Isotopes of beryllium

Isotopes of beryllium (4Be)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
7Be trace 53.22 d ε 7Li
8Be synth 8.2×10−17 s[n 1] α 4He
9Be 100% stable
10Be trace 1.387×106 y β− 10B
Standard atomic weight Ar°(Be)

Beryllium (4Be) has 11 known isotopes and 3 known isomers, but only one of these isotopes (9
Be) is stable and a primordial nuclide. 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. Beryllium is unique as being the only monoisotopic element with an even number of protons (even atomic number) and also has an odd number of neutrons;[2] the 25 other monoisotopic elements all have odd numbers of protons (odd atomic number), and even of neutrons, so the total mass number is still odd.

Of the 10 radioisotopes of beryllium, the most stable are 10
Be with a half-life of 1.387 million years and 7
Be with a half-life of 53.22 days. All other radioisotopes have half-lives under 15 s, most under 30 milliseconds.

The 1:1 neutron–proton ratio seen in stable isotopes of many light elements (up to oxygen, and in elements with even atomic number up to calcium) is prevented in beryllium by the extreme instability of 8
Be toward splitting into two 4
He nuclei, which may be seen either alpha decay or a type of fission; in any case the half-life is only 8.2×10−17 s, short enough to normally be considered unbound. This, as with the relative instability of all lithium, beryllium, and boron isotopes, is favored due to the extremely tight binding of the helium-4 nucleus.

Beryllium is prevented from having a stable isotope with 4 protons and 6 neutrons by the very lopsided neutron–proton ratio for such a light element. Nevertheless, this isotope, beryllium-10, has a half-life above a million years and a decay energy less than 1 MeV, which indicates unusual stability given that condition.

Most beryllium present in the universe is thought to be formed by cosmic ray nucleosynthesis from cosmic ray spallation in the period between the Big Bang and the formation of the Solar System. The isotopes 7
Be and 10
Be are both cosmogenic nuclides because they are made, in the Solar System, continually at the rate they decay by spallation,[4] as is carbon-14.

  1. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. ^ a b "Standard Atomic Weights: Beryllium". CIAAW. 2013.
  3. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. ^ Cite error: The named reference Pol16 was invoked but never defined (see the help page).


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