Isotopes of helium#Heavier helium isotopes

{{Isotopes table

|symbol=He

|refs=NUBASE2020, AME2020 II

|notes=resonance, unc(), var[], daughter-st, spin#, spin(), n, p

}}

|-

| rowspan=2|{{sup|2}}HeIntermediate in the proton–proton chain

| rowspan=2 style="text-align:right" | 2

| rowspan=2 style="text-align:right" | 0

| rowspan="2" | {{val|2.015894|(2)}}

| rowspan=2 | ≪ {{val|e=-9|u=s}}

| p (> {{val|99.99|u=%}})

| {{sup|1}}H

| rowspan=2 | 0+#

| rowspan=2 |

| rowspan=2 |

|-

| Positron emission (< {{val|0.01|u=%}})

| Deuterium

|-

| Helium-3Produced in Big Bang nucleosynthesisThis and {{sup|1}}H are the only stable nuclei with more protons than neutrons

| style="text-align:right" | 2

| style="text-align:right" | 1

| {{val|3.016029321967|(60)}}

| colspan=3 align=center|Stable

| 1/2+

| {{val|0.000002|(2)}}{{cite web |title=Atomic Weight of Helium |publisher=Commission on Isotopic Abundances and Atomic Weights |url=https://ciaaw.org/helium.htm |access-date=6 October 2021 |url-status=live |archive-url=https://web.archive.org/web/20230504051114/https://ciaaw.org/helium.htm |archive-date=4 May 2023}}

| [{{val|4.6|e=-10}}, {{val|0.000041}}]{{cite journal |last1=Meija |first1=Juris |last2=Coplen |first2=Tyler B. |last3=Berglund |first3=Michael |last4=Brand |first4=Willi A. |last5=Bièvre |first5=Paul De |last6=Gröning |first6=Manfred |last7=Holden |first7=Norman E. |last8=Irrgeher |first8=Johanna |last9=Loss |first9=Robert D. |last10=Walczyk |first10=Thomas |last11=Prohaska |first11=Thomas |title=Isotopic compositions of the elements 2013 (IUPAC Technical Report) |date=2016-03-01 |journal=Pure and Applied Chemistry |language=en |volume=88 |issue=3 |pages=293–306 |issn=1365-3075 |doi=10.1515/pac-2015-0503 |doi-access=free |hdl=11858/00-001M-0000-0029-C408-7 |hdl-access=free |s2cid=104472050}}

|-

| Helium-4Produced in alpha decay

| style="text-align:right" | 2

| style="text-align:right" | 2

| {{val|4.002603254130|(158)}}

| colspan=3 align=center|Stable

| 0+

| {{val|0.999998|(2)}}

| [{{val|0.999959}}, {{val|1.000000}}]

|-

| {{sup|5}}He

| style="text-align:right" | 2

| style="text-align:right" | 3

| {{val|5.012057|(21)}}

| {{val|6.02|(22)|e=-22|u=s}}
[{{val|758|(28)|u=keV}}]

| n

| {{sup|4}}He

| 3/2−

|

|

|-

| rowspan=2|{{sup|6}}HeHas 2 halo neutrons

| rowspan=2 style="text-align:right" | 2

| rowspan=2 style="text-align:right" | 4

| rowspan=2|{{val|6.018885889|(57)}}

| rowspan=2|{{val|806.92|(24)|u=ms}}

| Beta decay ({{val|99.999722|(18)}}%)

| {{sup|6}}Li

| rowspan=2|0+

| rowspan=2|

| rowspan=2|

|-

| β{{sup|−}}dd: Deuteron emission ({{val|0.000278|(18)}}%)

| {{sup|4}}He

|-id=Helium-7

| {{sup|7}}He

| style="text-align:right" | 2

| style="text-align:right" | 5

| {{val|7.027991|(8)}}

| {{val|2.51|(7)|e=-21|u=s}}
[{{val|182|(5)|u=keV}}]

| n

| {{sup|6}}He

| (3/2)−

|

|

|-

| rowspan=3|{{sup|8}}HeHas 4 halo neutrons

| rowspan=3 style="text-align:right" | 2

| rowspan=3 style="text-align:right" | 6

| rowspan=3|{{val|8.033934388|(95)}}

| rowspan=3|{{val|119.5|(1.5)|u=ms}}

| β{{sup|−}} ({{val|83.1|(1.0)|u=%}})

| {{sup|8}}Li

| rowspan=3|0+

| rowspan=3|

| rowspan=3|

|-

| β{{sup|−}}n ({{val|16|(1)|u=%}})

| {{sup|7}}Li

|-

| β{{sup|−}}tt: Triton emission ({{val|0.9|(1)|u=%}})

| {{sup|5}}He

|-id=Helium-9

| {{sup|9}}He

| style="text-align:right" | 2

| style="text-align:right" | 7

| {{val|9.043946|(50)}}

| {{val|2.5|(2.3)|e=-21|u=s}}

| n

| {{SimpleNuclide|Helium|8}}

| 1/2(+)

|

|

|-

| {{sup|10}}He

| style="text-align:right" | 2

| style="text-align:right" | 8

| {{val|10.05281531|(10)}}

| {{val|2.60|(40)|e=-22|u=s}}
[{{val|1.76|(27)|u=MeV}}]

| 2n

| {{sup|8}}He

| 0+

|

|

{{Isotopes table/footer}}

{{anchor|Helium-2}}

{{Redirect-distinguish|Helium 2|Helium II|Helium dimer}}

Helium-2, {{sup|2}}He, is extremely unstable. Its nucleus, a diproton, consists of two protons with no neutrons. According to theoretical calculations, it would be much more stable (but still positron emission to deuterium) if the strong force were 2% greater.{{cite journal |last1=Bradford |first1=R. A. W. |title=The effect of hypothetical diproton stability on the universe |journal=Journal of Astrophysics and Astronomy |date=27 August 2009 |volume=30 |issue=2 |pages=119–131 |bibcode=2009JApA...30..119B |citeseerx=10.1.1.495.4545 |doi=10.1007/s12036-009-0005-x |s2cid=122223720 |url=http://rickbradford.co.uk/Diprotons.pdf}} Its instability is due to spin–spin interactions in the nuclear force and the Pauli exclusion principle, which states that within a given quantum system two or more identical particles with the same half-integer spins (that is, fermions) cannot simultaneously occupy the same quantum state; so {{sup|2}}He's two protons have opposite-aligned spins and the diproton itself has negative binding energy.Nuclear Physics in a Nutshell, C. A. Bertulani, Princeton University Press, Princeton, NJ, 2007, Chapter 1, {{ISBN|978-0-691-12505-3}}.

{{sup|2}}He may have been observed. In 2000, physicists first observed a new type of radioactive decay in which a nucleus emits two protons at once—perhaps {{sup|2}}He.[http://physicsworld.com/cws/article/news/2762 Physicists discover new kind of radioactivity] {{Webarchive|url=https://web.archive.org/web/20110423211717/http://physicsworld.com/cws/article/news/2762|date=2011-04-23}}, in [http://physicsworld.com/cws/home physicsworld.com] Oct 24, 2000.{{cite journal |author=J. Gómez del Campo |author2=A. Galindo-Uribarri |display-authors=etal |title=Decay of a Resonance in {{sup|date=2001|18}}Ne by the Simultaneous Emission of Two Protons |journal=Physical Review Letters |volume=86 |issue=2001 |pages=43–46 |doi=10.1103/PhysRevLett.86.43|pmid=11136089|bibcode=2001PhRvL..86...43G}} The team led by Alfredo Galindo-Uribarri of Oak Ridge National Laboratory announced that the discovery will help understand the strong nuclear force and provide fresh insights into stellar nucleosynthesis. Galindo-Uribarri and co-workers chose an isotope of neon with an energy structure that prevents it from emitting protons one at a time. This means the two protons are ejected simultaneously. The team fired a beam of fluorine ions at a proton-rich target to produce {{sup|18}}Ne, which then decayed into oxygen and two protons. Any protons ejected from the target itself were identified by their characteristic energies. The two-proton emission may proceed in two ways: the neon might eject a diproton, which then decays into separate protons, or the protons may be emitted separately but simultaneously in a "democratic decay". The experiment was not sensitive enough to establish which of these two processes was taking place.

More evidence of {{sup|2}}He was found in 2008 at Istituto Nazionale di Fisica Nucleare, in Italy.{{cite journal |last=Schewe |first=Phil |title=New Form of Artificial Radioactivity |date=2008-05-29 |journal=Physics News Update |number=865 #2 |url=http://www.aip.org/pnu/2008/split/865-2.html |url-status=dead |archive-url=https://web.archive.org/web/20081014143925/http://www.aip.org/pnu/2008/split/865-2.html |archive-date=2008-10-14}}{{cite journal |last1=Raciti |first1=G. |last2=Cardella |first2=G. |last3=De Napoli |first3=M. |last4=Rapisarda |first4=E. |last5=Amorini |first5=F. |last6=Sfienti |first6=C. |title=Experimental Evidence of {{sup|date=2008 |2}}He Decay from {{sup|18}}Ne Excited States |journal=Phys. Rev. Lett. |volume=100 |issue=19|pages=192503–192506 |doi=10.1103/PhysRevLett.100.192503 |pmid=18518446 |bibcode=2008PhRvL.100s2503R}} A beam of {{sup|20}}Ne ions was directed at a target of beryllium foil. This collision converted some of the heavier neon nuclei in the beam into {{sup|18}}Ne nuclei. These nuclei then collided with a foil of lead. The second collision excited the {{sup|18}}Ne nucleus into a highly unstable condition. As in the earlier experiment at Oak Ridge, the {{sup|18}}Ne nucleus decayed into an {{sup|16}}O nucleus, plus two protons detected exiting from the same direction. The new experiment showed that the two protons were initially ejected together, correlated in a quasibound term symbol, before decaying into separate protons much less than a nanosecond later.

Further evidence comes from Riken in Japan and Joint Institute for Nuclear Research in Dubna, Russia, where beams of {{sup|6}}He nuclei were directed at a cryogenic hydrogen target to produce {{sup|5}}H. It was discovered that the {{sup|6}}He can donate all four of its neutrons to the hydrogen.{{Citation needed|date=January 2012}} The two remaining protons could be simultaneously ejected from the target as a diproton, which quickly decayed into two protons. A similar reaction has also been observed from {{sup|8}}He nuclei colliding with hydrogen.{{cite journal |title=Experimental Evidence for the Existence of {{sup|7}}H and for a Specific Structure of {{sup|8}}He |author=Korsheninnikov A. A. |display-authors=etal |date=2003-02-28 |journal=Physical Review Letters |volume=90 |issue=8 |pages=082501 |doi=10.1103/PhysRevLett.90.082501 |pmid=12633420 |bibcode=2003PhRvL..90h2501K |url=http://fy.chalmers.se/~f2bmz/papers/korsheninnikov_2003_7h.pdf}}

Under the influence of electromagnetic interactions, the Jaffe-Low primitives

{{cite journal

|last1=Jaffe |first1=R. L.

|last2=Low |first2=F. E.

|year=1979

|title=Connection between quark-model eigenstates and low-energy scattering

|journal=Physical Review D

|volume=19 |issue=7

|pages=2105–2118

|bibcode=1979PhRvD..19.2105J

|doi=10.1103/PhysRevD.19.2105

|url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.19.2105

}}

may leave the unitary cut, creating narrow two-nucleon resonances, like a diproton resonance with a mass of 2000 MeV and a width of a few hundred keV.

{{cite journal

|last1=Krivoruchenko |first1=M. I.

|year=2011

|title=Possibility of narrow resonances in nucleon-nucleon channels

|journal=Physical Review C

|volume=84 |issue=1

|pages=015206

|arxiv=1102.2718

|bibcode=2011PhRvC..84a5206K

|doi=10.1103/PhysRevC.84.015206

|url=https://journals.aps.org/prc/abstract/10.1103/PhysRevC.84.015206

}}

To search for this resonance, a beam of protons with kinetic energy 250 MeV and an energy spread below 100 keV is required, which is feasible considering the electron cooling of the beam.

{{sup|2}}He is an intermediate in the first step of the proton–proton chain. The first step of the proton-proton chain is a two-stage process: first, two protons fuse to form a diproton:

:{{sup|1}}H + {{sup|1}}H + {{val|1.25|ul=MeV}} → {{sup|2}}He;

in a low-probability branch, the diproton beta-plus decays into deuterium:

:{{sup|2}}He → {{sup|2}}H + positron + electron neutrino + {{val|1.67|u=MeV}};

with the overall formula

:{{sup|1}}H + {{sup|1}}H → {{sup|2}}H + e{{sup|+}} + ν{{sub|e}} + {{val|0.42|u=MeV}}.

More than 99.99% of the time the diproton fissions back to two protons. The hypothetical effect of a bound diproton on Big Bang and stellar nucleosynthesis, has been investigated. Some models suggest that variations in the strong force allowing a bound diproton would enable the conversion of all primordial hydrogen to helium in the Big Bang, which would be catastrophic for the development of stars and life. This notion is an example of the anthropic principle. However, a 2009 study suggests that such a conclusion can't be drawn, as the formed diproton would still decay to deuterium, whose binding energy would also increase. In some scenarios, it is postulated that hydrogen (in the form of {{sup|2}}H) could still survive in large amounts, rebutting arguments that the strong force is tuned within a precise anthropic limit.{{cite journal |last1=MacDonald |first1=J. |last2=Mullan |first2=D.J. |title=Big Bang Nucleosynthesis: The strong nuclear force meets the weak anthropic principle |date=2009 |arxiv=0904.1807 |journal=Physical Review D |volume=80 |issue=4 |pages=043507 |bibcode=2009PhRvD..80d3507M |doi=10.1103/PhysRevD.80.043507 |s2cid=119203730}}

{{Main|Helium-3}}

{{sup|3}}He is the only stable isotope other than {{sup|1}}H with more protons than neutrons. (There are many such unstable isotopes; the lightest are {{sup|7}}Be and {{sup|8}}B.) There is only a trace (~2ppm) of {{sup|3}}He on Earth, mainly present since the formation of the Earth, although some falls to Earth trapped in cosmic dust.

{{cite web

|title=Helium Fundamentals

|url=http://www.mantleplumes.org/HeliumFundamentals.html

}} Trace amounts are also produced by the beta decay of tritium.

{{cite web

|author=K. L. Barbalace

|title=Periodic Table of Elements: Li—Lithium

|work=EnvironmentalChemistry.com

|url=http://environmentalchemistry.com/yogi/periodic/Li-pg2.html

|access-date=2010-09-13

}} In stars, however, {{sup|3}}He is more abundant, a product of nuclear fusion. Extraplanetary material, such as lunar and asteroid regolith, has traces of {{sup|3}}He from solar wind bombardment.

To become superfluid, {{sup|3}}He must be cooled to 2.5 millikelvin, ~900 times lower than {{sup|4}}He ({{val|2.17|u=K}}). This difference is explained by quantum statistics: {{sup|3}}He atoms are fermions, while {{sup|4}}He atoms are bosons, which condense to a superfluid more easily.

{{Main|Helium-4}}

The most common isotope, {{sup|4}}He, is produced on Earth by alpha decay of heavier elements; the alpha particles that emerge are fully ionized {{sup|4}}He nuclei. {{sup|4}}He is an unusually stable nucleus because it is doubly magic. It was formed in enormous quantities in Big Bang nucleosynthesis.

Terrestrial helium consists almost exclusively (all but ~2ppm) of {{sup|4}}He. {{sup|4}}He's boiling point of {{val|4.2|u=K}} is the lowest of all known substances except {{sup|3}}He. When cooled further to {{val|2.17|u=K}}, it becomes a unique superfluid with zero viscosity. It solidifies only at pressures above 25 atmospheres, where it melts at {{val|0.95|u=K}}.

File:1987 CPA 5891.jpg tokamak depicts the helium-5 nucleus during deuterium-tritium fusion|left]]

File:Cross Section for Fusion reactions.png

Helium-5 is extremely unstable, decaying to helium-4 with a half-life of 602 yoctoseconds. It is briefly produced in the favorable fusion reaction:

$\{\}^2\backslash mathrm\{D\}\; +\; \{\}^3\backslash mathrm\{T\}\; \backslash longrightarrow\; \{\}^5\backslash mathrm\{He\}^\{*\}\; \backslash longrightarrow\; \{\}^4\backslash mathrm\{He\}\; +\; n\; +\; 17.6\backslash \; \backslash mathrm\{MeV\}$

The reaction is greatly enhanced by the existence of a resonance. Helium-5, which has a natural spin state of -3/2 at the 0 MeV ground state, has a +3/2 excited spin state at 16.84 MeV. Because the reaction creates helium-5 nuclei with an energy level close to this state, it happens more frequently. This was discovered by Egon Bretscher, a scientist investigating weaponization of fusion reactions for the Manhattan Project.

The DT reaction specifically is 100 times more likely than the DD reaction at relevant energies, but would be similar without the resonance. The D-3He reaction benefits from a similar resonance in lithium-5, but is Coulomb-suppressed i.e. the +2 helium nucleus charge increases the electrostatic repulsion for fusing nuclei.{{cite arXiv|eprint=2305.00647 |title=DT fusion through the ⁵He 3/2⁺ "Bretscher state" accounts for ≥25% of our existence via nucleosynthesis and for the possibility of fusion energy |last1=Chadwick |first1=Mark B. |last2=Paris |first2=Mark W. |last3=Haines |first3=Brian M. |date=2023 |class=physics.hist-ph }}

{{anchor|Helium-6|Helium-8}}

Helium-6 is the longest-lived radioactive isotope of helium; it beta decays with a half-life of 806.92 milliseconds. The most widely studied heavy helium isotope is {{sup|8}}He,{{cn|date=April 2025}} which beta decays with a half-life of 119.5 milliseconds. {{sup|6}}He and {{sup|8}}He are thought to consist of a normal {{sup|4}}He nucleus surrounded by a neutron "halo" (of two neutrons in {{sup|6}}He and four neutrons in {{sup|8}}He). The unusual structues of halo nuclei may offer insights into the isolated properties of neutrons and physics beyond the Standard Model.{{cite web |title=Helium-8 study gives insight into nuclear theory, neutron stars |date=2008-01-25 |language=en |publisher=Argonne National Laboratory |website=anl.gov |url=https://www.anl.gov/article/helium8-study-gives-insight-into-nuclear-theory-neutron-stars |access-date=2023-09-10}}{{cite web |title=Radioactive beams drive physics forward |date=1999-11-29 |language=en-GB |website=CERN Courier |url=https://cerncourier.com/a/radioactive-beams-drive-physics-forward/ |access-date=2023-09-10}}

The shortest-lived and heaviest known helium isotope is {{sup|10}}He. Despite being a doubly magic isotope, {{sup|10}}He is not particle-bound and near-instantly drips out two neutrons (half-life ~260 yoctoseconds).{{cite book |author=Clifford A. Hampel |year=1968 |title=The Encyclopedia of the Chemical Elements |page=[https://archive.org/details/encyclopediaofch00hamp/page/260 260] |publisher=Reinhold Book Corporation |isbn=978-0278916432 |url=https://archive.org/details/encyclopediaofch00hamp |url-access=registration}}

{{Reflist}}

• [https://web.archive.org/web/20191222181359/https://tunl.duke.edu/nucldata/General_Tables/General_Tables.shtml General Tables] — abstracts for helium and other exotic light nuclei

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Category:Helium

Helium