Physics:Isotopes of beryllium

Main isotopes of Chemistry:beryllium (₄Be)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 7Be trace 53.12 d ε 7Li γ – 9Be 100% stable 10Be trace 1.39×106 y β− 10B
Standard atomic weight Ar, standard(Be)	9.0121831(5)

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 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; 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 with a half-life of 1.387 million years and with a half-life of 53.22 days. All other radioisotopes have half-lives shorter than 15 seconds.

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 toward splitting into two 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 and are both cosmogenic nuclides because they are made, in the Solar System, continually at the rate they decay by spallation, as is carbon-14.

List of isotopes

Template:Isotope table discovery |-id=Beryllium-6 | | 4 | 2 | 6.019726(6) | style="text-align:center" | 1958 | 5.0(3) zs
[91.6(5.6) keV] | 2p | | 0+ | |- | | 4 | 3 | 7.01692871(8) | style="text-align:center" | 1938 | 53.22(6) d | ε | | 3/2− | Trace |- | [[Beryllium-8|]] | 4 | 4 | 8.00530510(4) | style="text-align:center" | 1932 | 81.9(3.7) as
[5.58(25) eV] | α | | 0+ | |-id=Beryllium-9 | | 4 | 5 | 9.01218306(8) | style="text-align:center" | 1921 | colspan=3 align=center|Stable | 3/2− | 1 |-id=Beryllium-10 | | 4 | 6 | 10.01353469(9) | style="text-align:center" | 1935 | 1.387(12)×10⁶ y | β⁻ | | 0+ | Trace |-id=Beryllium-11 | rowspan=3| | rowspan=3|4 | rowspan=3|7 | rowspan=3|11.02166108(26) | rowspan=3 style="text-align:center" | 1958 | rowspan=3|13.76(7) s | β⁻ (96.7(1)%) | | rowspan=3|1/2+ | rowspan=3| |- | β⁻α (3.3(1)%) | |- | β⁻p (0.0013(3)%) | |-id=Beryllium-12 | rowspan=2| | rowspan=2|4 | rowspan=2|8 | rowspan=2|12.0269221(20) | rowspan=2 style="text-align:center" | 1966

| rowspan=2|21.46(5) ms | β⁻ (99.50(3)%) | | rowspan=2|0+ | rowspan=2| |- | β⁻n (0.50(3)%) | |-id=Beryllium-12m | style="text-indent:1em" | | colspan="3" style="text-indent:2em" | 2251(1) keV | style="text-align:center" | 2003 | 233(7) ns | IT | | 0+ | |-id=Beryllium-13 | | 4 | 9 | 13.036135(11) | style="text-align:center" | 1983 | 1.0(7) zs | n ? | | (1/2−) | |-id=Beryllium-14 | rowspan=5| | rowspan=5|4 | rowspan=5|10 | rowspan=5|14.04289(14) | rowspan=5 style="text-align:center" | 1973

| rowspan=5|4.53(27) ms | β⁻n (86(6)%) | | rowspan=5|0+ | rowspan=5| |- | β⁻ (> 9.0(6.3)%) | |- | β⁻2n (5(2)%) | |- | β⁻t (0.02(1)%) | |- | β⁻α (< 0.004%) | |-id=Beryllium-15 | | 4 | 11 | 15.05349(18) | style="text-align:center" | 2013 | 790(270) ys | n | | (5/2+) | |-id=Beryllium-16 | | 4 | 12 | 16.06167(18) | style="text-align:center" | 2012 | 650(130) ys
[0.73(18) MeV] | 2n | | 0+ | |}

Beryllium-7

Beryllium-7 is an isotope with a half-life of 53.22 days that is generated naturally as a cosmogenic nuclide. It is also a nuisance byproduct in nuclear reactors and accelerators. 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 (the half-life in stars can be greatly different from the normal as it is a free rather than a bound electron that is captured) 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 .

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

Beryllium-8

Main article: Physics:Beryllium-8

Beryllium-8 decays immediately into two alpha particles as its total energy is about 92 keV greater than that of the two alpha particles, and the Coulomb barrier to decay is negligible. This is unusual among light N = Z nuclides and creates a bottleneck in stellar nucleosynthesis, which requires that a third alpha be immediately captured, known as the fusion of three alpha particles, to form stable carbon-12 and thence all heavier elements.

Beryllium-10

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 (¹⁰Be) has a half-life of 1.387 million years and beta decays to stable Boron-10 with a maximum energy of 556.0 keV:

¹⁰Be → ¹⁰B + e⁻.

Beryllium-10 is formed in the Earth's atmosphere mainly by cosmic ray spallation of nitrogen and oxygen.

Because beryllium tends to exist in solutions below about pH 5.5 (and rainwater above many industrialized areas can have a pH less than 5), it will dissolve and be transported to the Earth's surface via rainwater. As the precipitation quickly becomes more alkaline, beryllium drops out of solution. Cosmogenic ¹⁰Be thereby accumulates at the soil surface, where its relatively long half-life does not limit its residence time there.

¹⁰Be and its daughter product have been used in surface exposure dating to examine soil erosion, soil formation from regolith, the development of lateritic soils and the age of ice cores. It is also formed in nuclear explosions by a reaction of fast neutrons with ¹³C in the carbon dioxide in air, and is one of the historical indicators of past activity at nuclear test sites. ¹⁰Be decay 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.

The rate of production of beryllium-10 depends on the activity of the sun. When solar activity is low (low numbers of sunspots and low solar wind), the barrier against cosmic rays that exists beyond the termination shock is weakened (see Cosmic ray). This means more beryllium-10 is produced, and it can be detected millennia later. Beryllium-10 can thus serve as a marker of Miyake events, such as the 774–775 carbon-14 spike. There can be an effect on climate (see Homeric Minimum). While other cosmogenic isotopes experience similar cycles, the high rate of production, long half-life, and relative immobility in the environment make this most suitable for this purpose.

Decay chains

Isotopes of beryllium heavier than the stable ⁹Be decay via beta decay or a combination of beta decay and neutron emission. However, splits in two to result in . Then, decays only via electron capture, an exceptional occurrence in such a light element. For this reason, its half-life can be artificially lowered by 0.83% via endohedral enclosure (⁷Be@C₆₀). Finally even lighter isotopes decay exclusively by emitting protons and are also (like ⁸Be) unbound. The decay of all known beryllium isotopes is summarized as follows:

$\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