Isotopes of lithium

Naturally occurring lithium (₃Li) is composed of two stable isotopes, lithium-6 and lithium-7, 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 lithium-6 and 5606.4401(6) keV for lithium-7) 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 lithium-8, which has a half-life of just 838.7(3) milliseconds. Lithium-9 has a half-life of 178.2(4) ms, and lithium-11 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 lithium-4, 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 lithium-3 is yet to be determined, and is likely to be much shorter, like helium-2 (diproton) which undergoes proton emission within 10⁻⁹ s.

Lithium-7 and lithium-6 are two of the primordial nuclides that were produced in the Big Bang, with lithium-7 to be 10⁻⁹ of all primordial nuclides, and lithium-6 around 10⁻¹³. A small percentage of lithium-6 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 lithium-7. This results in some enrichment of lithium-6 in geological processes.

Lithium-6 is an important isotope in nuclear physics, 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).