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Isotopes of helium

From Wikipedia, the free encyclopedia

Isotopes ofhelium (2He)
Main isotopes[1]Decay
Isotopeabun­dancehalf-life(t1/2)modepro­duct
3He0.0002%stable
4He99.9998%stable
Standard atomic weightAr°(He)

Helium (2He) has nine knownisotopes, but onlyhelium-3 (3He) andhelium-4 (4He) arestable. Allradioisotopes are short-lived; the only particle-bound ones are6He and8He withhalf-lives 806.9 and 119.5 milliseconds.

In Earth's atmosphere, the ratio of3He to4He is1.37×10−6.[2] However, the isotopic abundance of helium varies greatly depending on its origin, though helium-4 is always in great preponderance. In theLocal Interstellar Cloud, the proportion of3He to4He is1.62(29)×10−4,[4] which is about 120 times higher than in Earth's atmosphere. Rocks from Earth's crust have isotope ratios varying by as much as a factor of ten; this is used ingeology to investigate the origin of rocks and the composition of the Earth'smantle.[5] The different formation processes of the two stable isotopes of helium produce the differing isotope abundances.

Equal mixtures of liquid3He and4He below0.8 K separate into twoimmiscible phases due to differences inquantum statistics:4He atoms arebosons while3He atoms arefermions.[6]Dilution refrigerators take advantage of the immiscibility of these two isotopes to achieve temperatures as low as a few millikelvin.

A mix of the two isotopes spontaneously separates into3He-rich and4He-rich regions.[7] Phase separation also exists inultracold gas systems.[8] It has been shown experimentally in a two-component ultracoldFermi gas case.[9][10] The phase separation can compete with other phenomena asvortex lattice formation or an exoticFulde–Ferrell–Larkin–Ovchinnikov phase.[11]

List of isotopes

[edit]
Nuclide
ZNIsotopic mass(Da)[12]
[n 1]		Half-life[1]

[resonance width]		Decay
mode[1]
[n 2]		Daughter
isotope
[n 3]		Spin and
parity[1]
[n 4][n 5]		Natural abundance(mole fraction)
Normal proportion[1]Range of variation
2He[n 6]202.015894(2)≪10−9 s[13]p (>99.99%)1H0+#
β+ (<0.01%)2H
3He[n 6][n 7][n 8]213.016029321967(60)Stable1/2+0.000002(2)[2][4.6×10−10,0.000041][14]
4He[n 7][n 9]224.002603254130(158)Stable0+0.999998(2)[2][0.999959,1.000000][14]
5He235.012057(21)6.02(22)×10−22 s
[758(28) keV]		n4He3/2−
6He[n 10]246.018885889(57)806.92(24) msβ− (99.999722(18)%)6Li0+
β−d[n 11] (0.000278(18)%)4He
7He257.027991(8)2.51(7)×10−21 s
[182(5) keV]		n6He(3/2)−
8He[n 12]268.033934388(95)119.5(1.5) msβ− (83.1(1.0)%)8Li0+
β−n (16(1)%)7Li
β−t[n 13] (0.9(1)%)5He
9He279.043946(50)2.5(2.3)×10−21 sn8
He		1/2(+)
10He2810.05281531(10)2.60(40)×10−22 s
[1.76(27) MeV]		2n8He0+
This table header & footer:
  1. ^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. ^Modes of decay:
    n:Neutron emission
    p:Proton emission
  3. ^Bold symbol as daughter – Daughter product is stable.
  4. ^( ) spin value – Indicates spin with weak assignment arguments.
  5. ^# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  6. ^abIntermediate in theproton–proton chain
  7. ^abProduced inBig Bang nucleosynthesis
  8. ^This and1H are the only stable nuclei with more protons than neutrons
  9. ^Produced inalpha decay
  10. ^Has 2halo neutrons
  11. ^d: Deuteron emission
  12. ^Has 4 halo neutrons
  13. ^t:Triton emission

Helium-2 (diproton)

[edit]
"Helium 2" redirects here; not to be confused withHelium II orHelium dimer.

Helium-2,2He, is unbound. The only bound atom with amass number of 2 isdeuterium.[15][16] The nucleus of2He, adiproton, consists of twoprotons with noneutrons. Its instability is due to spin–spin interactions in thenuclear force and thePauli exclusion principle, which states that within a givenquantum system two or more identical particles with the same half-integer spins (fermions) cannot simultaneously occupy the same quantum state; so2He's two protons have opposite-aligned spins and the diproton itself has negativebinding energy.[17]

A rare form of radioactivity is diproton emission, where a nucleus emits two protons in a quasi-bound1S0 configuration, which then separate.[18] In 2000,Oak Ridge National Laboratory detected two-proton emission from18
10Ne, produced by a17
9F ion beam onto a proton-rich target. But the experiment didn't have the sensitivity to distinguish if the emission was a decay by two separate protons, or by a diproton.[19][20] In 2008, theIstituto Nazionale di Fisica Nucleare confirmed18Ne decayed to a diproton with a 31%branching ratio.[13][21] Several experiments have since detected diproton emission from other isotopes.[18]

The lack of a bound diproton has been used to argue forfine-tuning for the development of life due to its effect onBig Bang nucleosynthesis andstellar evolution.[22][23] Hypothetical models suggest that if the strong force was 2% greater, then diprotons would be bound (but stillβ+ decay todeuterium).[24] Recent studies have found that a universe with bound diprotons doesn’t preclude the development of stars and life.[24][23][16]

One impact of a hypothetical bound diproton is a change to the early steps of the proton-proton chain. In our universe, the first step of the proton-proton chain proceeds via the weak force,[25][26]

p +p →2
1D +e+
 +ν
e +0.42 MeV

In the hypothetical, instead a diproton can form without the weak force,[16][24]

p +p →2
2He

The diproton would thenbeta-plus decays intodeuterium:

2
2He →2
1D +e+
 +ν
e.

With the overall formula,

p +p →2
1D +e+
 +ν
e.

Under the influence ofelectromagnetic interactions, the Jaffe-Low primitives[27] 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.[28] 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.

Helium-3

[edit]
Main article:Helium-3

3He is the only stable isotope other than1H with more protons than neutrons. There are many such unstable isotopes, such as7Be and8B. There is only a trace (~2ppm)[2] of3He on Earth, mainly present since the formation of the Earth, although some falls to Earth trapped in cosmic dust.[5] Trace amounts are also produced by thebeta decay oftritium.[29] Instars, however,3He is more abundant, a product ofnuclear fusion. Extraplanetary material, such aslunar andasteroidregolith, has traces of3He fromsolar wind bombardment.

To becomesuperfluid,3He must be cooled to 2.5 millikelvin, ~900 times lower than4He (2.17 K). This difference is explained byquantum statistics:3He atoms arefermions, while4He atoms arebosons, which condense to a superfluid more easily.

Helium-4

[edit]
Main article:Helium-4

The most common isotope,4He, is produced on Earth byalpha decay of heavier elements; thealpha particles that emerge are fully ionized4He nuclei.4He is an unusually stable nucleus because it isdoubly magic. It was formed in enormous quantities inBig Bang nucleosynthesis.

Terrestrial helium consists almost exclusively (all but ~2ppm)[2] of4He.4He's boiling point of4.2 K is the lowest of all known substances except3He. When cooled further to2.17 K, it becomes a uniquesuperfluid with zeroviscosity. It solidifies only at pressures above 25 atmospheres, where it melts at0.95 K.

Helium-5

[edit]
A 1987 Soviet stamp celebrating theT-15 tokamak depicts the helium-5 nucleus duringdeuterium–tritium fusion
Fusion cross sections of major reactions. Without the resonance in helium-5, the DT reaction would be similar to the DD reaction.

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:

2H+3H⟶5He∗⟶4He+n+17.6 MeV{\displaystyle {}^{2}\mathrm {H} +{}^{3}\mathrm {H} \longrightarrow {}^{5}\mathrm {He} ^{*}\longrightarrow {}^{4}\mathrm {He} +n+17.6\ \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 byEgon Bretscher, who was investigating weaponization of fusion reactions for theManhattan Project.

The DT reaction specifically is 100 times more likely than the DD reaction at relevant energies, but would be similar without the resonance. The2H-3He reaction benefits from a similar resonance inlithium-5, but isCoulomb-suppressed i.e. the +2 helium nucleus charge increases the electrostatic repulsion for fusing nuclei.[30]

Helium-6 and helium-8

[edit]

These are the long-lived radioactive isotope of helium; helium-6beta decays with a half-life of 806.9 milliseconds, and helium-8 with a half-life of 119.5 milliseconds, though additional particle emission is possible and significant for the latter.6He and8He are thought to consist of a normal4He nucleus surrounded by a neutron "halo" (of two neutrons in6He and four neutrons in8He). The unusual structures of halo nuclei may offer insights into the isolated properties ofneutrons andphysics beyond the Standard Model.[31][32]

See also

[edit]

Daughter products other than helium

References

[edit]
  1. ^abcdeKondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021)."The NUBASE2020 evaluation of nuclear properties"(PDF).Chinese Physics C.45 (3) 030001.doi:10.1088/1674-1137/abddae.
  2. ^abcdef"Standard Atomic Weights: Helium".CIAAW. 1983.
  3. ^Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04)."Standard atomic weights of the elements 2021 (IUPAC Technical Report)".Pure and Applied Chemistry.doi:10.1515/pac-2019-0603.ISSN 1365-3075.
  4. ^Busemann, H.; Bühler, F.; Grimberg, A.; Heber, V. S.; Agafonov, Y. N.; Baur, H.; Bochsler, P.; Eismont, N. A.; Wieler, R.; Zastenker, G. N. (2006-03-01)."Interstellar Helium Trapped with the COLLISA Experiment on the MiR Space Station—Improved Isotope Analysis by In Vacuo Etching".The Astrophysical Journal.639 (1): 246.Bibcode:2006ApJ...639..246B.doi:10.1086/499223.ISSN 0004-637X.S2CID 120648440.
  5. ^ab"Helium Fundamentals".
  6. ^The Encyclopedia of the Chemical Elements. p. 264.
  7. ^Pobell, Frank (2007).Matter and methods at low temperatures (3rd rev. and expanded ed.). Berlin: Springer.ISBN 978-3-540-46356-6.OCLC 122268227.
  8. ^Carlson, J.; Reddy, Sanjay (2005-08-02). "Asymmetric Two-Component Fermion Systems in Strong Coupling".Physical Review Letters.95 (6) 060401.arXiv:cond-mat/0503256.Bibcode:2005PhRvL..95f0401C.doi:10.1103/PhysRevLett.95.060401.PMID 16090928.S2CID 448402.
  9. ^Shin, Y.; Zwierlein, M. W.; Schunck, C. H.; Schirotzek, A.; Ketterle, W. (2006-07-18). "Observation of Phase Separation in a Strongly Interacting Imbalanced Fermi Gas".Physical Review Letters.97 (3) 030401.arXiv:cond-mat/0606432.Bibcode:2006PhRvL..97c0401S.doi:10.1103/PhysRevLett.97.030401.PMID 16907486.S2CID 11323402.
  10. ^Zwierlein, Martin W.; Schirotzek, André; Schunck, Christian H.; Ketterle, Wolfgang (2006-01-27). "Fermionic Superfluidity with Imbalanced Spin Populations".Science.311 (5760):492–496.arXiv:cond-mat/0511197.Bibcode:2006Sci...311..492Z.doi:10.1126/science.1122318.ISSN 0036-8075.PMID 16373535.S2CID 13801977.
  11. ^Kopyciński, Jakub; Pudelko, Wojciech R.; Wlazłowski, Gabriel (2021-11-23). "Vortex lattice in spin-imbalanced unitary Fermi gas".Physical Review A.104 (5) 053322.arXiv:2109.00427.Bibcode:2021PhRvA.104e3322K.doi:10.1103/PhysRevA.104.053322.S2CID 237372963.
  12. ^Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*".Chinese Physics C.45 (3) 030003.doi:10.1088/1674-1137/abddaf.
  13. ^abSchewe, Phil (2008-05-29)."New Form of Artificial Radioactivity".Physics News Update (865 #2). Archived fromthe original on 2008-10-14.
  14. ^abMeija, Juris; Coplen, Tyler B.; Berglund, Michael; Brand, Willi A.; Bièvre, Paul De; Gröning, Manfred; Holden, Norman E.; Irrgeher, Johanna; Loss, Robert D.; Walczyk, Thomas; Prohaska, Thomas (2016-03-01)."Isotopic compositions of the elements 2013 (IUPAC Technical Report)".Pure and Applied Chemistry.88 (3):293–306.doi:10.1515/pac-2015-0503.hdl:11858/00-001M-0000-0029-C408-7.ISSN 1365-3075.S2CID 104472050.
  15. ^Loveland, Walter D. (2017).Modern Nuclear Chemistry. New York Academy of Sciences Series (1st ed.). Newark: John Wiley & Sons, Incorporated.ISBN 978-1-119-32838-4.
  16. ^abcAdams, Fred C.; Howe, Alex R.; Grohs, Evan; Fuller, George M. (2021-07-01)."Effects of bound diprotons and enhanced nuclear reaction rates on stellar evolution".Astroparticle Physics.130 102584.arXiv:2103.15744.Bibcode:2021APh...13002584A.doi:10.1016/j.astropartphys.2021.102584.ISSN 0927-6505.
  17. ^Nuclear Physics in a Nutshell, C. A. Bertulani, Princeton University Press, Princeton, NJ, 2007, Chapter 1,ISBN 978-0-691-12505-3.
  18. ^abZhou, Long; Wang, Si-Min; Fang, De-Qing; Ma, Yu-Gang (2022-08-22)."Recent progress in two-proton radioactivity".Nuclear Science and Techniques.33 (8) 105.arXiv:2208.10394.Bibcode:2022NuScT..33..105Z.doi:10.1007/s41365-022-01091-1.ISSN 1001-8042.
  19. ^J. Gómez del Campo; A. Galindo-Uribarri; et al. (2001). "Decay of a Resonance in18Ne by the Simultaneous Emission of Two Protons".Physical Review Letters.86 (2001):43–46.Bibcode:2001PhRvL..86...43G.doi:10.1103/PhysRevLett.86.43.PMID 11136089.
  20. ^Physicists discover new kind of radioactivityArchived 2011-04-23 at theWayback Machine, inphysicsworld.com Oct 24, 2000.
  21. ^Raciti, G.; Cardella, G.; De Napoli, M.; Rapisarda, E.; Amorini, F.; Sfienti, C. (2008). "Experimental Evidence of2He Decay from18Ne Excited States".Phys. Rev. Lett.100 (19) 192503:192503–192506.Bibcode:2008PhRvL.100s2503R.doi:10.1103/PhysRevLett.100.192503.PMID 18518446.
  22. ^Adams, Fred C. (2019-05-15)."The degree of fine-tuning in our universe — and others".Physics Reports.807:1–111.arXiv:1902.03928.Bibcode:2019PhR...807....1A.doi:10.1016/j.physrep.2019.02.001.ISSN 0370-1573.
  23. ^abMacDonald, J.; Mullan, D.J. (2009). "Big Bang Nucleosynthesis: The strong nuclear force meets the weak anthropic principle".Physical Review D.80 (4) 043507.arXiv:0904.1807.Bibcode:2009PhRvD..80d3507M.doi:10.1103/PhysRevD.80.043507.S2CID 119203730.
  24. ^abcBradford, R. A. W. (27 August 2009)."The effect of hypothetical diproton stability on the universe"(PDF).Journal of Astrophysics and Astronomy.30 (2):119–131.Bibcode:2009JApA...30..119B.CiteSeerX 10.1.1.495.4545.doi:10.1007/s12036-009-0005-x.S2CID 122223720.
  25. ^Iliadis, Christian (2015).Nuclear Physics of Stars. New York Academy of Sciences Series (2nd ed.). Newark: John Wiley & Sons, Incorporated.ISBN 978-3-527-33648-7.
  26. ^Dunlap, Richard A. (2023).An Introduction to the Physics of Nuclei and Particles. IOP Ebooks Series (2nd ed.). Bristol: Institute of Physics Publishing.ISBN 978-0-7503-6096-8.
  27. ^Jaffe, R. L.; Low, F. E. (1979)."Connection between quark-model eigenstates and low-energy scattering".Physical Review D.19 (7):2105–2118.Bibcode:1979PhRvD..19.2105J.doi:10.1103/PhysRevD.19.2105.
  28. ^Krivoruchenko, M. I. (2011)."Possibility of narrow resonances in nucleon-nucleon channels".Physical Review C.84 (1) 015206.arXiv:1102.2718.Bibcode:2011PhRvC..84a5206K.doi:10.1103/PhysRevC.84.015206.
  29. ^K. L. Barbalace."Periodic Table of Elements: Li—Lithium".EnvironmentalChemistry.com. Retrieved2010-09-13.
  30. ^Chadwick, Mark B.; Paris, Mark W.; Haines, Brian M. (2023). "DT fusion through the5He 3/2+ "Bretscher state" accounts for ≥25% of our existence via nucleosynthesis and for the possibility of fusion energy".arXiv:2305.00647 [physics.hist-ph].
  31. ^"Helium-8 study gives insight into nuclear theory, neutron stars".anl.gov. Argonne National Laboratory. 2008-01-25. Retrieved2023-09-10.
  32. ^"Radioactive beams drive physics forward".CERN Courier. 1999-11-29. Retrieved2023-09-10.
Group12 3456789101112131415161718
PeriodHydrogen and
alkali metals		Alkaline
earth metals		Pnicto­gensChal­co­gensHalo­gensNoble gases
①12
②345678910
③1112131415161718
④192021222324252627282930313233343536
⑤373839404142434445464748495051525354
⑥55561 asterisk71727374757677787980818283848586
⑦87881 asterisk103104105106107108109110111112113114115116117118
⑧119120
1 asterisk5758596061626364656667686970 
1 asterisk8990919293949596979899100101102
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