates lithium-5 nuclei with an energy level close to this state, it happens more frequently. A symmetrical resonance in the helium-5 nucleus makes the deuterium–tritium fusion reaction the most favourable known.

Lithium-6

Lithium-6 is valuable as the source material for the production of tritium (hydrogen-3) and as an absorber of neutrons in nuclear fusion reactions. Between 1.9% and 7.8% of terrestrial lithium in normal materials consists of lithium-6, with the rest being lithium-7. Large amounts of lithium-6 have been separated out for placing into thermonuclear weapons. The separation of lithium-6 has by now ceased in the large thermonuclear powers, but stockpiles of it remain in these countries.

The deuterium–tritium fusion reaction has been investigated as a possible energy source, as it is currently the only fusion reaction with sufficient energy output for feasible implementation. In this scenario, lithium enriched in lithium-6 would be required to generate the necessary quantities of tritium. Mineral and brine lithium resources are a potential limiting factor in this scenario, but seawater can eventually also be used. Pressurized heavy-water reactors such as the CANDU produce small quantities of tritium in their coolant/moderator from neutron absorption and this is sometimes extracted as an alternative to the use of lithium-6.

Lithium-6 is one of only four stable isotopes with a spin of 1, the others being deuterium, boron-10, and nitrogen-14, and has the smallest nonzero nuclear electric quadrupole moment of any stable nucleus.

In 2025, researchers from ETH Zürich and Texas A&M University introduced a mercury-free method for isolating lithium-6, providing an alternative to the COLEX process, which uses toxic liquid mercury. This technique was discovered by accident during water purification research and utilized zeta-vanadium oxide (ζ-V2O5) to selectively trap lithium-6 ions, which could be a crucial step in scaling up the production of fusion-grade lithium-6, potentially unlocking more cost-effective and safer ways to isolate lithium for nuclear fusion reactors.

Lithium-7

Lithium-7 is by far the most abundant isotope of lithium, making up between 92.2% and 98.1% of all terrestrial lithium. A lithium-7 atom contains three protons, four neutrons, and three electrons. Because of its nuclear properties, lithium-7 is less common than helium, carbon, nitrogen, or oxygen in the Universe, even though the latter three all have heavier nuclei. The Castle Bravo thermonuclear test greatly exceeded its expected yield due to incorrect assumptions about the nuclear properties of lithium-7.

The industrial production of lithium-6 results in a waste product which is enriched in lithium-7 and depleted in lithium-6. This material has been sold commercially, and some of it has been released into the environment. A relative abundance of lithium-7, as high as 35 percent greater than the natural value, has been measured in the ground water in a carbonate aquifer underneath the West Valley Creek in Pennsylvania, which is downstream from a lithium processing plant. The isotopic composition of lithium in normal materials can vary somewhat depending on its origin, which determines its relative atomic mass in the source material. An accurate relative atomic mass for samples of lithium cannot be measured for all sources of lithium.

Lithium-7 is used as a part of the molten lithium fluoride in molten-salt reactors: liquid-fluoride nuclear reactors. The large neutron absorption cross section of lithium-6 (about 940 barns)
as compared with the very small neutron cross section of lithium-7 (about 45 millibarns) makes high separation of lithium-7 from natural lithium a strong requirement for the possible use in lithium fluoride reactors.

Lithium-7 hydroxide is used for alkalizing of the coolant in pressurized water reactors.

Some lithium-7 has been produced, for a few picoseconds, which contains a lambda particle in its nucleus, whereas an atomic nucleus is generally thought to contain only neutrons and protons.

Lithium-8

Lithium-8 has been proposed as a source of 6.4 MeV electron antineutrinos generated by the inverse beta decay to beryllium-8. The ISODAR particle physics collaboration describes a scheme to generate lithium-8 for immediate decay by bombarding stable lithium-7 with 60 MeV protons created by a cyclotron particle accelerator.

Lithium-11

Lithium-11 is a halo nucleus consisting of a lithium-9 core surrounded by two loosely-bound neutrons; both neutrons must be present in order for this system to be bound, which has led to the description as a " Borromean nucleus". While the proton root-mean-square radius of ¹¹Li is , its neutron radius is much larger at ; for comparison, the corresponding figures for ⁹Li are for the protons and for the neutrons. It decays by beta emission and neutron emission to , , or (see tables above and below). Having a magic number of 8 neutrons, lithium-11 sits on the first of five known islands of inversion, which explains its longer half-life compared to adjacent nuclei.

Lithium-12

Lithium-12 has a considerably shorter half-life. It decays by neutron emission into , which decays as mentioned above.

Decay chains

While β⁻ decay into isotopes of beryllium (often combined with single- or multiple-neutron emission) is predominant in heavier isotopes of lithium, and decay via neutron emission into and respectively due to their positions beyond the neutron drip line. Lithium-11 has also been observed to decay via multiple forms of fission. Isotopes lighter than decay into isotopes of helium exclusively by proton emission, as they are beyond the proton drip line. The decay modes of the two isomers of are unknown.
:$\begin\\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \end$

See also

* Cosmological lithium problem
*
* Halo nucleus
*

References

External links

{{Navbox element isotopes

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Lithium