Beryllium-8: Difference between revisions

Beryllium-8, ⁸Be
General
Symbol	8Be
Names	beryllium-8, 8Be, Be-8
Protons (Z)	4
Neutrons (N)	4
Nuclide data
Natural abundance	0 (extinct)
Half-life (t1/2)	(8.19±0.37)×10−17 s
Isotope mass	8.00530510(4) Da
Spin	0
Decay products	4He
Decay modes
Decay mode	Decay energy (MeV)
α	(91.84±4)×10−3
	Isotopes of beryllium ; Complete table of nuclides

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Beryllium-8 (⁸Be, Be-8) is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium. It decays into two alpha particles with a half-life on the order of 8.19×10⁻¹⁷ seconds. This has important ramifications in stellar nucleosynthesis as it creates a bottleneck in the creation of heavier chemical elements. The properties of ⁸Be have also led to speculation on the fine tuning of the Universe, and theoretical investigations on cosmological evolution had ⁸Be been stable.

Discovery

The discovery of beryllium-8 occurred shortly after the construction of the first particle accelerator in 1932. Physicists John Douglas Cockcroft and Ernest Walton performed their first experiment with their accelerator at the Cavendish Laboratory in Cambridge, in which they irradiated lithium-7 with protons. They reported that this populated a nucleus with A = 8 that near-instantaneously decays into two alpha particles. This activity was observed again several months later, and was inferred to originate from ⁸Be.^[3]

Properties

Beryllium-8 is unbound with respect to alpha emission by 92 keV; it is a resonance having a width of 6 eV.^[4] The nucleus of helium-4 is particularly stable, having a doubly magic configuration and larger binding energy per nucleon than ⁸Be. As the total energy of ⁸Be is greater than that of two alpha particles, the decay into two alpha particles is energetically favorable,^[5] and the synthesis of ⁸Be from two ⁴He nuclei is endothermic. The decay of ⁸Be is facilitated by the structure of the ⁸Be nucleus; it is highly deformed, and is believed to be a molecule-like cluster of two alpha particles that are very easily separated.^[6]^[7] Furthermore, while other alpha nuclides have similar short-lived resonances, ⁸Be is exceptionally already in the ground state. The unbound system of two α-particles has a low energy of the Coulomb barrier, which enables its existence for any significant length of time.^[8] Namely, ⁸Be decays with a half-life of 8.19×10⁻¹⁷ seconds.^[9]

Beryllium-8 is the only unstable nuclide with the same even number ≤ 20 of protons and neutrons. It is also one of the only two unstable nuclides (the other is helium-5) with mass number ≤ 143 which are stable to both beta decay and double beta decay.

There are also several excited states of ⁸Be, all short-lived resonances – having widths up to several MeV and varying isospins – that quickly decay to the ground state or into two alpha particles.^[10]

Decay anomaly and possible fifth force

A 2015 experiment by Attila Krasznahorkay et al. at the Hungarian Academy of Sciences's Institute for Nuclear Research found anomalous decays in the 17.64 and 18.15 MeV excited states of ⁸Be, populated by proton irradiation of ⁷Li. An excess of decays creating electron-positron pairs at a 140° angle with a combined energy of 17 MeV was observed. Jonathan Feng et al. attribute this 6.8-σ anomaly to a 17 MeV protophobic X-boson dubbed the X17 particle. This boson would mediate a fifth fundamental force acting over a short range (12 fm) and perhaps explain the decay of these ⁸Be excited states.^[10] A 2018 rerun of this experiment found the same anomalous particle scattering and set a narrower mass range of the proposed fifth boson, 17.01±0.16 MeV/c².^[11] While further experiments are needed to corroborate these observations, the influence of a fifth boson has been proposed as "the most straightforward possibility".^[12]

Role in stellar nucleosynthesis

In stellar nucleosynthesis, two helium-4 nuclei may collide and fuse into a single beryllium-8 nucleus. Beryllium-8 has an extremely short half-life (8.19×10⁻¹⁷ seconds), and decays back into two helium-4 nuclei. This, along with the unbound nature of ⁵He and ⁵Li, creates a bottleneck in Big Bang nucleosynthesis and stellar nucleosynthesis,^[8] for it necessitates a very fast reaction rate.^[13] This impedes formation of heavier elements in the former, and limits the yield in the latter process. If the beryllium-8 collides with a helium-4 nucleus before decaying, they can fuse into a carbon-12 nucleus. This reaction was first theorized independently by Öpik^[14] and Salpeter^[15] in the early 1950s.

Owing to the instability of ⁸Be, the triple-alpha process is the only reaction in which ¹²C and heavier elements may be produced in observed quantities. The triple-alpha process, despite being a three-body reaction, is facilitated when ⁸Be production increases such that its concentration is approximately 10⁻⁸ relative to ⁴He;^[16] this occurs when ⁸Be is produced faster than it decays.^[17] However, this alone is insufficient, as the collision between ⁸Be and ⁴He is more likely to break apart the system rather than enable fusion;^[18] the reaction rate would still not be fast enough to explain the observed abundance of ¹²C.^[1] In 1954, Fred Hoyle thus postulated the existence of a resonance in carbon-12 within the stellar energy region of the triple-alpha process, enhancing the creation of carbon-12 despite the extremely short half-life of beryllium-8.^[19] The existence of this resonance (the Hoyle state) was confirmed experimentally shortly thereafter; its discovery has been cited in formulations of the anthropic principle and the fine-tuned Universe hypothesis.^[20]^[21]

Hypothetical universes with stable ⁸Be

As beryllium-8 is unbound by only 92 keV, it is theorized that very small changes in nuclear potential and the fine tuning of certain constants (such as α, the fine structure constant), could sufficiently increase the binding energy of ⁸Be to prevent its alpha decay, thus making it stable. This has led to investigations of hypothetical scenarios in which ⁸Be is stable and speculation about other universes with different fundamental constants.^[1] These studies suggest that the disappearance of the bottleneck^[20] created by ⁸Be would result in a very different reaction mechanism in Big Bang nucleosynthesis and the triple-alpha process, as well as alter the abundances of heavier chemical elements.^[4] As Big Bang nucleosynthesis only occurred within a short period having the necessary conditions, it is thought that there would be no significant difference in carbon production even if ⁸Be were stable.^[8] However, stable ⁸Be would enable alternative reaction pathways in helium burning (such as ⁸Be + ⁴He and ⁸Be + ⁸Be; constituting a "beryllium burning" phase) and possibly affect the abundance of the resultant ¹²C, ¹⁶O, and heavier nuclei, though ¹H and ⁴He would remain the most abundant nuclides. This would also affect stellar evolution through an earlier onset and faster rate of helium burning (and beryllium burning), and result in a different main sequence than our Universe.^[1]

Notes

^ ⁸Be does not occur naturally on Earth, but it exists in secular equilibrium in the cores of helium-burning stars.^[1]

References

^ ^a ^b ^c ^d Adams, F. C.; Grohs, E. (2017). "Stellar helium burning in other universes: A solution to the triple alpha fine-tuning problem". Astroparticle Physics. 7: 40–54. arXiv:1608.04690. Bibcode:2017APh....87...40A. doi:10.1016/j.astropartphys.2016.12.002. S2CID 119287629.
^ Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF). Chinese Physics C. 41 (3): 030003-1–030003-442. doi:10.1088/1674-1137/41/3/030003.
^ Thoennessen, M. (2016). The Discovery of Isotopes: A Complete Compilation. Springer. pp. 45–48. doi:10.1007/978-3-319-31763-2. ISBN 978-3-319-31761-8. LCCN 2016935977.
^ ^a ^b Coc, A.; Olive, K. A.; Uzan, J.-P.; Vangioni, E. (2012). "Variation of fundamental constants and the role of A = 5 and A = 8 nuclei on primordial nucleosynthesis". Physical Review D. 86 (4): 043529. arXiv:1206.1139. Bibcode:2012PhRvD..86d3529C. doi:10.1103/PhysRevD.86.043529. S2CID 119230483.
^ Schatz, H.; Blaum, K. (2006). "Nuclear masses and the origin of the elements" (PDF). Europhysics News. 37 (5): 16–21. Bibcode:2006ENews..37e..16S. doi:10.1051/epn:2006502.
^ Freer, M. (2014). "Clustering in Light Nuclei; from the Stable to the Exotic" (PDF). In Scheidenberger, C.; Pfützner, M. (eds.). The Euroschool on Exotic Beams: Lecture Notes in Physics. Lecture Notes in Physics. Vol. 4. Springer. pp. 1–37. doi:10.1007/978-3-642-45141-6. ISBN 978-3-642-45140-9. ISSN 0075-8450.
^ Zhou, B.; Ren, Z. (2017). "Nonlocalized clustering in nuclei". Advances in Physics. 2 (2): 359–372. Bibcode:2017AdPhX...2..359Z. doi:10.1080/23746149.2017.1294033.
^ ^a ^b ^c Coc, A.; Vangioni, E. (2014). "The triple-alpha reaction and the A = 8 gap in BBN and Population III stars" (PDF). Memorie della Società Astronomica Italiana. 85: 124–129. Bibcode:2014MmSAI..85..124C.
^ Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
^ ^a ^b Feng, J. L.; Fornal, B.; Galon, I.; et al. (2016). "Evidence for a protophobic fifth force from ⁸Be nuclear transitions". Physical Review Letters. 117 (7): 071803. arXiv:1604.07411. doi:10.1103/PhysRevLett.117.071803. PMID 27563952. S2CID 206279817.
^ Krasznahorkay, A. J.; Csatlós, M.; Csige, L.; et al. (2018). "New results on the ⁸Be anomaly" (PDF). Journal of Physics: Conference Series. 1056 (1): 012028. Bibcode:2018JPhCS1056a2028K. doi:10.1088/1742-6596/1056/1/012028.
^ Cartlidge, E. (25 May 2016). "Has a Hungarian physics lab found a fifth force of nature?". Nature. Retrieved 14 July 2019.
^ Landsman, K. (2015). "The Fine-Tuning Argument". arXiv:1505.05359 [physics.hist-ph].
^ Öpik, E. J. (1951). "Stellar Models with Variable Composition. II. Sequences of Models with Energy Generation Proportional to the Fifteenth Power of Temperature". Proceedings of the Royal Irish Academy, Section A. 54: 49–77. JSTOR 20488524.
^ Salpeter, E. E. (1952). "Nuclear Reactions in the Stars. I. Proton-Proton Chain"". Physical Review. 88 (3): 547–553. Bibcode:1952PhRv...88..547S. doi:10.1103/PhysRev.88.547.
^ Piekarewicz, J. (2014). "The Birth, Life, and Death of Stars" (PDF). Florida State University. Retrieved 13 July 2019.
^ Sadeghi, H.; Pourimani, R.; Moghadasi, A. (2014). "Two-helium radiative capture process and the ⁸Be nucleus at settler energies". Astrophysics and Space Science. 350 (2): 707–712. Bibcode:2014Ap&SS.350..707S. doi:10.1007/s10509-014-1806-1. S2CID 123444620.
^ Inglis-Arkell, E. "This Unbelievable Coincidence Is Responsible For Life In The Universe". Gizmodo. Retrieved 14 July 2019.
^ Hoyle, F. (1954). "On Nuclear Reactions Occurring in Very Hot STARS. I. the Synthesis of Elements from Carbon to Nickel". Astrophysical Journal Supplement. 1: 121–146, doi:10.1086/190005
^ ^a ^b Epelbaum, E.; Krebs, H.; Lee, D.; Meißner, Ulf-G. (2011). "Ab initio calculation of the Hoyle state". Physical Review Letters. 106 (19): 192501–1–192501–4. arXiv:1101.2547. Bibcode:2011PhRvL.106s2501E. doi:10.1103/PhysRevLett.106.192501. PMID 21668146. S2CID 33827991.
^ Jenkins, David; Kirsebom, Oliver (2013-02-07). "The secret of life". Physics World. Archived from the original on 2021-02-13. Retrieved 2021-08-21.

Lighter: beryllium-7	Beryllium-8 is an isotope of beryllium	Heavier: beryllium-9
Decay product of: carbon-9 (β⁺, p) boron-9 (p) lithium-8 (β⁻)	Decay chain of beryllium-8	Decays to: helium-4 (α)

[2] ⁸Be does not occur naturally on Earth, but it exists in secular equilibrium in the cores of helium-burning stars.^[1]

[otheru-1] Adams, F. C.; Grohs, E. (2017). "Stellar helium burning in other universes: A solution to the triple alpha fine-tuning problem". Astroparticle Physics. 7: 40–54. arXiv:1608.04690. Bibcode:2017APh....87...40A. doi:10.1016/j.astropartphys.2016.12.002. S2CID 119287629.

[AME2016_II-3] Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF). Chinese Physics C. 41 (3): 030003-1–030003-442. doi:10.1088/1674-1137/41/3/030003.

[isodisc-4] Thoennessen, M. (2016). The Discovery of Isotopes: A Complete Compilation. Springer. pp. 45–48. doi:10.1007/978-3-319-31763-2. ISBN 978-3-319-31761-8. LCCN 2016935977.

[a58-5] Coc, A.; Olive, K. A.; Uzan, J.-P.; Vangioni, E. (2012). "Variation of fundamental constants and the role of A = 5 and A = 8 nuclei on primordial nucleosynthesis". Physical Review D. 86 (4): 043529. arXiv:1206.1139. Bibcode:2012PhRvD..86d3529C. doi:10.1103/PhysRevD.86.043529. S2CID 119230483.

[schatz-6] Schatz, H.; Blaum, K. (2006). "Nuclear masses and the origin of the elements" (PDF). Europhysics News. 37 (5): 16–21. Bibcode:2006ENews..37e..16S. doi:10.1051/epn:2006502.

[exb1-7] Freer, M. (2014). "Clustering in Light Nuclei; from the Stable to the Exotic" (PDF). In Scheidenberger, C.; Pfützner, M. (eds.). The Euroschool on Exotic Beams: Lecture Notes in Physics. Lecture Notes in Physics. Vol. 4. Springer. pp. 1–37. doi:10.1007/978-3-642-45141-6. ISBN 978-3-642-45140-9. ISSN 0075-8450.

[cluster-8] Zhou, B.; Ren, Z. (2017). "Nonlocalized clustering in nuclei". Advances in Physics. 2 (2): 359–372. Bibcode:2017AdPhX...2..359Z. doi:10.1080/23746149.2017.1294033.

[8gap-9] Coc, A.; Vangioni, E. (2014). "The triple-alpha reaction and the A = 8 gap in BBN and Population III stars" (PDF). Memorie della Società Astronomica Italiana. 85: 124–129. Bibcode:2014MmSAI..85..124C.

[NUBASE2016-10] Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.

[5force-11] Feng, J. L.; Fornal, B.; Galon, I.; et al. (2016). "Evidence for a protophobic fifth force from ⁸Be nuclear transitions". Physical Review Letters. 117 (7): 071803. arXiv:1604.07411. doi:10.1103/PhysRevLett.117.071803. PMID 27563952. S2CID 206279817.

[expt18-12] Krasznahorkay, A. J.; Csatlós, M.; Csige, L.; et al. (2018). "New results on the ⁸Be anomaly" (PDF). Journal of Physics: Conference Series. 1056 (1): 012028. Bibcode:2018JPhCS1056a2028K. doi:10.1088/1742-6596/1056/1/012028.

[5fnews-13] Cartlidge, E. (25 May 2016). "Has a Hungarian physics lab found a fifth force of nature?". Nature. Retrieved 14 July 2019.

[exft-14] Landsman, K. (2015). "The Fine-Tuning Argument". arXiv:1505.05359 [physics.hist-ph].

[15] Öpik, E. J. (1951). "Stellar Models with Variable Composition. II. Sequences of Models with Energy Generation Proportional to the Fifteenth Power of Temperature". Proceedings of the Royal Irish Academy, Section A. 54: 49–77. JSTOR 20488524.

[16] Salpeter, E. E. (1952). "Nuclear Reactions in the Stars. I. Proton-Proton Chain"". Physical Review. 88 (3): 547–553. Bibcode:1952PhRv...88..547S. doi:10.1103/PhysRev.88.547.

[bld-17] Piekarewicz, J. (2014). "The Birth, Life, and Death of Stars" (PDF). Florida State University. Retrieved 13 July 2019.

[rcap-18] Sadeghi, H.; Pourimani, R.; Moghadasi, A. (2014). "Two-helium radiative capture process and the ⁸Be nucleus at settler energies". Astrophysics and Space Science. 350 (2): 707–712. Bibcode:2014Ap&SS.350..707S. doi:10.1007/s10509-014-1806-1. S2CID 123444620.

[gizmodo-19] Inglis-Arkell, E. "This Unbelievable Coincidence Is Responsible For Life In The Universe". Gizmodo. Retrieved 14 July 2019.

[20] Hoyle, F. (1954). "On Nuclear Reactions Occurring in Very Hot STARS. I. the Synthesis of Elements from Carbon to Nickel". Astrophysical Journal Supplement. 1: 121–146, doi:10.1086/190005

[hoyles-21] Epelbaum, E.; Krebs, H.; Lee, D.; Meißner, Ulf-G. (2011). "Ab initio calculation of the Hoyle state". Physical Review Letters. 106 (19): 192501–1–192501–4. arXiv:1101.2547. Bibcode:2011PhRvL.106s2501E. doi:10.1103/PhysRevLett.106.192501. PMID 21668146. S2CID 33827991.

[22] Jenkins, David; Kirsebom, Oliver (2013-02-07). "The secret of life". Physics World. Archived from the original on 2021-02-13. Retrieved 2021-08-21.

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@@ Line 1: / Line 1: @@
 {{Short description|Isotope of beryllium}}
 {{Infobox isotope
-    | image =
+ | image =
-    | alternate_names =
+ | alternate_names =
-    | mass_number = 8
+ | mass_number = 8
-    | symbol = Be
+ | symbol = Be
-    | num_neutrons = 4
+ | num_neutrons = 4
-    | num_protons = 4
+ | num_protons = 4
-    | abundance = 0 (extinct){{efn|It does not occur naturally on Earth, but it exists in [[secular equilibrium]] in the cores of helium-burning stars.<ref name=otheru/>}}
+ | abundance = 0 (extinct){{efn|<sup>8</sup>Be does not occur naturally on Earth, but it exists in [[secular equilibrium]] in the cores of helium-burning stars.<ref name=otheru/>}}
-    | halflife = 8.19(37)×10<sup>−17</sup> s
+ | halflife = {{val|8.19|0.37|e=−17 |u=s}}
+ | decay_product =
-    | error_halflife =
+ | decay_mass =4
-    | decay_product =
+ | decay_symbol =He
-    | decay_mass =4
+ | mass = 8.00530510(4)
-    | decay_symbol =He
+ | spin =0
-    | mass = 8.00530510(4)
+ | excess_energy =
-    | spin =0
+ | binding_energy =
-    | excess_energy =
+ | decay_mode1 =[[Alpha decay|α]]
-    | error1 =
+ | decay_energy1 ={{val|91.84|4|e=-3}}{{AME2016 II|ref}}
-    | binding_energy =
-    | error2 =
+ | decay_mode2 =
+ | decay_energy2 =
-    | decay_mode1 =[[Alpha decay|α]]
+ | decay_mode3 =
-    | decay_energy1 ={{val|91.84|4|e=-3}}{{AME2016 II|ref}}
+ | decay_energy3 =
-    | decay_mode2 =
+ | decay_mode4 =
-    | decay_energy2 =
+ | decay_energy4 =
-    | decay_mode3 =
-    | decay_energy3 =
-    | decay_mode4 =
-    | decay_energy4 =
     }}
-'''Beryllium-8''' ('''<sup>8</sup>Be''', '''Be-8''') is a [[radionuclide]] with 4 [[neutron]]s and 4 [[proton]]s. It is an unbound [[resonance (particle physics)|resonance]] and nominally an [[isotopes of beryllium|isotope of beryllium]]. It decays into two alpha particles with a half-life on the order of 8.19{{e|−17}}&nbsp;seconds. This has important ramifications in [[stellar nucleosynthesis]] as it creates a bottleneck in the creation of heavier [[chemical element]]s. The properties of <sup>8</sup>Be have also led to speculation on the [[fine-tuned universe|fine tuning]] of the [[Universe]], and theoretical investigations on cosmological evolution had <sup>8</sup>Be been stable.
+'''Beryllium-8''' ('''<sup>8</sup>Be''', '''Be-8''') is a [[radionuclide]] with 4 [[neutron]]s and 4 [[proton]]s. It is an unbound [[resonance (particle physics)|resonance]] and nominally an [[isotopes of beryllium|isotope of beryllium]]. It decays into two [[alpha particle]]s with a half-life on the order of 8.19{{e|−17}}&nbsp;seconds. This has important ramifications in [[stellar nucleosynthesis]] as it creates a bottleneck in the creation of heavier [[chemical element]]s. The properties of <sup>8</sup>Be have also led to speculation on the [[fine-tuned universe|fine tuning]] of the [[Universe]], and theoretical investigations on cosmological evolution had <sup>8</sup>Be been stable.
 == Discovery ==
-The discovery of beryllium-8 occurred shortly after the construction of the first [[particle accelerator]] in 1932. British physicists [[John Douglas Cockcroft]] and [[Ernest Walton]] performed their first experiment with their accelerator at the [[Cavendish Laboratory]] in [[Cambridge, England|Cambridge]], in which they irradiated [[lithium-7]] with [[proton]]s. They reported that this populated a nucleus with ''A''&nbsp;=&nbsp;8 that near-instantaneously decays into two alpha particles. This activity was observed again several months later, and was inferred to originate from <sup>8</sup>Be.<ref name=isodisc>{{Thoennessen2016|pages=45–48}}</ref>
+The discovery of beryllium-8 occurred shortly after the construction of the first [[particle accelerator]] in 1932. Physicists [[John Douglas Cockcroft]] and [[Ernest Walton]] performed their first experiment with their accelerator at the [[Cavendish Laboratory]] in [[Cambridge, England|Cambridge]], in which they irradiated [[lithium-7]] with [[proton]]s. They reported that this populated a nucleus with ''A''&nbsp;=&nbsp;8 that near-instantaneously decays into two alpha particles. This activity was observed again several months later, and was inferred to originate from <sup>8</sup>Be.<ref name=isodisc>{{Thoennessen2016|pages=45–48}}</ref>
 == Properties ==
 [[File:Triple-Alpha Process.svg|left|thumb|300px|Triple-alpha process]]
-Beryllium-8 is [[nuclear drip line|unbound]] with respect to alpha emission by 92 keV; it is a resonance having a width of 6 eV.<ref name=a58>{{cite journal |last1=Coc |first1=A. |last2=Olive |first2=K. A. |last3=Uzan |first3=J.-P. |last4=Vangioni |first4=E. |title=Variation of fundamental constants and the role of ''A'' = 5 and ''A'' = 8 nuclei on primordial nucleosynthesis |date=2012 |journal=Physical Review D |volume=86 |issue=4 |pages=043529 |doi=10.1103/PhysRevD.86.043529 |arxiv=1206.1139}}</ref> The nucleus of helium-4 is particularly stable, having a [[doubly magic]] configuration and larger [[nuclear binding energy|binding energy per nucleon]] than <sup>8</sup>Be. As the total energy of <sup>8</sup>Be is greater than that of two [[alpha particle]]s, the decay into two alpha particles is energetically favorable,<ref name=schatz>{{cite journal |last1=Schatz |first1=H. |last2=Blaum |first2=K. |title=Nuclear masses and the origin of the elements |date=2006 |journal=Europhysics News |volume=37 |issue=5 |pages=16–21 |doi=10.1051/epn:2006502 |url=https://www.europhysicsnews.org/articles/epn/pdf/2006/05/epn06502.pdf |doi-access=free }}</ref> and the synthesis of <sup>8</sup>Be from two <sup>4</sup>He nuclei is endothermic. The decay of <sup>8</sup>Be is facilitated by the structure of the <sup>8</sup>Be nucleus; it is highly deformed, and is believed to be a molecule-like cluster of two alpha particles that are very easily separated.<ref name=exb1>{{cite book |last=Freer |first=M. |editor-last=Scheidenberger |editor-first=C. |editor-last2=Pfützner |editor-first2=M. |title=The Euroschool on Exotic Beams: Lecture Notes in Physics |chapter=Clustering in Light Nuclei; from the Stable to the Exotic |volume=4 |pages=1–37 |publisher=Springer |date=2014 |issn=0075-8450 |isbn=978-3-642-45140-9 |doi=10.1007/978-3-642-45141-6 |chapter-url=https://www.euroschoolonexoticbeams.be/site/files/nlp/LNP879_Chapter1.pdf|series=Lecture Notes in Physics |url=http://cds.cern.ch/record/1969486 }}</ref><ref name=cluster>{{cite journal |last1=Zhou |first1=B. |last2=Ren |first2=Z. |title=Nonlocalized clustering in nuclei |date=2017 |journal=Advances in Physics |volume=2 |issue=2 |pages=359–372 |doi=10.1080/23746149.2017.1294033 |doi-access=free }}</ref> Furthermore, while other [[alpha nuclide]]s have similar short-lived resonances, <sup>8</sup>Be is exceptionally already in the [[ground state]]. The unbound system of two α-particles has a low energy of the [[Coulomb barrier]], which enables its existence for any significant length of time.<ref name=8gap/> Namely, <sup>8</sup>Be decays with a half-life of 8.19{{e|−17}}&nbsp;seconds.{{NUBASE2016|ref}}
+Beryllium-8 is [[nuclear drip line|unbound]] with respect to alpha emission by 92&nbsp;keV; it is a resonance having a width of 6&nbsp;eV.<ref name=a58>{{cite journal |last1=Coc |first1=A. |last2=Olive |first2=K. A. |last3=Uzan |first3=J.-P. |last4=Vangioni |first4=E. |title=Variation of fundamental constants and the role of ''A''&nbsp;=&nbsp;5 and ''A''&nbsp;=&nbsp;8 nuclei on primordial nucleosynthesis |date=2012 |journal=Physical Review D |volume=86 |issue=4 |pages=043529 |doi=10.1103/PhysRevD.86.043529 |arxiv=1206.1139|bibcode=2012PhRvD..86d3529C |s2cid=119230483 }}</ref> The nucleus of helium-4 is particularly stable, having a [[doubly magic]] configuration and larger [[nuclear binding energy|binding energy per nucleon]] than <sup>8</sup>Be. As the total energy of <sup>8</sup>Be is greater than that of two [[alpha particle]]s, the decay into two alpha particles is energetically favorable,<ref name=schatz>{{cite journal |last1=Schatz |first1=H. |last2=Blaum |first2=K. |title=Nuclear masses and the origin of the elements |date=2006 |journal=Europhysics News |volume=37 |issue=5 |pages=16–21 |doi=10.1051/epn:2006502 |bibcode=2006ENews..37e..16S |url=https://www.europhysicsnews.org/articles/epn/pdf/2006/05/epn06502.pdf |doi-access=free }}</ref> and the synthesis of <sup>8</sup>Be from two <sup>4</sup>He nuclei is endothermic. The decay of <sup>8</sup>Be is facilitated by the structure of the <sup>8</sup>Be nucleus; it is highly deformed, and is believed to be a molecule-like cluster of two alpha particles that are very easily separated.<ref name=exb1>{{cite book |last=Freer |first=M. |editor-last=Scheidenberger |editor-first=C. |editor-last2=Pfützner |editor-first2=M. |title=The Euroschool on Exotic Beams: Lecture Notes in Physics |chapter=Clustering in Light Nuclei; from the Stable to the Exotic |volume=4 |pages=1–37 |publisher=Springer |date=2014 |issn=0075-8450 |isbn=978-3-642-45140-9 |doi=10.1007/978-3-642-45141-6 |chapter-url=https://www.euroschoolonexoticbeams.be/site/files/nlp/LNP879_Chapter1.pdf|series=Lecture Notes in Physics |url=https://cds.cern.ch/record/1969486 }}</ref><ref name=cluster>{{cite journal |last1=Zhou |first1=B. |last2=Ren |first2=Z. |title=Nonlocalized clustering in nuclei |date=2017 |journal=Advances in Physics |volume=2 |issue=2 |pages=359–372 |doi=10.1080/23746149.2017.1294033 |bibcode=2017AdPhX...2..359Z |doi-access=free }}</ref> Furthermore, while other [[alpha nuclide]]s have similar short-lived resonances, <sup>8</sup>Be is exceptionally already in the [[ground state]]. The unbound system of two α-particles has a low energy of the [[Coulomb barrier]], which enables its existence for any significant length of time.<ref name=8gap/> Namely, <sup>8</sup>Be decays with a half-life of 8.19{{e|−17}}&nbsp;seconds.{{NUBASE2016|ref}}
+Beryllium-8 is the only unstable nuclide with the same [[even number]] ≤&nbsp;20 of [[proton]]s and [[neutron]]s. It is also one of the only two unstable nuclides (the other is [[helium-5]]) with [[mass number]] ≤&nbsp;143 which are [[Beta-decay stable isobars|stable]] to both [[beta decay]] and [[double beta decay]].
-<sup>8</sup>Be also has several excited states. These are also short-lived resonances, having widths up to several MeV and varying [[nuclear spin|isospins]], that quickly decay to the ground state or into two alpha particles.<ref name=5force>{{cite journal |last1=Feng |first1=J. L. |last2=Fornal |first2=B. |last3=Galon |first3=I. |last4=Gardner |first4=S. |last5=Smolinsky |first5=J. |last6=Tait |first6=T. M. P. |last7=Tanedo |first7=P. |display-authors=3 |date=2016 |title=Evidence for a protophobic fifth force from <sup>8</sup>Be nuclear transitions |journal=Physical Review Letters |volume=117 |issue=7 |pages=071803 |doi=10.1103/PhysRevLett.117.071803 |pmid=27563952 |arxiv=1604.07411}}</ref>
+There are also several excited states of <sup>8</sup>Be, all short-lived resonances – having widths up to several MeV and varying [[nuclear spin|isospins]] – that quickly decay to the ground state or into two alpha particles.<ref name=5force>{{cite journal |last1=Feng |first1=J. L. |last2=Fornal |first2=B. |last3=Galon |first3=I. |last4=Gardner |first4=S. |last5=Smolinsky |first5=J. |last6=Tait |first6=T. M. P. |last7=Tanedo |first7=P. |display-authors=3 |date=2016 |title=Evidence for a protophobic fifth force from <sup>8</sup>Be nuclear transitions |journal=Physical Review Letters |volume=117 |issue=7 |pages=071803 |doi=10.1103/PhysRevLett.117.071803 |pmid=27563952 |arxiv=1604.07411|s2cid=206279817 }}</ref>
 {{clear}}
 === Decay anomaly and possible fifth force ===
 {{main|X17 particle}}
-A 2015 experiment by [[Attila Krasznahorkay]] ''et al.'' at the [[ATOMKI|Hungarian Academy of Sciences's Institute for Nuclear Research]] found anomalous decays in the 17.64 and 18.15&nbsp;MeV excited states of <sup>8</sup>Be, populated by proton irradiation of <sup>7</sup>Li. An excess of decays creating [[electron]]-[[positron]] pairs at a 140° angle with a combined energy of 17&nbsp;MeV was observed. Jonathan Feng ''et al.'' attribute this 6.8-[[standard deviation|σ]] anomaly to a 17&nbsp;MeV protophobic X-[[gauge boson|boson]] dubbed the [[X17 particle]]. This boson would mediate a [[fifth force|fifth fundamental force]] acting over a short range (12&nbsp;[[femtometer|fm]]) and perhaps explain the decay of these <sup>8</sup>Be excited states.<ref name=5force/> A 2018 rerun of this experiment found the same anomalous particle scattering, and set a narrower mass range of the proposed fifth boson, {{val|17.01|0.16}} [[Electronvolt (mass)|MeV/c<sup>2</sup>]].<ref name=expt18>{{cite journal |last1=Krasznahorkay |first1=A. J. |last2=Csatlós |first2=M. |last3=Csige |first3=L. |last4=Gácsi |first4=Z. |last5=Gulyás |first5=J. |last6=Nagy |first6=Á. |last7=Sas |first7=N. |last8=Timár |first8=J. |last9=Tornyi |first9=T. G. |last10=Vajda |first10=I. |display-authors=3 |title=New results on the <sup>8</sup>Be anomaly |journal=Journal of Physics: Conference Series |date=2018 |volume=1056 |pages=012028 |doi=10.1088/1742-6596/1056/1/012028|url=http://cds.cern.ch/record/2678071/files/pdf.pdf |doi-access=free }}</ref> While further experiments are needed to corroborate these observations, the influence of a fifth boson has been proposed as "the most straightforward possibility".<ref name=5fnews>{{cite news |title=Has a Hungarian physics lab found a fifth force of nature? |last=Cartlidge |first=E. |date=25 May 2016 |accessdate=14 July 2019 |publisher=Nature |url=https://www.nature.com/news/has-a-hungarian-physics-lab-found-a-fifth-force-of-nature-1.19957}}</ref>
+A 2015 experiment by Attila Krasznahorkay et al. at the [[ATOMKI|Hungarian Academy of Sciences's Institute for Nuclear Research]] found anomalous decays in the 17.64 and 18.15&nbsp;MeV excited states of <sup>8</sup>Be, populated by proton irradiation of <sup>7</sup>Li. An excess of decays creating [[electron]]-[[positron]] pairs at a 140° angle with a combined energy of 17&nbsp;MeV was observed. Jonathan Feng et al. attribute this 6.8-[[standard deviation|σ]] anomaly to a 17&nbsp;MeV protophobic X-[[gauge boson|boson]] dubbed the [[X17 particle]]. This boson would mediate a [[fifth force|fifth fundamental force]] acting over a short range (12&nbsp;[[femtometer|fm]]) and perhaps explain the decay of these <sup>8</sup>Be excited states.<ref name=5force/> A 2018 rerun of this experiment found the same anomalous particle scattering and set a narrower mass range of the proposed fifth boson, {{val|17.01|0.16}} [[Electronvolt (mass)|MeV/c<sup>2</sup>]].<ref name=expt18>{{cite journal |last1=Krasznahorkay |first1=A. J. |last2=Csatlós |first2=M. |last3=Csige |first3=L. |last4=Gácsi |first4=Z. |last5=Gulyás |first5=J. |last6=Nagy |first6=Á. |last7=Sas |first7=N. |last8=Timár |first8=J. |last9=Tornyi |first9=T. G. |last10=Vajda |first10=I. |display-authors=3 |title=New results on the <sup>8</sup>Be anomaly |journal=Journal of Physics: Conference Series |date=2018 |volume=1056 |issue=1 |pages=012028 |doi=10.1088/1742-6596/1056/1/012028|bibcode=2018JPhCS1056a2028K |url=https://cds.cern.ch/record/2678071/files/pdf.pdf |doi-access=free }}</ref> While further experiments are needed to corroborate these observations, the influence of a fifth boson has been proposed as "the most straightforward possibility".<ref name=5fnews>{{cite news |title=Has a Hungarian physics lab found a fifth force of nature? |last=Cartlidge |first=E. |date=25 May 2016 |accessdate=14 July 2019 |publisher=Nature |url=https://www.nature.com/news/has-a-hungarian-physics-lab-found-a-fifth-force-of-nature-1.19957}}</ref>
 == Role in stellar nucleosynthesis ==
-In [[stellar nucleosynthesis]], two [[helium-4]] nuclei may collide and [[Nuclear fusion|fuse]] into a single beryllium-8 nucleus. Beryllium-8 has an extremely short half-life (8.19{{e|−17}}&nbsp;seconds), and [[Radioactive decay|decays]] back into two helium-4 nuclei. This, along with the unbound nature of <sup>5</sup>He and <sup>5</sup>Li, creates a bottleneck in [[Big Bang nucleosynthesis]] and [[stellar nucleosynthesis]],<ref name=8gap/> for it necessitates a very fast reaction rate.<ref name=exft>{{cite arxiv |last=Landsman |first=K. |title=The Fine-Tuning Argument |date=2015 |eprint=1505.05359|class=physics.hist-ph }}</ref> This impedes formation of heavier elements in the former, and limits the yield in the latter process. If the beryllium-8 collides with a helium-4 nucleus before decaying, they can fuse into a [[carbon-12]] nucleus. This reaction was first theorized independently by Öpik<ref>{{cite journal |last=Öpik |first=E. J. |author-link=Ernst Öpik|date=1951 |title=Stellar Models with Variable Composition. II. Sequences of Models with Energy Generation Proportional to the Fifteenth Power of Temperature |journal=Proceedings of the Royal Irish Academy, Section A |volume=54 |pages=49–77 |jstor=20488524}}</ref> and Salpeter<ref>{{cite journal |last=Salpeter |first=E. E. |date=1952 |title=Nuclear Reactions in the Stars. I. Proton-Proton Chain". |journal=[[Physical Review]] |volume=88 |issue=3 |pages=547–553 |doi=10.1103/PhysRev.88.547}}</ref> in the early 1950s.
+In [[stellar nucleosynthesis]], two [[helium-4]] nuclei may collide and [[Nuclear fusion|fuse]] into a single beryllium-8 nucleus. Beryllium-8 has an extremely short half-life (8.19{{e|−17}}&nbsp;seconds), and [[Radioactive decay|decays]] back into two helium-4 nuclei. This, along with the unbound nature of <sup>5</sup>He and <sup>5</sup>Li, creates a bottleneck in [[Big Bang nucleosynthesis]] and [[stellar nucleosynthesis]],<ref name=8gap/> for it necessitates a very fast reaction rate.<ref name=exft>{{cite arXiv |last=Landsman |first=K. |title=The Fine-Tuning Argument |date=2015 |eprint=1505.05359|class=physics.hist-ph }}</ref> This impedes formation of heavier elements in the former, and limits the yield in the latter process. If the beryllium-8 collides with a helium-4 nucleus before decaying, they can fuse into a [[carbon-12]] nucleus. This reaction was first theorized independently by Öpik<ref>{{cite journal |last=Öpik |first=E. J. |author-link=Ernst Öpik|date=1951 |title=Stellar Models with Variable Composition. II. Sequences of Models with Energy Generation Proportional to the Fifteenth Power of Temperature |journal=Proceedings of the Royal Irish Academy, Section A |volume=54 |pages=49–77 |jstor=20488524}}</ref> and Salpeter<ref>{{cite journal |last=Salpeter |first=E. E. |date=1952 |title=Nuclear Reactions in the Stars. I. Proton-Proton Chain". |journal=[[Physical Review]] |volume=88 |issue=3 |pages=547–553 |doi=10.1103/PhysRev.88.547|bibcode=1952PhRv...88..547S }}</ref> in the early 1950s.
-Owing to the instability of <sup>8</sup>Be, the [[triple-alpha process]] is the only reaction in which <sup>12</sup>C and heavier elements may be produced in observed quantities. The triple-alpha process, despite being a three-body reaction, is facilitated when <sup>8</sup>Be production increases such that its concentration is approximately 10<sup>−8</sup> relative to <sup>4</sup>He;<ref name=bld>{{cite web |last=Piekarewicz |first=J. |title=The Birth, Life, and Death of Stars |date=2014 |url=https://web2.physics.fsu.edu/~piekarewicz/OLLI-Lecture2.pdf |accessdate=13 July 2019 |publisher=Florida State University}}</ref> this occurs when <sup>8</sup>Be is produced faster than it decays.<ref name=rcap>{{cite journal |last1=Sadeghi |first1=H. |last2=Pourimani |first2=R. |last3=Moghadasi |first3=A. |title=Two-helium radiative capture process and the <sup>8</sup>Be nucleus at settler energies |journal=Astrophysics and Space Science |date=2014 |volume=350 |issue=2 |pages=707–712 |doi=10.1007/s10509-014-1806-1 |url=https://www.researchgate.net/publication/260518982}}</ref> However, this alone is insufficient, as the collision between <sup>8</sup>Be and <sup>4</sup>He is more likely to break apart the system rather than enable fusion;<ref name=gizmodo>{{cite web |last1=Inglis-Arkell |first1=E. |title=This Unbelievable Coincidence Is Responsible For Life In The Universe |url=https://io9.gizmodo.com/this-unbelievable-coincidence-is-responsible-for-life-i-1709731652 |publisher=Gizmodo |accessdate=14 July 2019}}</ref> the reaction rate would still not be fast enough to explain the observed abundance of <sup>12</sup>C.<ref name=otheru>{{cite journal |last1=Adams |first1=F. C. |last2=Grohs |first2=E. |title=Stellar helium burning in other universes: A solution to the triple alpha fine-tuning problem |date=2017 |journal=Astroparticle Physics |volume=7 |pages=40–54 |doi=10.1016/j.astropartphys.2016.12.002 |arxiv=1608.04690}}</ref> In 1954, [[Fred Hoyle]] thus postulated the existence of a [[resonance (particle physics)|resonance]] in carbon-12 within the stellar energy region of the triple-alpha process, enhancing the creation of carbon-12 despite the extremely short half-life of beryllium-8.<ref>Hoyle, F. (1954). "On Nuclear Reactions Occurring in Very Hot STARS. I. the Synthesis of Elements from Carbon to Nickel". ''[[Astrophysical Journal Supplement]].'' '''1''': 121–146, {{doi|10.1086/190005}}</ref> The existence of this resonance (the [[Hoyle state]]) was  confirmed experimentally shortly thereafter; its discovery has been cited in formulations of the [[anthropic principle]] and the fine-tuned Universe hypothesis.<ref name=hoyles>{{cite journal |last1=Epelbaum |first1=E. |last2=Krebs |first2=H. |last3=Lee |first3=D. |last4=Meißner |first4=Ulf-G. |s2cid=33827991 |date=2011 |title=''Ab initio'' calculation of the Hoyle state |journal=Physical Review Letters |volume=106 |issue=19 |pages=192501–1–192501–4 |doi=10.1103/PhysRevLett.106.192501 |pmid=21668146 |doi-access=free }}</ref><ref>{{Cite web|last=Jenkins|first=David|last2=Kirsebom|first2=Oliver|date=2013-02-07|title=The secret of life|url=https://physicsworld.com/a/the-secret-of-life/|url-status=live|access-date=2021-08-21|website=Physics World|language=en-GB}}</ref>
+Owing to the instability of <sup>8</sup>Be, the [[triple-alpha process]] is the only reaction in which <sup>12</sup>C and heavier elements may be produced in observed quantities. The triple-alpha process, despite being a three-body reaction, is facilitated when <sup>8</sup>Be production increases such that its concentration is approximately 10<sup>−8</sup> relative to <sup>4</sup>He;<ref name=bld>{{cite web |last=Piekarewicz |first=J. |title=The Birth, Life, and Death of Stars |date=2014 |url=https://web2.physics.fsu.edu/~piekarewicz/OLLI-Lecture2.pdf |accessdate=13 July 2019 |publisher=Florida State University}}</ref> this occurs when <sup>8</sup>Be is produced faster than it decays.<ref name=rcap>{{cite journal |last1=Sadeghi |first1=H. |last2=Pourimani |first2=R. |last3=Moghadasi |first3=A. |title=Two-helium radiative capture process and the <sup>8</sup>Be nucleus at settler energies |journal=Astrophysics and Space Science |date=2014 |volume=350 |issue=2 |pages=707–712 |doi=10.1007/s10509-014-1806-1 |bibcode=2014Ap&SS.350..707S |s2cid=123444620 |url=https://www.researchgate.net/publication/260518982}}</ref> However, this alone is insufficient, as the collision between <sup>8</sup>Be and <sup>4</sup>He is more likely to break apart the system rather than enable fusion;<ref name=gizmodo>{{cite web |last1=Inglis-Arkell |first1=E. |title=This Unbelievable Coincidence Is Responsible For Life In The Universe |url=https://io9.gizmodo.com/this-unbelievable-coincidence-is-responsible-for-life-i-1709731652 |publisher=Gizmodo |accessdate=14 July 2019}}</ref> the reaction rate would still not be fast enough to explain the observed abundance of <sup>12</sup>C.<ref name=otheru>{{cite journal |last1=Adams |first1=F. C. |last2=Grohs |first2=E. |title=Stellar helium burning in other universes: A solution to the triple alpha fine-tuning problem |date=2017 |journal=Astroparticle Physics |volume=7 |pages=40–54 |doi=10.1016/j.astropartphys.2016.12.002 |arxiv=1608.04690|bibcode=2017APh....87...40A |s2cid=119287629 }}</ref> In 1954, [[Fred Hoyle]] thus postulated the existence of a [[resonance (particle physics)|resonance]] in carbon-12 within the stellar energy region of the triple-alpha process, enhancing the creation of carbon-12 despite the extremely short half-life of beryllium-8.<ref>Hoyle, F. (1954). "On Nuclear Reactions Occurring in Very Hot STARS. I. the Synthesis of Elements from Carbon to Nickel". ''[[Astrophysical Journal Supplement]].'' '''1''': 121–146, {{doi|10.1086/190005}}</ref> The existence of this resonance (the [[Hoyle state]]) was  confirmed experimentally shortly thereafter; its discovery has been cited in formulations of the [[anthropic principle]] and the fine-tuned Universe hypothesis.<ref name=hoyles>{{cite journal |last1=Epelbaum |first1=E. |last2=Krebs |first2=H. |last3=Lee |first3=D. |last4=Meißner |first4=Ulf-G. |s2cid=33827991 |date=2011 |title=''Ab initio'' calculation of the Hoyle state |journal=Physical Review Letters |volume=106 |issue=19 |pages=192501–1–192501–4 |doi=10.1103/PhysRevLett.106.192501 |pmid=21668146 |arxiv=1101.2547 |bibcode=2011PhRvL.106s2501E |doi-access=free }}</ref><ref>{{Cite web|last1=Jenkins|first1=David|last2=Kirsebom|first2=Oliver|date=2013-02-07|title=The secret of life|url=https://physicsworld.com/a/the-secret-of-life/|url-status=live|access-date=2021-08-21|website=Physics World|language=en-GB|archive-url=https://web.archive.org/web/20210213104419/https://physicsworld.com/a/the-secret-of-life/ |archive-date=2021-02-13 }}</ref>
 == Hypothetical universes with stable <sup>8</sup>Be ==
-As beryllium-8 is unbound by only 92 keV, it is theorized that very small changes in [[nuclear potential]] and the fine tuning of certain constants (such as α, the [[fine structure constant]]), could sufficiently increase the binding energy of <sup>8</sup>Be to prevent its alpha decay, thus making it [[stable nuclide|stable]]. This has led to investigations of hypothetical scenarios in which <sup>8</sup>Be is stable and speculation about [[multiverse|other universes]] with different fundamental constants.<ref name=otheru/> These studies suggest that the disappearance of the bottleneck<ref name=hoyles/> created by <sup>8</sup>Be would result in a very different reaction mechanism in [[Big Bang nucleosynthesis]] and the triple-alpha process, as well as alter the abundances of heavier chemical elements.<ref name=a58/> As Big Bang nucleosynthesis only occurred within a short period having the necessary conditions, it is thought that there would be no significant difference in carbon production even if <sup>8</sup>Be were stable.<ref name=8gap>{{cite journal |last1=Coc |first1=A. |last2=Vangioni |first2=E. |title=The triple-alpha reaction and the ''A'' = 8 gap in BBN and Population III stars |journal=Memorie della Società Astronomica Italiana |volume=85 |pages=124–129 |date=2014 |bibcode=2014MmSAI..85..124C |url=http://inspirehep.net/record/1338211/files/2014MmSAI..85..124C.pdf?version=1}}</ref> However, stable <sup>8</sup>Be would enable alternative reaction pathways in helium burning (such as <sup>8</sup>Be + <sup>4</sup>He and <sup>8</sup>Be + <sup>8</sup>Be; constituting a "beryllium burning" phase) and possibly affect the abundance of the resultant <sup>12</sup>C, <sup>16</sup>O, and heavier nuclei, though <sup>1</sup>H and <sup>4</sup>He would remain the most abundant nuclides. This would also affect [[stellar evolution]] through an earlier onset and faster rate of helium burning (and beryllium burning), and result in a different [[main sequence]] than our Universe.<ref name=otheru/>
+As beryllium-8 is unbound by only 92&nbsp;keV, it is theorized that very small changes in [[nuclear potential]] and the fine tuning of certain constants (such as α, the [[fine structure constant]]), could sufficiently increase the binding energy of <sup>8</sup>Be to prevent its alpha decay, thus making it [[stable nuclide|stable]]. This has led to investigations of hypothetical scenarios in which <sup>8</sup>Be is stable and speculation about [[multiverse|other universes]] with different fundamental constants.<ref name=otheru/> These studies suggest that the disappearance of the bottleneck<ref name=hoyles/> created by <sup>8</sup>Be would result in a very different reaction mechanism in [[Big Bang nucleosynthesis]] and the triple-alpha process, as well as alter the abundances of heavier chemical elements.<ref name=a58/> As Big Bang nucleosynthesis only occurred within a short period having the necessary conditions, it is thought that there would be no significant difference in carbon production even if <sup>8</sup>Be were stable.<ref name=8gap>{{cite journal |last1=Coc |first1=A. |last2=Vangioni |first2=E. |title=The triple-alpha reaction and the ''A''&nbsp;=&nbsp;8 gap in BBN and Population III stars |journal=Memorie della Società Astronomica Italiana |volume=85 |pages=124–129 |date=2014 |bibcode=2014MmSAI..85..124C |url=http://inspirehep.net/record/1338211/files/2014MmSAI..85..124C.pdf?version=1}}</ref> However, stable <sup>8</sup>Be would enable alternative reaction pathways in helium burning (such as <sup>8</sup>Be + <sup>4</sup>He and <sup>8</sup>Be + <sup>8</sup>Be; constituting a "beryllium burning" phase) and possibly affect the abundance of the resultant <sup>12</sup>C, <sup>16</sup>O, and heavier nuclei, though <sup>1</sup>H and <sup>4</sup>He would remain the most abundant nuclides. This would also affect [[stellar evolution]] through an earlier onset and faster rate of helium burning (and beryllium burning), and result in a different [[main sequence]] than our Universe.<ref name=otheru/>
 == Notes ==
@@ Line 58: / Line 57: @@
 {{Reflist}}
-{{Isotope|element=beryllium
+{{Isotope sequence
+|element=beryllium
 |lighter=[[beryllium-7]]
 |heavier=[[beryllium-9]]
-|before=[[carbon-9]] '''([[Beta decay|β<sup>+</sup>]], [[proton emission|p]])<br />'''[[boron-9]] '''([[proton emission|p]])<br />'''[[lithium-8]] '''([[beta decay|β<sup>−</sup>]])
+|before=[[carbon-9]] '''([[Beta decay|β<sup>+</sup>]], [[proton emission|p]])<br />'''[[boron-9]] '''([[proton emission|p]])<br />'''[[lithium-8]] '''([[beta decay|β<sup>−</sup>]])'''
-|after=[[helium-4]] '''(α)
+|after=[[helium-4]] '''(α)'''
 }}