Isotopes of Lithium - Lithium-7

Lithium-7

Lithium-7 is by far the most-common isotope of natural lithium, making up about 92.5 percent of the atoms. Any lithium-7 atom contains three protons, four neutrons, and three electrons, and it is a boson, which means that its total atomic spin is an integer, usually zero. In the Universe, because of its nuclear properties, lithium-7 is less-common than helium, beryllium, carbon, nitrogen, or oxygen, even though the latter four all have heavier nuclei than that of lithium.

The lithium that is left over from the production of (the desirable) lithium-6, which is enriched in lithium-7 and depleted in lithium-6, has been sold commercially, and some of it has been released into the environment. The relative abundance of lithium-7 as high as 35 percent greater than the natural value have 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. In the depleted lithium, the relative abundance of lithium-6 can be reduced to as little as 20 percent of its nominal value, giving an atomic mass for the dicharged lithium that can range from about 6.94 atomic mass units to about 7.00 a.m.u. Hence in this example, the isotopic composition of lithium can vary somewhat depending on its source. An accurate atomic mass for samples of lithium cannot be measured for all sources of lithium.

Lithium-7 finds one use 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, protons, and pions.