7Li

7Li, or lithium-7, is one of the two stable isotopes of lithium. It has a mass number of 7 and accounts for the majority of natural lithium, about 92.5%, with the remainder mainly 6Li. Like all lithium nuclei, it consists of 3 protons and 4 neutrons. It is not radioactive and has an exceptionally long lifetime, effectively making it stable on geological timescales.

Nuclear properties of 7Li include a ground-state nuclear spin of I = 3/2 and a nonzero electric quadrupole moment, reflecting a non-spherical nuclear charge distribution. These features give rise to hyperfine structure in atomic spectra and enable certain spectroscopic and magnetic resonance applications. The magnetic dipole moment is significant, making 7Li detectable in various magnetic resonance techniques.

In nature and production, 7Li is produced in small amounts during Big Bang nucleosynthesis and through cosmic ray spallation. It is primarily extracted from mineral deposits (such as spodumene, petalite, and lepidolite) and from lithium-rich brines. The isotope split is important for industrial and scientific use because the high natural abundance of 7Li simplifies enrichment needs for specific applications.

Applications and uses include its role in nuclear magnetic resonance (NMR) spectroscopy, where 7Li NMR is used to study organolithium compounds and other lithium-containing species. The isotope’s spin properties, combined with its relatively high natural abundance, make it valuable for chemical analysis and materials research.

In cosmology and astrophysics, 7Li is central to discussions of lithium production in the early universe. The so-called lithium problem refers to discrepancies between predicted primordial 7Li abundance and what is observed in old stars, prompting ongoing research into nucleosynthesis and stellar processes.