6Li

6Li is a stable isotope of lithium with atomic number 3 and mass number 6. It accounts for about 7.5% of naturally occurring lithium, with the remainder mainly 7Li. Lithium is found in minerals and seawater, and its isotopic composition is routinely measured in geochemistry and materials science.

The nucleus of 6Li consists of three protons and three neutrons. It is stable and notable for its use in neutron detection because it has a large cross section for absorbing thermal neutrons. The primary neutron-induced reaction is 6Li + n → 4He + 3H (triton), releasing about 4.8 MeV of energy. This property underpins several detector technologies and shielding materials that rely on lithium-6.

6Li is produced in small amounts during Big Bang nucleosynthesis and is continually created by cosmic ray spallation and in stellar environments. Its natural abundance is modest compared with 7Li, and enrichment of 6Li is common for applications requiring its neutron-capturing properties or specific nuclear reactions.

In applications, 6Li is used in neutron detectors, including lithium-containing scintillators and glass, as well as in fusion research where lithium-6 participates in breeding tritium in breeding blankets. Enriched Li-6 compounds, such as LiD, are used in certain fusion and experimental setups. In addition, measurements of the 6Li/7Li ratio aid studies of cosmic ray history, nucleosynthesis, and planetary geology.