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 mi ...

(₄Be) has 11 known

isotopes Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

and 3 known

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

, but only one of these isotopes () is stable and a

primordial nuclide In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...

. As such, beryllium is considered a monoisotopic element. It is also a mononuclidic element, because its other isotopes have such short half-lives that none are primordial and their abundance is very low (

standard atomic weight The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, is ...

is ). Beryllium is unique as being the only monoisotopic element with both an even number of protons and an odd number of neutrons. There are 25 other monoisotopic elements but all have odd atomic numbers, and even numbers of neutrons. Of the 10 radioisotopes of beryllium, the most stable are with a half-life of million years and with a half-life of . All other radioisotopes have half-lives under , most under . The least stable isotope is , with a half-life of . The 1:1

neutron–proton ratio The neutron–proton ratio (N/Z ratio or nuclear ratio) of an atomic nucleus is the ratio of its number of neutrons to its number of protons. Among stable nuclei and naturally occurring nuclei, this ratio generally increases with increasing atomi ...

seen in stable isotopes of many light elements (up to

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

, and in elements with even atomic number up to

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

) is prevented in beryllium by the extreme instability of toward

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...

, which is favored due to the extremely tight binding of nuclei. The half-life for the decay of is only . Beryllium is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in neutron–proton ratio for such a light element. Nevertheless, this isotope, , has a half-life of million years, which indicates unusual stability for a light isotope with such a large neutron/proton imbalance. Other possible beryllium isotopes have even more severe mismatches in neutron and proton number, and thus are even less stable. Most in the universe is thought to be formed by cosmic ray nucleosynthesis from cosmic ray spallation in the period between 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 ...

and the formation of the solar system. The isotopes , with a half-life of , and are both cosmogenic nuclides because they are made on a recent timescale in the solar system by spallation, like . These two radioisotopes of beryllium in the atmosphere track the

sunspot Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...

cycle and solar activity, since this affects the magnetic field that shields the Earth from cosmic rays. The rate at which the short-lived is transferred from the air to the ground is controlled in part by the weather. decay in the sun is one of the sources of solar neutrinos, and the first type ever detected using the Homestake experiment. Presence of in sediments is often used to establish that they are fresh, i.e. less than about 3–4 months in age, or about two half-lives of . Be7fromcosmicrays

List of isotopes

, - , 'This isotope has not yet been observed; given data is inferred or estimated from periodic trends. , 4 , 1 , # , , p ?Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide. , ? , (1/2+)# , , , - , , 4 , 2 , ,
[] , proton emission, 2p , , 0+ , , , - , Produced in Big Bang nucleosynthesis, but not primordial, as it all quickly decayed to ⁷Li , 4 , 3 , , , Electron capture, ε , , 3/2− , Trace cosmogenic nuclide , , - , Intermediate product of

triple alpha process The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. Triple-alpha process in stars Helium accumulates in the cores of stars as a result of the proton–pro ...

stellar nucleosynthesis Stellar nucleosynthesis is the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a ...

as part of the path producing ¹²C , 4 , 4 , ,
[] , α , , 0+ , , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , α , , 2+ , , , - , , 4 , 5 , , colspan=3 align=center, Stable , 3/2− , 1 , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , ,
[] , , , 3/2− , , , - , Beryllium-10, , 4 , 6 , , , Beta decay, β⁻ , , 0+ , Trace , , - , rowspan=3, Has 1 halo nucleus, halo neutron , rowspan=3, 4 , rowspan=3, 7 , rowspan=3, , rowspan=3, , β⁻ () , , rowspan=3, 1/2+ , rowspan=3, , rowspan=3, , - , β⁻α () , , - , β⁻p () , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , ,
[] , IT ? , ? , 3/2− , , , - , rowspan=2, , rowspan=2, 4 , rowspan=2, 8 , rowspan=2, , rowspan=2, , β⁻ () , , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻n () , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , IT , , 0+ , , , - , , 4 , 9 , , , n ? , ? , (1/2−) , , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , , , (5/2+) , , , - , rowspan=5, Has 4 halo neutrons , rowspan=5, 4 , rowspan=5, 10 , rowspan=5, , rowspan=5, , β⁻n () , , rowspan=5, 0+ , rowspan=5, , rowspan=5, , - , β⁻ (> ) , , - , β⁻2n () , , - , β⁻t () , , - , β⁻α (< ) , , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , , , (2+) , , , - , , 4 , 11 , , , n , , (5/2+) , , , - , , 4 , 12 , ,
[] , 2n , , 0+ , ,

Decay chains

Most isotopes of beryllium within the proton/neutron nuclear drip line, drip lines decay via beta decay and/or a combination of beta decay and

or neutron emission. However, decays only via

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...

, a phenomenon to which its unusually long half-life may be attributed. Notably, its half-life can be artificially lowered by 0.83% via endohedral enclosure (⁷Be@C₆₀). Also anomalous is , which decays via alpha decay to . This alpha decay is often considered fission, which would be able to account for its extremely short half-life. :

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Notes

References

{{Authority control Beryllium