Isotopes of beryllium

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.

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)
	9.0121831±0.0000005[2] 9.0122±0.0001 (abridged)[3]
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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.

List of isotopes

Nuclide [n 2]	Z	N	Isotopic mass (Da)[5] [n 3][n 4]	Half-life[1] [resonance width]	Decay mode[1] [n 5]	Daughter isotope [n 6]	Spin and parity[1] [n 7]	Isotopic abundance
	Excitation energy
6 Be[n 8]	4	2	6.019726(6)	5.0(3) zs [91.6(5.6) keV]	2p	4 He	0+
7 Be[n 9]	4	3	7.01692871(8)	53.22(6) d	ε	7 Li	3/2−	Trace[n 10]
8 Be[n 11]	4	4	8.00530510(4)	81.9(3.7) as [5.58(25) eV]	α[n 1]	4 He	0+
8m Be	16626(3) keV				α	4 He	2+
9 Be	4	5	9.01218306(8)	Stable			3/2−	1
9m Be	14390.3(1.7) keV			1.25(10) as [367(30) eV]			3/2−
10 Be	4	6	10.01353469(9)	1.387(12)×106 y[nb 1]	β−	10 B	0+	Trace[n 10]
11 Be[n 12]	4	7	11.02166108(26)	13.76(7) s	β− (96.7(1)%)	11 B	1/2+
					β−α (3.3(1)%)	7 Li
					β−p (0.0013(3)%)	10 Be
11m Be	21158(20) keV			0.93(13) zs [500(75) keV]	IT ?	11 Be	3/2−
12 Be	4	8	12.0269221(20)	21.46(5) ms	β− (99.50(3)%)	12 B	0+
					β−n (0.50(3)%)	11 B
12m Be	2251(1) keV			233(7) ns	IT	12 Be	0+
13 Be	4	9	13.036135(11)	1.0(7) zs	n ?	12 Be	(1/2−)
13m Be	1500(50) keV						(5/2+)
14 Be[n 13]	4	10	14.04289(14)	4.53(27) ms	β−n (86(6)%)	13 B	0+
					β− (> 9.0(6.3)%)	14 B
					β−2n (5(2)%)	12 B
					β−t (0.02(1)%)	11 Be
					β−α (< 0.004%)	10 Li
14m Be	1520(150) keV						(2+)
15 Be	4	11	15.05349(18)	790(270) ys	n	14 Be	(5/2+)
16 Be	4	12	16.06167(18)	650(130) ys [0.73(18) MeV]	2n	14 Be	0+
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1. Also can be considered spontaneous fission, as ⁸
   Be splits into two equal ⁴
   He nuclei
2. ^mBe – Excited nuclear isomer.
3. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
4. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
5. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   n:	Neutron emission
   p:	Proton emission

6. Bold symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. Intermediate in the proton–proton chain (final step of PP I).
9. Produced in Big Bang nucleosynthesis, but not primordial, as it all quickly decayed to ⁷Li
10. cosmogenic nuclide
11. Intermediate product of triple alpha process in stellar nucleosynthesis
12. Has 1 halo neutron
13. Has 4 halo neutrons

Beryllium-7

Beryllium-7 is an isotope with a half-life of 53.22 days that is generated naturally as a cosmogenic nuclide.^[4] The rate at which the short-lived ⁷
Be is transferred from the air to the ground is controlled in part by the weather. ⁷
Be 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 ⁷
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 ⁷
Be.^[6]

The rate of delivery of ⁷
Be from the air to the ground in Japan^[6]

Beryllium-8

Main article: 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 requireds 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

Main article: 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 has a half-life of 1.387×10⁶ y, and beta decays 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 on nitrogen and oxygen.^{[7][8][4] 10}Be 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.^{[9] 10}Be 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.^[10]

Decay chains

Isotopes of beryllium heavier than the stable ⁹Be decay via beta decay or a combination of beta decay and neutron emission. However, ⁸
Be splits in two to result in ⁴
He. Then, ⁷
Be 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).^[11] 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:

${\displaystyle {\begin{array}{l}{}\\{\ce {^{6}_{4}Be->[5\ {\ce {zs}}]{^{4}_{2}He}+{2_{1}^{1}H}}}\\{\ce {{^{7}_{4}Be}+e^{-}->[53.22\ {\ce {d}}]{^{7}_{3}Li}}}\\{\ce {^{8}_{4}Be->[81.9\ {\ce {as}}]{2_{2}^{4}He}}}\\{\ce {^{10}_{4}Be->[1.387\ {\ce {Ma}}]{^{10}_{5}B}+e^{-}}}\\{\ce {^{11}_{4}Be->[13.76\ {\ce {s}}]{^{11}_{5}B}+e^{-}}}\\{\ce {^{11}_{4}Be->[13.76\ {\ce {s}}]{^{7}_{3}Li}+{^{4}_{2}He}+e^{-}}}\\{\ce {^{12}_{4}Be->[21.46\ {\ce {ms}}]{^{12}_{5}B}+e^{-}}}\\{\ce {^{12}_{4}Be->[21.46\ {\ce {ms}}]{^{11}_{5}B}+{^{1}_{0}n}+e^{-}}}\\{\ce {^{13}_{4}Be->[1\ {\ce {zs}}]{^{12}_{4}Be}+{^{1}_{0}n}}}\\{\ce {^{14}_{4}Be->[4.53\ {\ce {ms}}]{^{13}_{5}B}+{^{1}_{0}n}+e^{-}}}\\{\ce {^{14}_{4}Be->[4.53\ {\ce {ms}}]{^{14}_{5}B}+e^{-}}}\\{\ce {^{14}_{4}Be->[4.53\ {\ce {ms}}]{^{12}_{5}B}+{2_{0}^{1}n}+e^{-}}}\\{\ce {^{15}_{4}Be->[790\ {\ce {ys}}]{^{14}_{4}Be}+{^{1}_{0}n}}}\\{}{\ce {^{16}_{4}Be->[650\ {\ce {ys}}]{^{14}_{4}Be}+{2_{0}^{1}n}}}\\{}\end{array}}}$

See also

Daughter products other than beryllium

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

Notes

1. Note that NUBASE2020 uses the tropical year to convert between years and other units of time, not the Gregorian year. The relationship between years and other time units in NUBASE2020 is as follows: 1 y = 365.2422 d = 31 556 926 s