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Naturally occurring lithium (3Li) is composed of two
stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...
, 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 In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...
( for lithium-6 and for lithium-7) when compared with the adjacent lighter and heavier elements, helium ( for helium-4) and
beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form ...
( for beryllium-9). The longest-lived
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
of lithium is lithium-8, which has a
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
of just . Lithium-9 has a half-life of , and lithium-11 has a half-life of . All of the remaining isotopes of lithium have half-lives that are shorter than 10
nanoseconds A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or 10 seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...
. The shortest-lived known isotope of lithium is lithium-4, which decays by
proton emission Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case t ...
with a half-life of about (), 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 s. Lithium-7 and lithium-6 are two of the primordial nuclides that were produced in the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
, 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 Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
). 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 The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...
, tritium is produced.


List of isotopes

, - , Discovery of this isotope is unconfirmed , style="text-align:right" , 3 , style="text-align:right" , 0 , # , , p ?Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide. , ? , 3/2−# , , , - , , style="text-align:right" , 3 , style="text-align:right" , 1 , ,
[] , p , Helium-3, , 2− , , , - , , style="text-align:right" , 3 , style="text-align:right" , 2 , ,
[] , p , Helium-4, , 3/2− , , , - , One of the few stable odd-odd nuclei , style="text-align:right" , 3 , style="text-align:right" , 3 , , colspan="3" style="text-align:center;", Stable , 1+ , style="text-align:center" colspan="2", ref name="Atomic Weight of Lithiumb"> , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , IT , , 0+ , , , - , Produced in
Big Bang nucleosynthesis In physical cosmology, Big Bang nucleosynthesis (abbreviated BBN, also known as primordial nucleosynthesis) is the production of nuclei other than those of the lightest isotope of hydrogen (hydrogen-1, 1H, having a single proton as a nucleus) du ...
and by
cosmic ray spallation Cosmic ray spallation, also known as the x-process, is a set of naturally occurring nuclear reactions causing nucleosynthesis; it refers to the formation of chemical elements from the impact of cosmic rays on an object. Cosmic rays are highly ener ...
, style="text-align:right" , 3 , style="text-align:right" , 4 , , colspan="3" style="text-align:center;", Stable , 3/2− , colspan="2" style="text-align:center", ref name="Atomic Weight of Lithiumb" /> , - , , style="text-align:right" , 3 , style="text-align:right" , 5 , , , β , Immediately decays into two α-particles for a net reaction of 8Li → 24He + e , 2+ , , , - , rowspan="2", , rowspan="2" style="text-align:right" , 3 , rowspan="2" style="text-align:right" , 6 , rowspan="2", , rowspan="2", , βn () , Immediately decays into two α-particles for a net reaction of 9Li → 24He + 1n + e , rowspan="2", 3/2− , rowspan="2", , rowspan="2", , - , β () , , - , , style="text-align:right" , 3 , style="text-align:right" , 7 , ,
[] , n , , (1−, 2−) , , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , IT , , 1+ , , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , ,
[] , IT , , 2+ , , , - , rowspan=7, Has 2 halo nucleus, halo neutrons , rowspan=7 style="text-align:right" , 3 , rowspan=7 style="text-align:right" , 8 , rowspan=7, , rowspan=7, , βn () , , rowspan=7, 3/2− , rowspan=7, , rowspan=7, , - , β () , , - , β2n () , , - , β3n () , Immediately decays into two 4He atoms for a net reaction of 11Li → 24He + 31n + e , - , βα () , , - , βd () , , - , βt () , , - , , style="text-align:right" , 3 , style="text-align:right" , 9 , , , n ? , ? , (1−, 2−) , , , - , , style="text-align:right" , 3 , style="text-align:right" , 10 , ,
[] , 2n , , 3/2−# , ,


Isotope separation


Colex separation

Lithium-6 has a greater affinity than lithium-7 for the Chemical element, element mercury (element), mercury. When an amalgam of lithium and mercury is added to solutions containing lithium hydroxide, the lithium-6 becomes more concentrated in the amalgam and the lithium-7 more in the hydroxide solution. The colex (column exchange) separation method makes use of this by passing a counter-flow of amalgam and hydroxide through a cascade of stages. The
fraction A fraction (from la, fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight ...
of lithium-6 is preferentially drained by the mercury, but the lithium-7 flows mostly with the hydroxide. At the bottom of the column, the lithium (enriched with lithium-6) is separated from the amalgam, and the mercury is recovered to be reused with fresh
raw material A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods, finished goods, energy, or intermediate materials that are feedstock for future finished products. As feedst ...
. At the top, the lithium hydroxide solution is
electrolyzed In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from na ...
to liberate the lithium-7 fraction. The enrichment obtained with this method varies with the column length and the flow speed.


Vacuum distillation

Lithium is heated to a temperature of about in a vacuum. Lithium atoms evaporate from the liquid surface and are collected on a cold surface positioned a few centimetres above the liquid surface. Since lithium-6 atoms have a greater mean free path, they are collected preferentially. The theoretical separation efficiency is about 8.0 percent. A multistage process may be used to obtain higher degrees of separation.


Lithium-3

Lithium-3, also known as the triproton, would consist of three protons and zero
neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...
. It was reported as proton unbound in 1969, but this result was not accepted and its existence is thus unproven. No other
resonances Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillat ...
attributable to have been reported, and it is expected to decay by prompt
proton emission Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case t ...
(much like the diproton, ).


Lithium-4

Lithium-4 contains three protons and one neutron. It is the shortest-lived known isotope of lithium, with a half-life of () and decays by proton emission to
helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the ...
. Lithium-4 can be formed as an intermediate in some nuclear fusion reactions.


Lithium-6

Lithium-6 is valuable as the source material for the production of tritium (hydrogen-3) and as an absorber of neutrons in nuclear fusion reactions. Between 1.9% and 7.8% of terrestrial lithium in normal materials consists of lithium-6, with the rest being lithium-7. Large amounts of lithium-6 have been separated out for placing into thermonuclear weapons. The separation of lithium-6 has by now ceased in the large
thermonuclear Thermonuclear fusion is the process of atomic nuclei combining or “fusing” using high temperatures to drive them close enough together for this to become possible. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the re ...
powers, but stockpiles of it remain in these countries. The deuterium–tritium fusion reaction has been investigated as a possible energy source, as it is currently the only fusion reaction with sufficient energy output for feasible implementation. In this scenario, lithium enriched in lithium-6 would be required to generate the necessary quantities of tritium. Mineral and brine lithium resources are a potential limiting factor in this scenario, but seawater can eventually also be used. Pressurized heavy-water reactors such as the
CANDU The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...
produce small quantities of tritium in their coolant/moderator from neutron absorption and this is sometimes extracted as an alternative to the use of Lithium-6. Lithium-6 is one of only three stable isotopes with a
spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...
of 1, the others being deuterium and nitrogen-14, and has the smallest nonzero nuclear electric quadrupole moment of any stable nucleus.


Lithium-7

Lithium-7 is by far the most abundant isotope of lithium, making up between 92.2% and 98.1% of all terrestrial lithium. A lithium-7 atom contains three protons, four neutrons, and three electrons. Because of its nuclear properties, lithium-7 is less common than helium, carbon, nitrogen, or oxygen in the Universe, even though the latter three all have heavier nuclei. The industrial production of lithium-6 results in a waste product which is enriched in lithium-7 and depleted in lithium-6. This material has been sold commercially, and some of it has been released into the environment. A relative abundance of lithium-7, as high as 35 percent greater than the natural value, has 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. The isotopic composition of lithium in normal materials can vary somewhat depending on its origin, which determines its relative atomic mass in the source material. An accurate relative atomic mass for samples of lithium cannot be measured for all sources of lithium. Lithium-7 is used as a part of the molten
lithium fluoride Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid, that transitions to white with decreasing crystal size. Although odorless, lithium fluoride has a bitter-saline taste. Its structure is analogous to ...
in
molten salt reactors A molten salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a molten salt mixture. Only two MSRs have ever operated, both research reactors in the United States. The 1950's Ai ...
: 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 A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan and Canada). In a PWR, the primary coolant (water) is ...
. Some lithium-7 has been produced, for a few picoseconds, which contains a
lambda particle The lambda baryons (Λ) are a family of subatomic hadron particles containing one up quark, one down quark, and a third quark from a higher flavour generation, in a combination where the quantum wave function changes sign upon the flavour of an ...
in its nucleus, whereas an atomic nucleus is generally thought to contain only neutrons and protons.


Lithium-8

Lithium-8 has been proposed as a source of 6.4 MeV electron antineutrinos generated by the inverse beta decay to Beryllium-8. The ISODAR particle physics collaboration describes a scheme to generated Lithium-8 for immediate decay by bombarding stable Lithium-7 with 60 MeV protons created by a
cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...
.


Lithium-11

Lithium-11 is thought to possess a
halo nucleus In nuclear physics, an atomic nucleus is called a halo nucleus or is said to have a nuclear halo when it has a core nucleus surrounded by a "halo" of orbiting protons or neutrons, which makes the radius of the nucleus appreciably larger than that ...
consisting of a core of three protons and eight neutrons, two of which are in a nuclear halo. It has an exceptionally large cross-section of 3.16 fm2, comparable to that of . It decays by
beta emission In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For exa ...
and
neutron emission Neutron emission is a mode of radioactive decay in which one or more neutrons are ejected from a nucleus. It occurs in the most neutron-rich/proton-deficient nuclides, and also from excited states of other nuclides as in photoneutron emission and ...
to , , or (see tables above and below).


Lithium-12

Lithium-12 has a considerably shorter half-life. It decays by neutron emission into , which decays as mentioned above.


Decay chains

While β decay into
isotopes of beryllium Beryllium (4Be) has 11 known isotopes and 3 known isomers, but only one of these isotopes () is stable and a primordial nuclide. As such, beryllium is considered a monoisotopic element. It is also a mononuclidic element, because its other is ...
(often combined with single- or multiple-neutron emission) is predominant in heavier isotopes of lithium, and decay via neutron emission into and respectively due to their positions beyond the neutron drip line. Lithium-11 has also been observed to decay via multiple forms of fission. Isotopes lighter than decay exclusively by proton emission, as they are beyond the proton drip line. The decay modes of the two isomers of are unknown. :\begin\\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \ce \\ \end


See also

* Cosmological lithium problem * *
Halo nucleus In nuclear physics, an atomic nucleus is called a halo nucleus or is said to have a nuclear halo when it has a core nucleus surrounded by a "halo" of orbiting protons or neutrons, which makes the radius of the nucleus appreciably larger than that ...
*


References


External links

{{Navbox element isotopes Lithium Lithium