Isotopes of lithium

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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 (5332.3312(3) keV for ⁶Li and 5606.4401(6) keV for ⁷Li) when compared with the adjacent lighter and heavier elements, helium (7073.9156(4) keV for helium-4) and beryllium (6462.6693(85) keV for beryllium-9). The longest-lived radioisotope of lithium is ⁸Li, which has a half-life of just 838.7(3) milliseconds. ⁹Li has a half-life of 178.2(4) ms, and ¹¹Li has a half-life of 8.75(6) ms. 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 91(9) yoctoseconds (9.1(9)×10⁻²³ s), 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 10⁻⁹ 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.^[4] 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).^[5]