Isotopes of beryllium

Beryllium (₄Be) has 11 known isotopes and 3 known isomers, but only one of these isotopes (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 (standard atomic weight 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 Be with a half-life of million yearsTemplate:Refn and Be with a half-life of . All other radioisotopes have half-lives under , most under . The least stable isotope is Be, with a half-life of .

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 Be toward alpha decay, which is favored due to the extremely tight binding of He nuclei. The half-life for the decay of Be is only .

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, Be, has a half-life of million years,Template:Refn 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 Be 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 Be, with a half-life of , and Be are both cosmogenic nuclides because they are made on a recent timescale in the Solar System by spallation, like C.

List of isotopes

Template:Isotopes table |-id=Beryllium-6 | Be |4 |2 | |
[] | 2p | He | 0+ | |- | Be |4 |3 | | | ε | Li | 3/2− | Trace |- | Be |4 |4 | |
[] | α | He | 0+ | |-id=Beryllium-8m | style="text-indent:1em" | Be | colspan="3" style="text-indent:2em" | | | α | He | 2+ | |-id=Beryllium-9 | Be |4 |5 | | colspan=3 align=center|Stable | 3/2− | 1 |-id=Beryllium-9m | style="text-indent:1em" | Be | colspan="3" style="text-indent:2em" | |
[] | | | 3/2− | |- | Be |4 |6 | | Template:Refn | β⁻ | B | 0+ | Trace |-id=Beryllium-11 | rowspan=3|Be | rowspan=3|4 | rowspan=3|7 | rowspan=3| | rowspan=3| | β⁻ () | B | rowspan=3|1/2+ | rowspan=3| |- | β⁻α () | Li |- | β⁻p () | Be |-id=Beryllium-11m | style="text-indent:1em" | Be | colspan="3" style="text-indent:2em" | |
[] | IT ? | Be ? | 3/2− | |-id=Beryllium-12 | rowspan=2|Be | rowspan=2|4 | rowspan=2|8 | rowspan=2| | rowspan=2| | β⁻ () | B | rowspan=2|0+ | rowspan=2| |- | β⁻n () | B |-id=Beryllium-12m | style="text-indent:1em" | Be | colspan="3" style="text-indent:2em" | | | IT | Be | 0+ | |-id=Beryllium-13 | Be |4 |9 | | | n ? | Be ? | (1/2−) | |-id=Beryllium-13m | style="text-indent:1em" | Be | colspan="3" style="text-indent:2em" | | | | | (5/2+) | |-id=Beryllium-14 | rowspan=5|Be | rowspan=5|4 | rowspan=5|10 | rowspan=5| | rowspan=5| | β⁻n () | B | rowspan=5|0+ | rowspan=5| |- | β⁻ (> ) | B |- | β⁻2n () | B |- | β⁻t () | Be |- | β⁻α (< ) | Li |-id=Beryllium-14m | style="text-indent:1em" | Be | colspan="3" style="text-indent:2em" | | | | | (2+) | |-id=Beryllium-15 | Be |4 |11 | | | n | Be | (5/2+) | |-id=Beryllium-16 | Be |4 |12 | |
[] |2n |Be | 0+ | Template:Isotopes table/footer

Beryllium-7

Beryllium-7 is an isotope with a half-life of 53.3 days that is generated naturally as a cosmogenic nuclide. The rate at which the short-lived Be is transferred from the air to the ground is controlled in part by the weather. Be decay in the Sun is one of the sources of solar neutrinos, and the first type ever detected using the Homestake experiment. Presence of Be 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 Be.

File:Be7fromcosmicrays.png

The rate of delivery of Be from the air to the ground in Japan

Beryllium-8

Beryllium-8 decays into two alpha particles with an extremely short half-life of seconds, a consequence of its total ground-state energy being ~92 keV greater than that of two alpha particles. This is unusual among light N = Z nuclides and creates a bottleneck in stellar nucleosynthesis, which must be bypassed by the fusion of three alpha particles to form stable carbon-12.

Beryllium-10

File:Solar Activity Proxies.png

Plot showing variations in solar activity, including variation in ¹⁰Be concentration which varies inversely with solar activity. (Note that the beryllium scale is inverted, so increases on this scale indicate lower beryllium-10 levels).

Beryllium-10 has a half-life of , and decays by beta decay to stable boron-10 with a maximum energy of 556.2 keV. It is formed in the Earth's atmosphere mainly by cosmic ray spallation of nitrogen and oxygen. ¹⁰Be and its daughter product have been used to examine soil erosion, soil formation from regolith, the development of lateritic soils and the age of ice cores. ¹⁰Be is a significant isotope used as a proxy data measure for cosmogenic nuclides to characterize solar and extra-solar attributes of the past from terrestrial samples.

Decay chains

Most isotopes of beryllium within the proton/neutron drip lines decay via beta decay and/or a combination of beta decay and alpha decay or neutron emission. However, Be decays only via electron capture, 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 Be, which decays via alpha decay to He. This alpha decay is often considered fission, which would be able to account for its extremely short half-life.

$\begin{array}{l}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{6}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}6}\mathrm{B}\mathrm{e}⟶[5\mathrm{z}\mathrm{s}]{}^{\mathrm{4}}{}_{\mathrm{2}}\mathrm{H}\mathrm{e}+2_{\mathrm{1}}^{\mathrm{1}}\mathrm{H}\\ {}^{\mathrm{7}}{}_{\mathrm{4}}\mathrm{B}\mathrm{e}+\mathrm{e}{\phantom{A}}^{-}⟶[53.22\mathrm{d}]{}^{\mathrm{7}}{}_{\mathrm{3}}\mathrm{L}\mathrm{i}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{8}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}8}\mathrm{B}\mathrm{e}⟶[81.9\mathrm{a}\mathrm{s}]2_{\mathrm{2}}^{\mathrm{4}}\mathrm{H}\mathrm{e}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{10}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}10}\mathrm{B}\mathrm{e}⟶[1.387\mathrm{M}\mathrm{a}]{}^{\mathrm{1}\mathrm{0}}{}_{\mathrm{5}}\mathrm{B}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{11}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}11}\mathrm{B}\mathrm{e}⟶[13.76\mathrm{s}]{}^{\mathrm{1}\mathrm{1}}{}_{\mathrm{5}}\mathrm{B}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{11}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}11}\mathrm{B}\mathrm{e}⟶[13.76\mathrm{s}]{}^{\mathrm{7}}{}_{\mathrm{3}}\mathrm{L}\mathrm{i}+{}^{\mathrm{4}}{}_{\mathrm{2}}\mathrm{H}\mathrm{e}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{12}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}12}\mathrm{B}\mathrm{e}⟶[21.46\mathrm{m}\mathrm{s}]{}^{\mathrm{1}\mathrm{2}}{}_{\mathrm{5}}\mathrm{B}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{12}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}12}\mathrm{B}\mathrm{e}⟶[21.46\mathrm{m}\mathrm{s}]{}^{\mathrm{1}\mathrm{1}}{}_{\mathrm{5}}\mathrm{B}+{}^{\mathrm{1}}{}_{\mathrm{0}}\mathrm{n}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{13}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}13}\mathrm{B}\mathrm{e}⟶[1\mathrm{z}\mathrm{s}]{}^{\mathrm{1}\mathrm{2}}{}_{\mathrm{4}}\mathrm{B}\mathrm{e}+{}^{\mathrm{1}}{}_{\mathrm{0}}\mathrm{n}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{14}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}14}\mathrm{B}\mathrm{e}⟶[4.53\mathrm{m}\mathrm{s}]{}^{\mathrm{1}\mathrm{3}}{}_{\mathrm{5}}\mathrm{B}+{}^{\mathrm{1}}{}_{\mathrm{0}}\mathrm{n}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{14}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}14}\mathrm{B}\mathrm{e}⟶[4.53\mathrm{m}\mathrm{s}]{}^{\mathrm{1}\mathrm{4}}{}_{\mathrm{5}}\mathrm{B}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{14}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}14}\mathrm{B}\mathrm{e}⟶[4.53\mathrm{m}\mathrm{s}]{}^{\mathrm{1}\mathrm{2}}{}_{\mathrm{5}}\mathrm{B}+2_{\mathrm{0}}^{\mathrm{1}}\mathrm{n}+\mathrm{e}{\phantom{A}}^{-}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{15}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}15}\mathrm{B}\mathrm{e}⟶[790\mathrm{y}\mathrm{s}]{}^{\mathrm{1}\mathrm{4}}{}_{\mathrm{4}}\mathrm{B}\mathrm{e}+{}^{\mathrm{1}}{}_{\mathrm{0}}\mathrm{n}\\ {\phantom{A}}_{\phantom{4}}^{\phantom{16}}{\phantom{A}}_{\phantom{2}4}^{\phantom{2}16}\mathrm{B}\mathrm{e}⟶[650\mathrm{y}\mathrm{s}]{}^{\mathrm{1}\mathrm{4}}{}_{\mathrm{4}}\mathrm{B}\mathrm{e}+2_{\mathrm{0}}^{\mathrm{1}}\mathrm{n}\\ \end{array}$

See also

Daughter products other than beryllium

• Isotopes of boron
• Isotopes of lithium
• Isotopes of helium