Talk:Isotopes of helium

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This article is part of Wikipedia:Wikiproject Isotopes. Please keep style and phrasings consistent across the set of pages. For later reference and improved reliability, data from all considered multiple sources is collected here. References are denoted by these letters:

  • (A) G. Audi, O. Bersillon, J. Blachot, A.H. Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003). — Where this source indicates a speculative value, the # mark is also applied to values with weak assignment arguments from other sources, if grouped together. An asterisk after the A means that a comment of some importance may be available in the original.
  • (B) National Nuclear Data Center, Brookhaven National Laboratory, information extracted from the NuDat 2.1 database. (Retrieved Sept. 2005, from the code of the popup boxes).
  • (C) David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes. — The CRC uses rounded numbers with implied uncertainties, where this concurs with the range of another source it is treated as exactly equal in this comparison.
  • (D) More specific level data from reference B's Levels and Gammas database.
  • (E) Same as B but excitation energy replaced with that from D.
  Z   N refs symbol   half-life                   spin              excitation energy
  2   1 ABC |He-3    |STABLE                     |1/2+
  2   2 ABC |He-4    |STABLE                     |0+
  2   3 A   |He-5    |700(30)E-24 s              |3/2-
  2   3 BC  |He-5    |[0.60(2) MeV]              |3/2-
  2   4 ABC |He-6    |806.7(15) ms               |0+
  2   5 A   |He-7    |2.9(5)E-21 s [159(28) keV] |(3/2)-
  2   5 BC  |He-7    |[0.15(2) MeV]              |(3/2)-
  2   6 ABC |He-8    |119.0(15) ms               |0+
  2   7 A   |He-9    |7(4)E-21 s [100(60) keV]   |1/2(-#)
  2   7 B   |He-9    |[65(37) keV]               |(1/2-)
  2   7 C   |He-9    |[0.10(6) MeV]              |(1/2-)
  2   8 A   |He-10   |2.7(18)E-21 s              |0+
  2   8 B   |He-10   |[0.17(11) MeV]             |0+
  2   8 C   |He-10   |[0.3(2) MeV]               |0+

Femto 15:43, 19 November 2005 (UTC)

Talk[edit]


From the description of helium-8:

Produced from 9He, decomposes to 7Li through beta decay then emits a delayed neutron.

Strictly speaking, doesn't it decompose first to 8Li through the beta decay, and then to 7Li by emitting the delayed neutron? —The preceding unsigned comment was added by 144.136.191.193 (talkcontribs) .

Seems to make sense. Just be bold and reword it. Femto 11:34, 29 July 2006 (UTC)

5He[edit]

The article makes it sound as though 5He was particle-bound. Actually, the half-life is on the order of c/x, where x is the size of the nucleus, so I think it's not particle-bound. IMO the article should make a clearer distinction between particle-bound and particle-unbound nuclei.--76.93.42.50 (talk) 21:00, 29 May 2008 (UTC)

Halo nuclei[edit]

Are the halo nuclei of 6He and 8He the reason they have relatively long half-lives, compared to the other unstable isotopes of helium? XinaNicole (talk) 23:54, 29 May 2011 (UTC)

Diproton[edit]

Helium-2 is a hypothetical isotope of helium which according to theoretical calculations would have existed if the strong force had been 2% greater. This atom would have two protons without any neutrons. Would 2He be a stable isotope, or would it beta-decay to 2H in such a hypothetical universe? And if it were stable, does that mean 2H would beta-decay to 2He, since generally only a single nuclide of a given atomic mass is stable? XinaNicole (talk) 02:19, 8 June 2011 (UTC)

Good questions, which we might start to answer if we could look up the source of this statement. I'll put a citation-needed tag on it. Dirac66 (talk) 01:38, 13 June 2011 (UTC)
This paper indicates that 2He would beta-decay to 2H with an unknown half-life. It also argues that very little 2He would be produced during Big Bang Nucleosynthesis, and thus that universe would have a very similar primordial makeup, but that stellar nucleosynthesis would proceed quite differently, with the first step being 21H -> 2He, followed by decay to 2H and then further fusion, but with 3He not being burned and instead building up in the core. He argues that, at the end of the hydrogen-burning phase, you'd have about 75% 3He and 25% 4He, followed by a 3He-burning phase and then a 4He burning phase! XinaNicole (talk) 10:50, 16 June 2011 (UTC)
An interesting paper in counterfactual physics (like counterfactual history :-)). Your free link does not give the source journal, but a Google search finds R.A.W. Bradford, J. Astrophys. Astr. (2009) 30, 119-131. It describes this hypothetical diproton state as "bound", meaning that the two protons would not immediately (10-23 s) separate due to coulomb repulsion as they would in the real world. However in Sec. 4 he considers the much slower weak (beta) decay, mentioning a possible time of the order of a year. So if this were correct, He-2 could exist for a reasonable time but would beta-decay. We still need the source of the calculations which give this result; possibly it is in one of Bradford's references.
Perhaps we can mention and link to Bradford's paper in the article. After the sentence you have quoted, we could add something like "Bradford [ref] has considered the hypothetical effect of this isotope on Big Bang and stellar nucleosynthesis." Dirac66 (talk) 02:15, 17 June 2011 (UTC)
2He has a very lopsided(!) ratio of protons to neutrons for such a light element, so it would most likely decay to 2H in a hypothetical universe where helium-2 is bound. Double sharp (talk) 06:28, 24 October 2012 (UTC)

Diproton in table[edit]

Should 2He (diproton) be included in the table of isotopes? Whoop whoop pull up Bitching Betty | Averted crashes 13:56, 27 July 2011 (UTC)

I would say no because it is still hypothetical. If its existence is ever confirmed then yes. Dirac66 (talk) 14:02, 27 July 2011 (UTC)
No, because it does not exist, and cannot, according to current theory. Plasmic Physics (talk) 14:03, 27 July 2011 (UTC)
Thank you, but then why is it included in the table of nuclides? Whoop whoop pull up Bitching Betty | Averted crashes 14:14, 27 July 2011 (UTC)
It shouldn't be there either, I don't know when it got in there, but it should go. Plasmic Physics (talk) 14:19, 27 July 2011 (UTC)
I agree that it should go, and I have continued this discussion at Talk:Table of nuclides#Remove He-2 (diproton)?. Dirac66 (talk) 15:32, 27 July 2011 (UTC)

Improbably short half-life for He-2[edit]

The intro now claims (since 19 October 2011) that He-2 has a half-life of 3x10-27 sec. Where does this number come from, please? I will mark it "citation needed".

Such a short half-life would seem to violate the speed limit of the universe. The time to separate two protons by a nuclear diameter of 10-15m cannot be less than 10-15m / c = 3 x 10-24s, so the claimed half-life implies that the protons are separating at 1000 times the speed of light.

Also there is a measurement problem here. Extremely short half-lives cannot be measured directly, but are deduced from the width of some resonance. Here the width would be ħ / 10-27s = 107 J = 1 TeV. Real measured widths are much smaller than that.

If these simple arguments are incorrect for some reason, we need to see the evidence.

Also in the section on He-2, the last two paragraphs are not properly referenced. One cannot just say that "The best evidence of He-2 was found in 2008 at the Istituto Nazionale di Fisica Nucleare, in Italy." We need a journal reference with author names, journal title with volume and pages and article title, and if possible an on-line link. Same for the Japanese and Russian work in the next paragraph. Does the 3x10-27s value come from one of these papers?? I don't know and I can't check if you don't tell me where the papers are. More "citation needed" tags. Dirac66 (talk) 14:37, 19 December 2011 (UTC)

P.S. Neither the Nubase nor the Nudat databases list a value for He-2. Dirac66 (talk) 21:48, 24 December 2011 (UTC)
I have now added a citation for the description of the Italian experiment. The information was hiding at Talk:Diproton. It says nothing about a half-live value or estimate. Dirac66 (talk) 15:10, 3 January 2012 (UTC)

He-2 decay to H-2 is also dubious and unsourced[edit]

Today 2H was added to the table as a supposed "daughter isotope" of 2He, as well as 2 1H which was already in the table. However if 2He to 2H really occurred, it would be a beta-plus decay (positron emission). This is difficult to believe since beta decay is a weak interaction which results in half-lives much, much longer than the 3 x 10-27 s claimed by the table for 2He. The two other beta-decay nuclei in the table are examples: 807 ms for 6He and 119 ms for 8He, compared to half-lives near 10-21 s for the neutron-emitting nuclei 5He, 7He, 9He and 10He. If 2He falls apart into two protons in 3 x 10-27 s (or even 10-21 s), it does not have time to beta-decay.

Once again we need sources for 2He, which is not listed in the Nubase or Nudat sources at the end of the article. I plan to just delete 2He from the table if sources are not provided soon. Dirac66 (talk) 20:00, 2 January 2012 (UTC)

The decay of 2He to 2H is the second step of the proton-proton chain reaction and is the rate-limiting step (the vast majority of the time it simply decays back into two 1H nuclei. Whoop whoop pull up Bitching Betty | Averted crashes 20:43, 3 January 2012 (UTC)
Hm - perhaps the claims about 2
2
He
come from the astrophysics literature. The p-p chain reaction article describes the first step as 1
1
H
 + 1
1
H
 → 2
1
D
 + e+ + ν
e
 + 0.42 MeV. I presume you mean that this occurs as two steps with the formation of 2
2
He
followed by positron emission.
I agree that the p-p chain is well established and can serve as evidence for positron emission. However I am not convinced that the system of two protons which emits the positron should be classified as a single 2
2
He
(or diproton), which would require that it have a potential energy minimum deep enough to form a bound state. Is there evidence that this is so? If the potential energy curve of two protons is in fact repulsive, then the equation should be written as a single step, as it is now in the p-p chain article. We still need a reliable source to settle this question. If the answer is complex, it may be better to quote the exact words of a source document.
Also even if we can document astrophysical evidence for the existence of 2
2
He
as a positron emitter, it should not be in the same table as the other isotopes for which the data is based on nuclear physics experiments and listed in NUBASE.

────────────────────────────────────────────────────────────────────────────────────────────────────The source is Giovanni Raciti, et. al in Physical Review Letters, 16 May 2008. It is not the astrophysical decay of the diproton (which incidentally might happen far faster than it takes the protons to separate by any distance, since they never do, inasmuch as one proton turns to a neutron by emitting a W which itself decays before it has gone even 0.1 fm). Instead, the Italians used a beam of neon-20 ions against beryllium foil. Some neon nuclei were stripped of two neutrons to Ne-18, which exited the foil and impacted lead foil. The collision excited Ne-18 nucleus into a instability. One of the decay modes for excited Ne-18 is double proton emission plus O-16. These two protons don't come out randomly, but in a single lump in a single direction-- in other words, bound together for a (very very) short time. From the angle between the two product protons after their agglomerate He-2 does break down, you can tell how long it must have held together. That was the number these guys got. SBHarris 06:00, 4 January 2012 (UTC)

Yes, this is the source for the Italian experiment described in the diproton section of the article. I found it yesterday from a link in Talk:Diproton and inserted both the Science News Update and the Physical Review Letter as references. It answers some of the above questions but not all.
First the PRL letter of Raciti et al. speaks of a "pair of protons, correlated in a quasibound 1S configuration." To be true to the reference we should use this description rather than presenting 2He as a nuclide like any other.
The PRL does NOT mention 3 x 10-27 s or indeed any value for the half-life. The Science News Update just says "much less than a billionth of a second", which is hardly helpful. Perhaps the "number these guys got" is in another of their publications? Or somebody's comment on their work? I think it is important to track down the source and check the argument made and the exact wording of the claim made. It is after all an extraordinary claim, 104 times faster than the next fastest nuclide (7H) so we should be certain it is correct and add any necessary nuances before inserting it.
Positron emission is a separate issue. As Whoop whoop pull up points out, it is part of the p-p chain and there is much astrophysical evidence for that. I erred in saying that 2He "does not have time to beta-decay". As you point out, an individual beta-decay event can be very rapid. The very small probability accounts for the much longer half-life of beta decays. Dirac66 (talk) 16:31, 4 January 2012 (UTC)

Who the #&@% is "Bradford"[edit]

Under the subtitle "Helium-2 (diproton)," the contributor suddenly introduces the name “Bradford” - as if we should all know who he is. Bradford is not a ‘Newton’ or an ‘Einstein.’ If he is not previously motioned, than his credentials should be stated to give validity to the article. At the very least, his full name (or initials) should precede his surname - try searching “Bradford” in the ‘search box.’ Manixx2a (talk) 23:46, 3 July 2012 (UTC)

At the end of the sentence there is a little [5] leading to a footnote which gives the author's initials (R.A.W. Bradford), and the article publication details (journal, volume, date, pages and title). Try Googling R.A.W. Bradford + astrophysics. Dirac66 (talk) 01:34, 4 July 2012 (UTC)

possible source for diproton[edit]

http://hal.archives-ouvertes.fr/docs/00/17/56/14/PDF/rpp.pdf Two-proton radioactivity - Bertram Blank ‡ and Marek P loszajczak †

Other is from RIKEN (?): http://fy.chalmers.se/~f2bmz/papers/korsheninnikov_2003_7h.pdf doi:10.1103/PhysRevLett.90.082501 p 2: "corresponds to our expectation that the two protons from the reaction p ( 8He; pp ) 7H can undergo final state interaction being emitted as a virtual singlet state 2He. This method was used in the study of 5H in the reaction p ( 6He; pp ) 5H [1]. \n When detecting the two protons by the RIKEN telescope, we obtain kinematically complete information about these two protons and, due to energy and momentum conservation in the reaction p (8 He; pp ) 7H, we can unambiguously reconstruct a mass of the residual system 7H. Also, we detected tritons and neutrons from the breakup of 7H using a downstream detection system consisting of a dipole magnet and plastic scintillators. This part of setup was the same as in our previous experiment described in Ref. [7]." `a5b (talk) 00:52, 19 July 2013 (UTC)