Talk:Neutron/Archive 3

Archive 1

Archive 2

Archive 3

Archive 4

GA Review

This review is transcluded from Talk:Neutron/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: StringTheory11 (talk · contribs) 04:46, 14 June 2012 (UTC)

I will review this article. StringTheory¹¹ 04:46, 14 June 2012 (UTC)

I am sorry, but I will have to quick-fail this article due to a SEVERE lack of sources and bad prose. I feel that I have to downgrade this article to a C, which I have done. StringTheory¹¹ 18:01, 17 June 2012 (UTC)

GA review – see WP:WIAGA for criteria

1. Is it reasonably well written?

   A. Prose quality:

   B. MoS compliance for lead, layout, words to watch, fiction, and lists:

2. Is it factually accurate and verifiable?

   A. References to sources:

   B. Citation of reliable sources where necessary:

   C. No original research:

3. Is it broad in its coverage?

   A. Major aspects:

   B. Focused:

4. Is it neutral?

   Fair representation without bias:

5. Is it stable?

   No edit wars, etc:

   Requesting semi-protection due to vandalism

6. Does it contain images to illustrate the topic?

   A. Images are copyright tagged, and non-free images have fair use rationales:

   B. Images are provided where possible and appropriate, with suitable captions:

7. Overall:

   Pass or Fail:

A few preliminary points to work on:

• There is a citation needed in the lead. This will need to be fixed.

• The references in the "further reading" section are not complete.

• Refs 1, 2, 8, 10-13, and 17 need to be more than bare URLs.

• Many refs need access dates.

• This article has many unreferenced paragraphs. I am of the opinion that every paragraph should have at least one reference before an article is a GA.

• I would rename "sources" to "natural sources", and move all artificial source info into "production". Also, the section needs to be expanded.
• Many subsections in "intrinsic properties" are too short to comfortably be sections. I believe that if a section only has one paragraph, it is not worthy of a section. Either expand these or merge then with other sections.
• "Neutron compounds" should be a subsection of "intrinsic properties".

More to come later. StringTheory¹¹ 04:21, 16 June 2012 (UTC)

CPT violation

I would suggest to either remove or rephrase the sentences

The fractional difference in the masses of the neutron and antineutron is (9±6)×10⁻⁵. Since the difference is only about two standard deviations away from zero, this does not give any convincing evidence of CPT-violation.

The reason is, that I find it somewhat missleading for the non-expert to read this value of (9±6)×10⁻⁵. If one is not familliar with the way of how confidence intervalls are build what a standart deviation is and does not read the lengthy article linked to in the next sentence this gives a wrong impression. It would maybe be helpful to write something like, that this does not show that this value is non-zero and hence does not allow to conclude that CPT symmetry is absent. Regards, Falktan (talk) 20:40, 19 June 2012 (UTC)

References

Interactions

It says one of the interactions is Electromagnetic, but it's neutral and not affected by the electromagnetic force. It's composed of quarks that are, but it's a neutral particle. ScienceApe (talk) 19:44, 20 June 2012 (UTC)

I think thats ok: The neutron has a magnetic dipole moment and hence interacts with magnetic fields. Regards, Falktan (talk) 12:01, 21 June 2012 (UTC)

What does that mean? ScienceApe (talk) 16:44, 21 June 2012 (UTC)

It means that each neutron acts like a little magnet. Put it in an inhomogeneous magnetic field (one that has a gradient) and it will experience a force. That's an electromagentic interaction. SBHarris 20:34, 21 June 2012 (UTC)

So then by implication it should be possible to collimate neutrons into a beam correct? ScienceApe (talk) 20:28, 22 June 2012 (UTC)

In theory, yes. [1] It's been difficult in practice since the magnetic moment is so small. SBHarris 20:33, 22 June 2012 (UTC)

Neutron lifetime

The neutron lifetime should be updated as it was lowered by the Particle Data Group to 880.1 s. see: http://pdg.lbl.gov/2012/listings/rpp2012-list-n.pdf — Preceding unsigned comment added by 138.246.2.58 (talk) 10:06, 21 March 2013 (UTC)

It should also be mentioned that the two main methods for measuring neutron lifetime give apparently consistently inconsistent results, the current best results for the "beam" method being 887.7 ± 2.3 s, see http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.222501 --Ørjan (talk) 05:46, 3 December 2013 (UTC)

That's a ever-so-slightly eye-raising for physicists in the field, but it's certainly not much cause for a concern on Wikipedia. 880.1 ± 1.1s and 887.7 ± 2.3 s fall within about 2.2σ of each other. Headbomb {talk / contribs / physics / books} 06:01, 3 December 2013 (UTC)

Oh I see, you meant beam lifetime vs bottle lifetime. Yeah something could be mentioned about that I supposed. Headbomb {talk / contribs / physics / books} 06:01, 3 December 2013 (UTC)

How does the quark structure model quantitatively account for the neutron lifetime?--188.26.22.131 (talk) 10:31, 3 December 2013 (UTC)

For something "ever-so-slightly eye-raising for physicists in the field", the paragraph in PDG sounds rather desperate. They "once again call upon experimenters to clear this up" and they are clearly unhappy with not having been able to quote a satisfactory interval since 2006. If you are happy to quote "just under 15 minutes", the problem goes away of course, but you cannot then quote "881.5±1.5 s" in brackets as if the 1.5s were just a regular standard deviation. The value is given with the rather unusual qualification of "we can think of nothing better to do" and "Note that the error includes a scale factor of 2.7. This is a jump of 4.2 old (and 2.8 new) standard deviations. This state of affairs is a particularly unhappy one, because the value is so important."

Under "mean life time", it should be noted that "the state of affair is a particulalry unhappy one" because experimenters for close to a decade haven't been able to decide whether the lifetime is about 880 or about 885 seconds. --dab (𒁳) 12:03, 18 January 2014 (UTC)

Magnetic field influence

The article should mention if there is some influence on neutron lifetime by magnetic fields. (a neutron beam in magnetic field for instance)--193.231.19.53 (talk) 10:11, 7 January 2014 (UTC)

Thermal Neutron

The comment:

"thermal neutrons have a much larger effective cross-section than faster neutrons"

does not appear to be correct. This is insinuating that the cross-section is a property of the neutron. The cross-section is a property of the material whereas the effective relative velocity between the neutron and the target nucleus changes the cross-section. This is most easily reflected in the 1/v dependence, save for nuclear resonances. — Preceding unsigned comment added by Jesse.johns (talk • contribs) 00:51, 30 November 2013 (UTC)

The cross section is a property of the SYSTEM of particles, not either alone. I will fix it. SBHarris 06:45, 3 December 2013 (UTC)

De-(un)-archiving

Arhive 2 of this talk page has not many valid reasons to exist, most of it is relevant to present discussions, it should be unarchived, but I don`t know how.--188.26.22.131 (talk) 10:02, 3 December 2013 (UTC)

All these discussions are stale and several years old. If you have specific comments, feel free to unarchive specific threads (like I did below), but the bulk of these discussions should stay archived. Headbomb {talk / contribs / physics / books} 13:45, 3 December 2013 (UTC)

Magnetic moment

Un-archived from /Archive 2 on 3 December 2013.

How is explained the nonzero magnetic moment of the neutron, unusual for a electrically neutral particule?--MagnInd (talk) 10:24, 6 August 2010 (UTC)

Neutrons are not fundamental particles. They have electrically charged quarks inside of them. Dauto (talk) 15:25, 30 August 2011 (UTC)

How about Rutherford model? How do the models account quantitatively for the observed magnetic moment of the neutron in comparison one to the other?--188.26.22.131 (talk) 10:14, 3 December 2013 (UTC)

Is there any published comparative quantitative explanation of the magnetic moment by quark model and Rutherford model to decide which one is best? Or at least just of a quantitative account of the magnetic moment by the quark structure model?

I'll rephrase my edit to my first edit, whithout the claim of experimental support for Rutherford model, to which I understanding user Headbomb objects.--188.26.22.131 (talk) 10:29, 3 December 2013 (UTC)

This material simply is unfit for Wikipedia. First you say Rutherford's model is derelict, then follow up with a "well the jury is still out on this". Rutherford's guess was made at a time when no one knew of quarks, he did the best with what he had around at the time. But the jury has been in on this for 50+ years, and what accounts for the neutron's magnetic moment are the intrinsic magnetic moment of quarks. See doi:10.1007/BF02760010 and references therein. Headbomb {talk / contribs / physics / books} 13:31, 4 December 2013 (UTC)

I haven't said is derelict, just considered so. A more cautious phrasing is needed. The issue in discussion here is not wether or not neutron is made of quarks, but the explanatory power of structure models formulated over the time since the prediction and discovery of the neutron.--188.26.22.131 (talk) 10:55, 16 December 2013 (UTC)

text/reply brought from Wikiproject Physics:

Has anyone any objection to the above proposal of a more cautious wording?--193.231.19.53 (talk) 10:00, 17 December 2013 (UTC)

Yes. The Rutherford model explains nothing because it is wrong. Headbomb {talk / contribs / physics / books} 15:08, 17 December 2013 (UTC)

end of brought text — Preceding unsigned comment added by 188.26.22.131 (talk) 14:18, 20 December 2013 (UTC)

I have noticed this discussion and also the article proton spin crisis which I understand is an unsolved puzzling problem. Is there an article that tries to treat proton spin crisis based on quark structure of the proton?

As a remark, it appears from the Nuovo Cimento source that the quark structure model create more problems than it solves. It would interesting to see if there is a calculation of magnetic moment of the neutron based on the Rutherford model. If there is, a comparison between the models in regard to explanatory power would be useful.--193.231.19.53 (talk) 09:51, 5 December 2013 (UTC)

Only a quantitative comparative test of the explanatory power of two structure models would allow the categorical conclusion that neutron consist of quarks, if the quark structure has a better quantitative explanatory power. It seems that a comparative test of the two models has not been done. Therefore both structure models should be presented in the article.--193.231.19.53 (talk) 11:04, 10 December 2013 (UTC)

No. That neutrons are made of quarks has been established since the 1960s. Please stop wasting editor's time. Headbomb {talk / contribs / physics / books} 14:23, 10 December 2013 (UTC)

This is not waste of time, it is a legitimate aspect of scientific investigation procedure, by another name an application of the scientific method. The claim that neutrons are made of quarks has been established since the 1960s has little scientific support from the point of view of exaplanatory power. I have asked you if you aware of data regarding magnetic moment of quarks. You have rather dismissed the issue on a rather superficial analysis, so the quantitative account of magnetic moment by quarks is not very clear. The statement about the explanatory power of the two models should in the article. A clarification is needed, in the 1960s hypotheses about quarks were formulated, not established categorically.--193.231.19.53 (talk) 15:32, 10 December 2013 (UTC)

It is indeed a waste of time (see WP:CHEESE). The existence of quarks (and likewise that neutrons are made of quarks) has been established beyond a shadow of doubt since the late 1960s. Headbomb {talk / contribs / physics / books} 15:43, 10 December 2013 (UTC)

Comparing this discussion with WP:CHEESE is ridiculous.--193.231.19.53 (talk) 10:17, 17 December 2013 (UTC)

As stated above, the present discussion is not about wether or not neutron is made of quarks.--188.26.22.131 (talk) 10:58, 16 December 2013 (UTC)

text brought from Wikiproject Physics:

Rutherford's article from 1920 concerning prediction of a neutron has been brought to my attention long before the recent mention of someone like Santilli by Headbomb. If someone like Santilli considers worth buiding upon Rutherford's hypothesis, that is an entirely different aspect.--193.231.19.53 (talk) 10:09, 17 December 2013 (UTC)

There are a fair number of arguments that show that a neutron cannot be made of a proton+electron. Consider the following:

1. Decay of a neutron yields a proton, electron, and an electron anti-neutrino. Now, maybe you could argue that the protron and electron are somehow "stuck together" in the neutron, but surely you agree that nothing can possibly confine the neutrino to the neutron? Remember, neutrinos are perfectly capable of penetrating light years of matter.
2. Even the notion that a proton and electron could stick together is flakey, because of the Heisenberg uncertainty principle. It is quite simply inconceivable that an electron can be confined to the volume of a neutron.
3. The electron is not subject to the strong force, so it can not be made to "stick" to the proton. Electromagnetic associations of protons and electrons are known as "hydrogen atoms".
4. These arguments show that the electron and anti-neutrino could not have pre-existed as neutron constituents. The only explanation that makes sense is that the electron and the anti-neutrino were created during the decay event. Do you need more proof? I got more proof.

Stigmatella aurantiaca (talk) 00:00, 18 December 2013 (UTC)

As for arguments relating to the magnetic moment, see SSM Wong (1998), "Magnetic Dipole Moment of the Baryon Octet", Introductory Nuclear Physics, § 2.8, pp. 48ff, ISBN 978-0471239734 (or any other intro to nuclear physics textbook, really).Headbomb {talk / contribs / physics / books} 03:10, 18 December 2013 (UTC)

Wong ref--193.231.19.53 (talk) 10:32, 13 May 2014 (UTC)

It turns out that the quark model cannot account for neutron magnetic moment, just for the ratio of magnetic moments of proton and neutron.--193.231.19.53 (talk) 11:51, 13 May 2014 (UTC)

Magnetic moment of an elementary neutron

I am puzzled by the discussion of the non-zero magnetic moment, which considers only the Rutherford model of the 1920s and the quark model of the 1960s which is now accepted. Historically there was a 30-year period, roughly 1934-1964, when the neutron was considered to be an elementary particle, and known to have spin 1/2 which excluded the Rutherford model. Quarks of course had not yet been thought of. So my question is: if a neutral elementary particle cannot have a magnetic moment, then how was the magnetic moment of the neutron explained during this period?? Dirac66 (talk) 02:36, 16 January 2014 (UTC)

Perhaps it wasn't explained at all, even the quarks at present have a weak explanatory power as can be seen from the mentioned source fron Novo Cimento. Or perhaps the Rutherford model has not been fully replaced until the conceptualisation of quarks.--188.26.22.131 (talk) 11:02, 27 January 2014 (UTC)

The neutron and proton magnetic moments to 3 sig digits, including the odd fact that the neutron moment is in the wrong direction from that of the proton (as though the neutron were a negative particle) was measured by Alvarez in 1940. And indeed he can't explain it. He simply says that present theory can't account for the magnetic properties of these particles. [2]

Although oddly, once the moments were known, theory could account for the moment of the deuteron, which is just the arithmetic sum of moments of the proton and neutron, both spinning in the same direction.

It would have been interesting if Alvarez had had the imagination to think of a neutron as a particle with a positive core balancing a negative "skin" so that a spin in the direction of the proton gave an opposite magnetic moment. Something fishy is going on inside the neutron, as Feynman says in his 1964 lectures. Later scattering experiments found just that (negative skin, positive core). And of course if you think of everything as particles, this implies negative and positive particles in neutron and proton.

BTW, although it is true that one early success of the quark theory was to predict the ratio of proton to neutron moments as -2/3 (which they very nearly are), there are many different quark models that give both proton and neutron moments correctly to 3 figures, and moments of heavier baryons as well. But all these models are a bit ad hoc, as you have to assume some physical model like harmonically oscillating quarks, or a bag full of quarks with complete freedom inside the bag and none outside. So people use the known moments to probe and deduce quark confinement and potential models, since there is a lot of freedom there. Depending on what you decide, you can predict any moment you like. SBHarris 05:13, 21 August 2014 (UTC)

I've just noticed a 1934 paper by Igor Tamm in Nature that discusses the magnetic moment of the newly discovered neutron : [3]--193.231.19.53 (talk) 12:20, 6 November 2014 (UTC)

Neutron mass measurement

The article should present the methods for measuring the mass of the neutron and the (tacit) assumptions (if there are) involved in measuring.--5.15.206.141 (talk) 12:33, 3 January 2014 (UTC)

Well, today's edit by ‎188.26.22.131 tells us that The mass of a neutron cannot be directly determined by mass spectrometry due to lack of electric charge. So that's one way not to measure the mass. Now could someone please explain how it is measured, since the infobox does give a value to many significant figures? Dirac66 (talk) 03:13, 2 August 2014 (UTC)

Yeah, It is not only a way to measure the mass, it seems inapplicable on other grounds: mass spectroscopy seem to be a term used for measuring the mass of ionized atoms, not charged particles generally (although, ander a different name, the technique can be applied to charged particles). My point is that as phrased, it is not encyclopaedic, and I'd prefer to see the addition removed.

The earliest measurement of the mass of the neutron appears to have been done by Chadwick, by observing energies of reactants and products in a nuclear reaction (S. B. Patel (1991). Nuclear Physics: An introduction. p. 125.). While this probably belongs in the historically oriented section § Discovery, it is clear that it is possible to measure the mass by analysis of interactions in which a free neutron is involved, through conservation of energy and momentum. Hopefully, someone with access to suitable material can add how this measurement is done in modern times. I expect, for example, that analysis of the observable decay products of cold neutrons would allow a fairly direct calculation, even given that the antineutrino escapes without measurement. (The total momentum starts as essentially zero, so the neutrino's momentum can be determined, hence its energy, so total initial mass–energy can be determined, since the electron and proton both have accurately known mass and their momenta can be measured directly.) —Quondum 14:49, 2 August 2014 (UTC)

The best modern values simply measure the wavelength of the capture gamma when cold neutrons are absorbed to protons in protium (light hydrogen) to make deuterium. It's a very sharp peak, since there is only one gamma emitted and this nucleus has no excited states. So you measure the wavelength of the gamma by crystal spectroscopy, and that gives its energy. You know the mass of the proton and deuteron by mass spectroscopy, and subtracting energy of gamma and proton from deuterium gives mass of neutron as residuum. There's a tiny correction for recoil kinetic energy of the D nucleus, which must be added back in. SBHarris 22:41, 19 August 2014 (UTC)

Neat. Would you be able to add this in? Even if it is unsourced, this description is an improvement on a negative statement about measurement of mass. —Quondum 23:30, 19 August 2014 (UTC)

Okay, I put it in. Byrne (2011) give values that are slightly more precise than 2011 CODATA for the mass in u, but slightly less precise than the CODATA for the value in MeV. It may be that since Bryne was doing his manuscript, CODATA came up with a slightly better u to MeV conversion, which is what limits the number of sig digits in Byrne's neutron mass in MeV. SBHarris 02:10, 21 August 2014 (UTC)

Thanks. That filled a definite hole in the article. —Quondum 03:06, 21 August 2014 (UTC)

I think a formula with the calculation of the mass of the neutron from the mentioned data should be put in article.--5.15.37.250 (talk) 21:17, 25 August 2014 (UTC)

Synthesis from proton and electron

What conditions are necessary for the occurence of synthesis of free neutron from proton and electron?--188.26.22.131 (talk) 15:41, 7 February 2014 (UTC)

Radius

What methods are there for determining the radius of a neutron?--188.26.22.131 (talk) 12:48, 28 March 2014 (UTC)

Per wp:talk page guidelines, please take this to wp:Reference desk/Science. - DVdm (talk) 12:51, 28 March 2014 (UTC)

But perhaps this question should be considered as a suggestion for addition of content to the article. A more correct phrasing would be Can we add a section to the article to consider what methods there are for determining the radius of a neutron? Dirac66 (talk) 15:45, 28 March 2014 (UTC)

Or, equivalently, should the article give some estimate of the effective size of the neutron? (e.g. effective density in a nucleus, average internal quark separation, etc.) Intuitively, there might be various measures of this, since it is not a point particle like an electron. Yet, at a glance, the article seems to make no mention of any size-related figure. —Quondum 17:46, 28 March 2014 (UTC)

Yes, I think the article should, and I'll try to spare some time to do that soon. Dan Gluck (talk) 14:40, 20 June 2014 (UTC)

Stability of neutrons in nuclei - wrong explanation in article?

I am not sure I agree with the brief explanation of why neutrons do not decay within nuclei. As was once explained to me, neutrons within nuclei do not decay to protons because of the Pauli exclusion principle - any newly created proton has no where to go, since all the spin states for protons are filled within stable nuclei. (Could go to a higher energy state, I suppose, if there was additional energy to allow it to be there.) Now that I think about it, the argument in the article suggests that all matter is unstable, since it suggests neutrons within nuclei would all rapidly decay to make all nuclei unstable... I would change the article, but its a little out of my field. Bdushaw (talk) 07:45, 14 August 2014 (UTC)

The explanation in the article is, in some sense, the same as yours, except that yours is stated in black and white. It is not a case of "has nowhere to go", but rather that it is energetically unfavourable. A slightly better, but still rather simplified picture is that if the decay were to occur, the new neutron proton would be in a "high pressure" environment. If the energy of decay is less than that needed to squeeze a new proton into the environment, it is energetically unfavourable. I think the article's use of "instability that would be acquired" is a poor choice of phrase, though. —Quondum 14:27, 14 August 2014 (UTC)

Which section are we discussing please? Bound neutron decay? Dirac66 (talk) 15:18, 14 August 2014 (UTC)

Yes, Neutron#Bound neutron decay is what I presumed was being referred to, being the closest thing I could find matching the description. The sentence fragment "the energetic instability of a single neutron to beta decay is balanced against the instability that would be acquired by the nucleus as a whole if an additional proton were to appear by beta decay" uses the term "energetic instability", which is not something with an obvious definition (to me). —Quondum 16:25, 14 August 2014 (UTC)

That's the section and phrasing that I was asking about. Surely the Pauli exclusion principle is relevant here? This property trumps the energetics of the situation, seems to me - there are no energy states within the nucleus that can accept another proton (usually, but not always). The explanation I heard was straight from the mouth of a professor of physics at UC Irvine. To back up a bit, a common question, and the one that I asked was, "how come the free neutron has a half life of 14 min. (or whatever), but a bound neutron is stable?" That was quite a while ago, but I don't think nuclear physics has changed that much since then. Bdushaw (talk) 20:45, 14 August 2014 (UTC)

I have looked into the question some more, and there seems to be a surprising lack of clarity on the question. On the one hand, the nuclear shell model - which I believe models the nuclei with protons and neutrons in quantum energy states - relies on the Pauli exclusion principle to lend stability to protons/neutrons in nuclei. On the other hand, other web pages make arguments based on energy alone - decay of a neutron bound within a nucleus to a proton requires more energy. At a more primitive level, one could model the whole nuclei by quarks and gluons, but I think that line of thinking is not necessary and doesn't help much. My intuition is still that any explanation must appeal to/or include the exclusion principle at some point - how can one avoid it? Web searches have not turned up a bullet proof reference on this issue; it may be a matter of finding the right nuclear physics book that has this discussion (I have Feshbach and de Shalit, but it is down in the basement somewhere). Bdushaw (talk) 18:47, 19 August 2014 (UTC)

Good explanations might be rare. Your two descriptions are complementary rather than mutually exclusive: the Pauli exclusion principle is the reason that the only available proton states have higher energy. Electrostatic repulsion also plays a part. This then leads to the result that in many nuclei, decay of a neutron can only proceed with an input of energy. —Quondum 21:13, 19 August 2014 (UTC)

Of course bound neutron decay does occur as beta-decay in some nuclei, ¹⁴C for example. I think a correct statement would be that a necessary condition for the occurrence of beta-decay is the existence of an available proton state at lower energy than the highest occupied neutron state. This has more tendency to be true in neutron-rich isotopes. Dirac66 (talk) 01:42, 20 August 2014 (UTC)

And both types of beta decay can happen in a single isotope. Example: copper-64 has one unpaired proton, and one unpaired neutron, so its problem can be solved in either direction. And in fact in this particular nuclide (though not all nuclides with this situation) is almost equally likely to decay by turning a proton (61%) to a neutron (positron emission), as to go the other way (39% beta emission). It makes a nice illustration of how things can be on the "fence" due to double pairing-instability. SBHarris 02:47, 20 August 2014 (UTC)

I've had a go at rewriting this subsection according to these nice examples above. I also added a brief mention of proton decay in the subsection above. See what you make of it; do what you will... Thanks for the nice discussion. Bdushaw (talk) 19:33, 23 August 2014 (UTC)

Thanks for doing the rewrite. I think the bound neutron decay subsection is now pretty good, and only needs a few minor clarifications such as specifying that an available proton energy state must have lower energy than the initial neutron.

However the mention of proton decay is more seriously flawed, in that it seems to confuse proton decay with inverse beta decay (positron emission). Actually proton decay is not analogous to the neutron decay discussed here; instead it is a completely different process which may take place on enormously long time scales (10³⁴ years if at all), and does not even form neutrons which are the subject of this article. However Sbharris above did not actually refer to proton decay, but rather to positron emission, which is energetically forbidden in free nuclei but takes place on normal (human-compatible) time scales in some nuclei, e.g. 110 minutes in fluorine-18. Since this article is about neutrons, I think we should refer only to inverse beta decay (positron emission) by protons which is analogous to the beta decay of neutrons, and delete any mention of proton decay which has no analogy for free neutrons (because the neutrons disappear first by beta decay. I will make this change. Dirac66 (talk) 00:08, 24 August 2014 (UTC)

Feynman diagram is incorrect...

I've noted that the Feynman diagram is incorrect, since the antineutrino is traveling backward in time.... I think the direction of its arrow should be changed as the least confusing way to fix the problem. If the diagram is changed to correctly indicate a neutrino traveling backward in time it would likely confuse most people. Looking into the matter, this error was noted quite a few years ago with this particular diagram - there must be a correct one posted by now. I've had fun polishing various parts of this fine article, but I am tapering off now... See you later on wikipedia! Bdushaw (talk) 20:32, 24 August 2014 (UTC)

Two conventions exist, one where the outcome is explicitly labelled (ν_e, e⁻), the other where the only the basic fermion type is labelled (ν_e, e), and you get particle/antiparticle from the direction of the arrows. Both are valid ways to label things. Headbomb {talk / contribs / physics / books} 21:18, 24 August 2014 (UTC)

I understand, but I don't have to like it... :) Bdushaw (talk) 07:21, 29 August 2014 (UTC)

It's a tradeoff between expert convenience (who know that a fermion traveling backwards in time = antiparticle) and clarity to the layperson (who don't know that and could not make sense of such a diagram without running into some major WTFs). Experts can follow both conventions easily, layperson can only be reasonably expected to follow the second one. Headbomb {talk / contribs / physics / books} 15:12, 24 September 2014 (UTC)

It seems more like a conflation of the two than a tradeoff, like a double-negative. The direction of the arrow must be reversed to get the suggested tradeoff. This reminds me of someone who insisted that kilograms per cubic metre should be written kg/m⁻³. —Quondum 16:54, 24 September 2014 (UTC)

Nope. We don't get to create our own (and much worse) convention. This convention is both mainstream [e.g. http://ned.ipac.caltech.edu/level5/Cottingham/Cott1_7.html] and clear. Headbomb {talk / contribs / physics / books} 12:26, 25 September 2014 (UTC)

I see that Feynman used this notation in his QED: The Strange Theory of Light and Matter, and it has presumably stuck.^{revision: Feynman seemed to use the base particle plus arrow convention, not what is in the diagram in this article} It is easy for you to say that it is clear, but even Feynman diagram fails to make it clear. Perhaps you'd care to clarify the convention there? ("much worse": I've noticed that people tend to be biased towards what they are familiar with, so without more context, I cannot give that sentiment any weight.) —Quondum 15:22, 25 September 2014 (UTC)

The convention may be mainstream but it is certainly not clear to the general reader who is not familiar with things moving backwards in time, except in the movie Back to the Future. To a chemist, this diagram appears to say that the antineutrino is a reactant rather than a product. I understand from the above discussion that this is not true, so can someone please add a sentence to the image caption explaining the point? Dirac66 (talk) 00:55, 27 September 2014 (UTC)

It's worse than that: The arrow does not mean an antineutrino moving backwards in time, which any logically minded person would read into it; the arrow's orientation in time seems to indicate whether it is a "fermion" or an "anti-fermion" as seen in the forwards-time direction, regardless of the label on the arrow, and as senseless as such a classification is. Both conventions mentioned by Headbomb make perfect sense (basic type plus arrow, or explicit type without an arrow), but combining the two as in the diagram is a logical mess. —Quondum 03:30, 27 September 2014 (UTC)

I tend to agree. I suspect the problem lies with the perception that these diagrams are just nice ways to illustrate reactions. But they are really technical depictions of equations of interactions - the two uses are not really compatible. The situation may be hopeless. Bdushaw (talk) 07:29, 27 September 2014 (UTC)

I have a different perception: that the diagram conventions are generally perfectly rigorous, i.e. that a diagram corresponds directly to an equation. I think that problem comes in diverging from the rigour in a misguided attempt at supposedly making it more readily interpretable to the non-expert. —Quondum 15:42, 27 September 2014 (UTC)

Tweaked Introduction

I wandered off into the topics of nuclear astrophysics, etc. and then realized that this article was overly earth-centric, if you know what I mean. I've introduced nucleosynthesis in the introduction to emphasize that neutrons are not just something that happens on Earth/made by man. See how you like it. Bdushaw (talk) 07:21, 29 August 2014 (UTC)

The numerous articles having to do with this and a wide variety of similar topics are a bit of a mess, alas. Many of the articles ought to be combined, if you ask me, e.g., neutron capture nucleosynthesis, r-process, s-process all have separate articles. Similar with a wide variety of duplicating articles on nuclear reactions/processes/properties. There's a huge, thankless task... Bdushaw (talk) 07:21, 29 August 2014 (UTC)

Wikipedia is a huge thankless task. We rarely combine articles here, however, because there needs to be room for the thing to grow. If one article is about exactly the same subject as another, it's okay to combine, but s-process and r-process (both stellar processes) and capture-nucleosynthesis (quite often a reactor process) all have books written about them, and can easily support separate articles. Quite often you notice that you can combine shorter articles into a longer one, but if they are destined to grow and be spun off one day per the WP:SS process, such combining just ends up swimming upstream of our task here. For example, once upon a time a bunch of smaller articles about UV were stitched crudely together to make the monster Frankensteinian ultraviolet article. Great-- all that related info in the same place! But now it's too long and all those subarticles need spinning off again. So all that is like digging a hole, filling it up, digging it again, etc. Or like going into Afghanistan for the third time. Pick your metaphor. SBHarris 21:15, 6 September 2014 (UTC)

Discovery section

Just when I think I am out, they pull me back in... I keep trying to move on from this article, but I keep coming back to it. I contemplate a rewrite of the Discovery section, which I find could use some reorganization, clarification, and development. I don't think I understand the final sentence of that section on hyperfine spectra. So far what I've done seems to have been tolerated, at least, so I think I will proceed at some point. The neutron is at the center of that history of physics that I quite enjoy - a pretty stunning series of events between 1915 and 1945! Bdushaw (talk) 20:37, 4 September 2014 (UTC)

I've taken a first crack at reorganizing the section. Not at all content with where the situation is now, but it indicates what I have in mind. I am pausing to think about it a bit more and give you all a chance to comment. The next developments may be to cutback the subsection on the proton-electron model and develop the neutron-proton model subsection a bit more. I want to note somewhere that the energy/mass of a nucleus is less than the sum of the energy/mass of the individual nucleons, an obvious consequence of the stability of the nucleus and why the mass of a nucleon is slightly greater than one a.m.u. Bdushaw (talk) 18:59, 6 September 2014 (UTC)

I don't think the proton-electron model should be cut back. It is historically important to understand that the development of nuclear physics was slowed by the fact that physicists were on the wrong track in the 1920's, and I think this should stay in Wikipedia. It should not mislead anyone since it is clearly stated at the outset that the model was incorrect. But do go ahead and expand the correct neutron-proton as well, to show where the correct model came from.Dirac66 (talk) 21:16, 6 September 2014 (UTC)

I'm sure you're doing fine. Here's a cheer from an amateur bystander, anyway! --Ørjan (talk) 03:12, 7 September 2014 (UTC)

A bit more development today, but I may be done for the day. I'll tackle the proton-neutron model another day, if someone doesn't get there before me. The section may need a bit more on the actual experiments that Chadwick performed to prove the neutron. Bdushaw (talk) 20:02, 7 September 2014 (UTC)

It occurred to me that beta radiation was a key piece of information motivating the proton-electron model. Rutherford's 1920 paper has the quote, noted in the article, but he does not explicitly say beta particles. A nice reference supporting this notion would be nice; I don't know of one. It is obvious, really, that Rutherford was right, it was just that the electron was still a twinkle in the proton's eye, waiting to emerge via beta decay! Bdushaw (talk) 22:21, 7 September 2014 (UTC)

Yes, in the 1920's it seemed intuitively obvious that if an electron comes out of the nucleus, it must first exist inside the nucleus. It was only after the accumulation of evidence against this model, plus the observation of the neutron by Chadwick, that physicists were ready to accept that beta decay actually creates the electron.

Also, re the enormous energy of an electron confined to a nuclear volume, your edit summary says that it should be momentum. I disagree. An electron and a proton confined to a nuclear length L would both have momentum of the order of h/L. But the kinetic energy = p²/2m would be much larger for the electron because of its much smaller mass. Dirac66 (talk) 00:48, 8 September 2014 (UTC)

I think it should be specified what is the evidence against model and how the very large energy of an electron compared to that of a proton excludes the free electron from the nucleus? Some tacit assumptions must be clearly specified. Also, regardless of free electron being excluded from nuclei, the presence of a bound electron in a neutral double (neutron) as conceived by Rutherford has not been disproved. The neutron can be a nuclear particle in a similar way that does not exclude alphas from being nuclear particles.--82.137.15.208 (talk) 11:32, 13 September 2014 (UTC)

I agree with this sentiment. Simply stating that the kinetic energy is much larger than that of a proton confined to the same volume does not make it obvious that it cannot be confined; after all, the kinetic energy of the proton is not obviously a limiting factor for confinement to the reader. It might be useful if the kinetic energy of the electron could be shown to be significantly larger than, say, the mass difference between ³H and ³He, or something that shows more directly that the energy is larger than can be explained. —Quondum 17:46, 13 September 2014 (UTC)

Someone should check my math, but I get an electron kinetic energy of about 50000 MeV. R=1 fm, h-bar/R=0.7 eV-s/m; electron mass 0.5 MeV/c^2. Its that pesky c^2... We are getting into original research, however. Bdushaw (talk) 20:58, 13 September 2014 (UTC)

We are presumably into highly relativistic velocities, so the electron's energy is essentially independent of its rest mass: E = ħc/2R = 621 MeV 98.7 MeV. This is approaching the rest mass of the proton, and the (negative) binding energy would balance some of the added mass due to kinetic energy; thus the bound–pair "neutron" mass (assuming a radius of 1 fm) would be definitely under double the mass of the proton. Since this binding energy is not more than the original mass, we are not into true negative energies. So this is not a clincher for ruling out the proton–electron model, by my calcs. —Quondum 03:37, 14 September 2014 (UTC)

I'm certainly not an expert, but based on our discussions, this seems not correct. The uncertainty principle specifies momentum, and this momentum gives E=p^2/2m_e=ħ^2/2R^2 m_e, which is where I got 50 GeV. The point is that the nucleons and electrons have the same scale of momentum, but the tiny electron mass pushes the corresponding energy to huge numbers. Must depend on electron mass, somewhere. Presumably the Russian reference has this calculation, however; we need not/should not rely on original research. This is an encyclopedia not a publication or term paper - we don't have to prove these sorts if things, if references state them. Bdushaw (talk) 06:38, 14 September 2014 (UTC)

Poking around online a bit more, you are right that the problem is quickly relativistic. KE=sqrt(p^2c^2 + me^2 c^4) - mec^2. For deltaX= 0.1 nm, KE=0.96 eV, while for deltaX=10 fm, KE=9.4 MeV. However, the ground state of the electon has energy 13.6 eV - in atomic scale the electron can be trapped, while in the nuclear scale it cannot. I don't believe this UCSD physics problem solution set I am looking at is a valid wikipedia reference, however.... Bdushaw (talk) 07:15, 14 September 2014 (UTC)

To perhaps state the obvious, the issue seems to be that the kinetic energy of an electron confined to scales of the nucleus is large relative to the allowed energy states of the electron. I suppose it is impossible to construct a potential well of any design that would allow the electron to be confined to nuclear length scales. It is obviously possible for the massive nucleons to have energy states larger than their kinetic energy. Bdushaw (talk) 10:01, 14 September 2014 (UTC)

I was working from the formula you've given, and the Heisenberg uncertainty principle, σ_xσ_p ≥ 1/2ħ or p_x ≥ 1/2ħ/R, since standard deviation is a good proxy for whatever we mean by the radius and momentum in these formulae. I'll be a bit more rigorous here. Since the confinement is in three dimensions and each dimension contributes, the total momentum squared is p² = p_x² + p_y² + p_z² ≥ 3/4ħ²/R². Since we are relativistic, the rest energy m_ec² is tiny compared to the KE, and can be ignored. Which leads us to KE = √p²c² + m_e²c⁴ − m_ec² ≥ √3/4ħ²c²/R² + m_e²c⁴ − m_ec² ≈ √3/2⋅ħc/R. Using ħ = 6.58×10⁻¹⁶ eV⋅s and R = 1 fm, we get KE ≥ 171 MeV. Aside from a small factor, this is in agreement with a 10× scaling of your 10 fm, 9.4 MeV figure. The proton's charge radius is slightly under 1 fm, and with three quarks, we can see that bulk of the mass of a proton appears to be KE of the quarks; this is a clear example where low-mass particles are confined to the size of a proton. And since the proton–electron model does not necessarily assume the electron to be electrostatically confined, and the KE due to confinement could be provided by some near-range force as with the quarks, I do not think that it is valid to claim that simple energy considerations are a counter-argument to the model. If there is a subtler argument, it would have to be sourced, but for now we'll just have to remove the footnote. —Quondum 15:57, 14 September 2014 (UTC)

I think we are in agreement with the numbers and physical interpretation. The footnote came about in an attempt to describe how the uncertainty relation gives an energy from a given confinement, to avoid the error of implying that this uncertainty is space-energy, rather than space-momentum. It is clear the depths of the argument are more complicated than just "the energy is too large", and has also to do with what one assumes is the force that confines the electron and the energy of the resulting ground state. The argument seems to be well documented, but may be centered on quantum mechanics in the 1920s, without creative assumptions for exotic forces that might be able to confine the electron. I've not been able to find a suitable reference, and the two Russian papers mentioned in the article are not readily available. We have to be careful to avoid "original research" here which is verbotten on Wikipedia. Bdushaw (talk) 19:02, 14 September 2014 (UTC)

Attempted to correct the footnote, but I am not altogether satisfied with the situation. Bdushaw (talk) 19:27, 14 September 2014 (UTC)

I basically agree with Bdushaw here. The footnote is an attempt to clarify the reasoning of physicists in the late 1920's. Any discussion of quarks is an anachronism in this context.Dirac66 (talk) 19:39, 14 September 2014 (UTC)

Dirac66, I think the applicable term would be prochonism. My mention of quarks was intended as a retrospective argument to show that no argument based purely on the space–energy tradeoff would have been valid. I agree that we seem to have a mutual understanding, and that new forces would have been necessary to explain the confinement (but I don't think they'd've been averse to considering such). If there are arguments that were made at the time, it is clear we'll only be able to find these from the sources, because we cannot hope to infer what the reasoning might have been. The measurement of spin and of energy–momentum deficit in beta decay seem to me to be the first real evidence that might sink the proton–electron model. For what it's worth, the assertion seems to have been introduced in this revision. There was nothing in that edit to suggest that this was the crux of the Russians' argument and not OR; retaining even a diluted version of this statement seems problematic without verifying the references; the actual figures and argument given now are clearly OR. —Quondum 20:36, 14 September 2014 (UTC)

We've also not noted that these estimates of kinetic energy are much larger than the observed energies of beta rays emanating from the nucleus. I see that argument used here and there. Most of the references I've seen commenting on this argument make only vague statements about quantum mechanical objections, without anything specific. It is clear the argument is a standard problem for homework or quiz in a quantum physics class these days. I suppose I am in favor of retaining the argument, while keeping the tradition of being vague about the actual numbers and argument specifics. Happy to let others tweek the paragraph/footnote if they see a better way of writing it. Bdushaw (talk) 21:11, 14 September 2014 (UTC)

I note philosophically that there was obviously a great deal of confusion at the time, with some people knowing all about it, while others not so much. I think our discussion above is, curiously, a faint echo of that historical confusion. Attempting to write this wikipedia section based on the original sources will likely only lead to confusion. I've been contemplating Bohr's notion that conservation of energy had to be abandoned; Bohr should have known better, but who am I to say! Bdushaw (talk) 21:21, 14 September 2014 (UTC)

Just when I had about given up, I find this reference: [4]

I guess we can consider this to be adequately representative, and you've produced a fairly faithful precis of the reference, which I've tweaked a little. This and the spin were evidently both problems, but the spin problem does not come through as strongly at the moment. —Quondum 00:35, 15 September 2014 (UTC)

Thanks to Quondum for the clean up; it reads better now. Hopefully we are all encyclopaedic and in accordance with Wikipedia standards now. I know nothing of spin. Bdushaw (talk) 00:39, 15 September 2014 (UTC)

Thx - I was referring to the uncertainty principle, specifically, which is formally space-momentum OR time-energy. I agree with your explanation; it is perhaps not necessary to elaborate in the article (I am watching the length), but it bothers me a bit; some people might conclude the uncertainty principle is space-energy. I found a reference to a Heisenberg oral history where he talks about the beta particle and the nucleus. I might include it. Bdushaw (talk) 01:04, 8 September 2014 (UTC)

I have now added the momentum-energy argument as a footnote. Dirac66 (talk) 22:39, 9 September 2014 (UTC)

Q.: Is beta decay the first known instance of the creation of a particle? Was the issue with the nucleus that the creation of an electron in beta decay was a completely foreign concept at the time? I think that is right, but it has never been explicitly pointed out to me. Rutherford did a lot of work with alpha particles, but those were just parts of other atoms, not an entirely new particle created out of thin air (sort of). Where did they think gamma rays were stored? Bdushaw (talk) 18:07, 8 September 2014 (UTC)

Alphas were recognized as a collection of known particles which just emerged from the nucleus together, even if they had misidentified the particles as 4p + 2e rather than 2p + 2n. As for gammas, I think physicists did accept at the time that any form of light could be emitted (created) or absorbed (destroyed), by analogy with much earlier observations on visible light. Dirac66 (talk) 22:39, 9 September 2014 (UTC)

How have the alphas been misidentified as 4p + 2e rather than 2p + 2n?--82.137.15.208 (talk) 11:19, 13 September 2014 (UTC)

This statement referred to the proton-electron model of the 1920's. Since neutrons were excluded from the model, the alpha particle or He-4 nucleus was supposed to have 4 protons to give a mass of 4 amu, and 2 electrons (in the nucleus) so that the total nuclear charge is +4-2 = +2. This was the same reasoning as for N-14 which is considered in the article. Dirac66 (talk) 18:44, 13 September 2014 (UTC)

Answered my own question. I've developed the proton-neutron model subsection, rather tentatively. See what you think. Bdushaw (talk) 06:21, 9 September 2014 (UTC)

Notes for me, as well as suggestions for editors, the two discussions I have in mind next are a brief sketch in a new subsection on "neutrons in the 1930's" of how the neutron was used for research in the '30s (transmutation, fission, slowing of neutrons by paraffin or water to boost capture rates, c.f. articles Enrico Fermi Otto Hahn ); neutron has no charge hence can easily penetrate atoms; the road to the the A-bomb) and the discussion in the next section of how the mass of the nucleon is less than the sums of the masses of the parts, i.e. energy demonstrates stability. The article needs to briefly touch on/remind the equivalence of energy and mass somewhere. Also, the article presently has a bit of confusion about the terminology isotope v. nuclide which should be cleared up. I gather the former refers mostly to chemical properties, whereas the latter refers to nuclear properties; the terminology is a little fast and loose. Thanks for the tips above and corrections/additions to the article. I sense I may be drawn away to other things for the time being and may not have time to continue developing the article for now. Bdushaw (talk) 05:52, 10 September 2014 (UTC)

Some further clarification can be found in the article Nuclide. Dirac66 (talk) 19:39, 14 September 2014 (UTC)

Editorializing?

I see that some user has mentioned that the conclusion proved by Ambartsumian and Ivanenko in 1930 about the necessity of presence of a neutral particle in nuclei is similar to that by Rutherford in 1920. I also noticed that the statement of similarity has been removed by Quondum on grounds of editorialization. One may ask, what exactly is the editorializing aspect? Somehow the qualifier obviously?--86.125.181.101 (talk) 15:35, 19 September 2014 (UTC)

Just above where the statement had been added, the article says:

• Rutherford considered the required particle to be a neutral double consisting of an electron closely orbiting a proton.
• There were other motivations for the proton–electron model. As noted by Rutherford at the time, "We have strong reason for believing that the nuclei of atoms contain electrons as well as positively charged bodies..."
• Rutherford called these uncharged particles neutrons, ...

The first and second bullets are in direct contradiction with what I deleted as "editorialization". There remains a problem with the text though: it is not clear what "these uncharged particles" in the next statement refers to, though it presumably relates to the earlier statement referring to the "neutral double consisting of an electron closely orbiting a proton". To describe the statement in the article that "In 1930 Viktor Ambartsumian and Dmitri Ivanenko in the USSR found that, contrary to the prevailing opinion of the time, the nucleus cannot consist of protons and electrons" as "a conclusion obviously similar to that of Rutherford a decade before" is really, really stretching it. Would you care to suggest a term other than "editorializing" to describe this kind of misinterpretation? —Quondum 17:32, 19 September 2014 (UTC)

This very interesting discussion from here has some subtleties. The similarity between Rutherford's conclusion/statement from 1920 and the proof by A&I from 1930 is that both underline the necessity of a neutral particle in the nuclei, regardless of its internal substructure. There are two aspects that should not be conflated regarding the presence of electrons in nuclei:1) the presence of free electrons in nuclei which seems to have excluded by A&I and 2)the presence of bounded electrons in nuclei in the form of a neutral particle which has not been invalidated. The subtlety involved here is that somehow the two aspects have been conflated during the disproving of the proton electron model. The latter aspect (the bound electron in the neutral particle) has not been disproved even if proton electron model has been replaced by the proton neutron model. Also, a misleading piece of text that should be adjusted by clarification or elimination is the intercalation contrary to the prevailing opinion of the time by seeing exactly what the article by A&I really proves.--86.125.169.130 (talk) 18:35, 19 September 2014 (UTC)

We don't know quite what A&I really proved (see below), but the argument is that Rutherford suggested "neutrons" as not really particles, but a proton-electron combination. Whether closely bound or not is not really relevant. A&I argue, we infer from the text that was inserted, that electrons of any form cannot exist within the small confines of the nucleus, bound or unbound - quantum mechanics does not really allow a particle as light as the electron to be confined that tightly. However, I don't believe that A&I really had an accepted "proof" (see below); we are seeking references on that. Bdushaw (talk) 07:34, 23 September 2014 (UTC)

It is interesting to note that Bohr asserted that quantum mechanics is not applicable in the interior of a nucleus due to continuous spectrum of beta ray.--5.15.178.85 (talk) 11:00, 4 October 2014 (UTC)

Viktor Ambartsumian and Dmitri Ivanenko

Just to cast a bit of skepticism concerning this proof of the neutron before Chadwick's discovery. This result seems not to have been widely accepted, either at the time or in subsequent literature. The sentence here has two citations, one is in Russian (the technical result; not decipherable by me; I can find only a scan, so Google translate is no help - its all of three pages with no equations and no numbers, however; this "proof" can't be that definitive...), and the other is a biography. The biography " - a life in science" has this to say about the neutron:

There is yet another paper, written jointly with Dmitrii Ivanenko in the very beginning of his scientific career (Dokl. AN SSSR, ser. A, No. 6, p. 153 (1930)), that can be included in the list of the most outstanding papers on the structure of the atomic nucleus. Contrary to the prevailing opinion of the time that the nucleus consists of protons and electrons, they proved that free electrons cannot exist within the nucleus and that some neutral particles must be present besides the protons. In fact, this was a prediction of the existence of the neutron, made two years before James Chadwick discovered this particle.

From which you see the sentence in this article has been copied. The result may well be correct, I can't tell. But this result is not cited anywhere that I can tell. The wikipedia sentence in question has a slight whiff of propaganda about it. We don't want to be Western centric to be sure, but I would feel better about this sentence if there were, e.g., history of physics texts that discussed the result and put it in context. To some extent the issue is as I mentioned above - if we attempt a history of the neutron based on primary sources we will likely be confused; it was a confusing time. I think I advocate removing the sentence, unless a better reference for that discussion can be found. Bdushaw (talk) 20:08, 22 September 2014 (UTC)

Poking at the problem a bit more, I suspect the Ambartsumian and Ivanenko result pertains to the Klein paradox. According to the Dirac equation, an electron confined to a small region in a deep potential well is always transmitted. I have a reference that this paradox was one of the quantum mechanical objections to the electron-proton theory. (but this result was not by A and I). Bdushaw (talk) 21:14, 22 September 2014 (UTC)

I also thought this was a bit more of that classic Soviet "The Russians knew all that years before the West" stuff. The reason is that A. Pais in Inward Bound discusses the A and I paper and doesn't really think much of the claims of prescience for it. I've been meaning to get out the book and look up Pais' discussion, as it's the only one in English atomic history I've come across. Pais is usually quite reliable. I did some original historical research on early atomic models in college, long before Pais' book, and found him later to be pretty accurate on the history I knew from firsthand reading of the papers in the Phil. Mag., etc. He did his homework, so I trust him. SBHarris 22:02, 22 September 2014 (UTC)

I have read the paper in question and will try to explain its content. That paper does not predict that a neutral-charged particle we call neutron exists. It, however, does make a couple of statements:

• The nuclear electrons (authors at that point followed that model) and outer electrons are not "equivalent"
• Nuclear electrons are not "individual"

Also, the paper was more like trying to understand the data they had at that point, rather than anything (if anyone had any other idea), therefore both were not too strong statements, allowing some opposition to the ideas emerging in the article. And lastly, the side note in the end of the article says that the article was particularly interesting because it was the first to defy the idea nuclear electrons were individual (that page was printed when the neutron was known).

Feel free to ask more if there are questions I have not answered.--R8R (talk) 11:39, 23 September 2014 (UTC)

Thanks for the translation. I'm convinced that the assertion that A&I knew about the neutron is missing the mark. I'll comment out the sentence. Should an independent supporting reference for the issue reappear we can reinstate it. Bdushaw (talk) 13:51, 24 September 2014 (UTC)

What exactly is intended by the statement ″Nuclear electrons are not "individual"? Somehow that they are not free, but included in the neutral particle hypothesized by Rutherford?--5.15.47.12 (talk) 23:30, 26 September 2014 (UTC)

It's easier to have the link here: boom

I think so, but in fact, I don't know. They don't say that explicitly. Besides, I'm not sure they mean anything (they say, "Not individual," but that's it. They don't say, "But they are...," or "Because...", because they only note the mismatches of reality and the then-current theory and not propose an alternative one. They also note then-recent findings electrons in nuclei lose their momenta. They use the term "nuclear electrons" and don't doubt the existence of particles it stands for, at least aloud, so maybe they don't think electrons dissolve in protons or anything, but there's nothing more I could tell about their vision on that for sure).--R8R (talk) 17:27, 28 September 2014 (UTC)

The prevalent conception of proton-electron nuclei is discussed in a paper from 1930 by Ehrenfest and Oppenheimer Note on the Statistics of Nuclei in Physical Review [5] analyzing clusters of fermions.--5.15.178.85 (talk) 10:39, 4 October 2014 (UTC)

I have just encountered a mentioning of a paper (in German Neutronen und kernelektronen) about nuclear electrons by Ivanenko in Physikalische Zeitschrift der Sowjetunion, Bd.1, s.820-822, 1932 which is useful in the context of this discussion re the traceability of scientific reasoning.--193.231.19.53 (talk) 12:03, 6 November 2014 (UTC)

Nuclear electrons

Taking into consideration the above mentioned paper by Ivanenko on nuclear electrons I open here a new subsection to the purpose of summarizing the knowledge on nuclear electrons and its effect on the subsequent developments of the nuclear structure investigations.--193.231.19.53 (talk) 12:11, 6 November 2014 (UTC)

Important aspects to be mentioned in this section on nuclear electrons are those details regarding the inference of non-existence of nuclear electrons based on the measured nuclear spin of nitrogen-14.--5.15.33.80 (talk) 10:15, 9 November 2014 (UTC)

It be useful to mention the contribution by Franz N. D. Kurie to the disproof of nuclear electrons, but the quantitative details of the disproof seem to be missing on that page.--5.15.35.108 (talk) 18:19, 24 November 2014 (UTC)

I put here the link to a noticed paper by the suggested author Franz Kurie [6] to be discussed.--193.231.19.53 (talk) 14:32, 14 January 2015 (UTC)

Uncertainty principle

I was going to let it slide, but I can't stand it...I am sure you all appreciate the psychology! The section on the uncertainty principle now says This principle implies that there is a lower limit on the kinetic energy of a particle confined to a small region... I'm not sure that is true. Its my understanding that the uncertainty principle specifies distributions - if the particle has uncertainty deltaX, the width of the particle position distribution, then it has momentum distribution deltaP, the width of the particle momentum distribution. So with tiny deltaX, the electron still may have near-zero P, its just that the probability of that is insignificant. It has much greater probability of large P. I would have thought a statement like, This principle implies that a particle confined to a small region likely has large kinetic energy... Or have I misunderstood the situation? Bdushaw (talk) 06:11, 16 September 2014 (UTC)

You may remember ye olde particle in a box. If the particle has too little momentum, its wavefunction just won't fit inside the box, and so that can't happen. The minimum energy is the one with the smallest wavefunction that fits. In some ways I find this easier to understand than the uncertainty arguments, which narrow down a free space wave packet. If you have a box with solid walls (no fuzzy potential barriers), the wave packet becomes just one set of waves, and there's just one lowest harmonic-- the fundamental. And that has a certain minimal lowest frequency, which corresponds with a minimal lowest energy. This is really no more quantum mechanics than the lowest tone of violin string. The quantum mechanics comes in simply because particles act as waves, and the wavelength is connected to their kinetic energy. SBHarris 08:27, 16 September 2014 (UTC)

Humm - I understand that argument. But it is a little different than the uncertainty principle, isn't it? More like Raleigh-Ritz, if I recollect correctly. One has to assume a form for the potential well, perhaps, in this case. This argument should be written as something like Basic quantum mechanics places a lower limit on the kinetic energy of a particle confined to a small region... and dispense with the uncertainty principle. But what was the essence of the argument that was given in the 1920's? Bdushaw (talk) 10:14, 16 September 2014 (UTC)

A more correct statement would be This principle implies that there is a lower limit on the expectation value of the kinetic energy of a particle confined to a small region... Since a real nucleus has potential walls of finite height and finite slope, the problem only approximates the textbook particle in a box, so yes there will be some distribution of momentum and kinetic energy about the mean, but it is the expectation value which is important. I think though that this explanation is a bit too detailed for this article, and that referring to the uncertainty principle is simpler to understand. Dirac66 (talk) 13:09, 16 September 2014 (UTC)

Shultis & Faw do directly invoke the uncertainty principle, pretty much as it stands in the article. I agree with your intuition that the argument that the kinetic energy is related to the momentum distribution seems to be indirect, though it almost certainly rooted in the uncertainty relation: because energy and momentum form a four-vector of which the momentum part has a distribution of a minimum width, the energy part must have a related distribution in time with a proportional width (because |E|≥|p|). This is horribly hand-wavy and OR, but it shows that the link is there. This ties in with an expectation value as you put it. However, bound system exhibit discrete energy levels, with a lowest energy level. This in turn translates into an exact lowest energy, rather than merely an expectation value. —Quondum 13:37, 16 September 2014 (UTC)

How about This principle implies that the kinetic energy of a particle confined to a small region will be large.? Or even This principle implies that the expected kinetic energy of a particle confined to a small region will be large. (since I agree with expectation value, which may be viewed as a moment computed from the distribution. ) I think we have general agreement - But as for the article, however, the lowest ground state energy argument is not quite the thing, I don't think (one would need a reference for it). But for me at least the statement that the uncertainty principle specifies a lower limit seems incorrect. I also agree that a lengthy technical discussion would not be appropriate for the article; happy with the footnote. Bdushaw (talk) 17:18, 16 September 2014 (UTC)

I agree with your concerns. I've stripped that out; see what you think. The reference doesn't spend many words on it, and it may not be appropriate that we do. —Quondum 18:27, 16 September 2014 (UTC)

I think more details are required about how the uncertainty relation implies what it is assumed to imply. The details are required to show clearly how the unbound state of electron in the nuclei is excluded. The lack of details makes the assertion unconvincing.

Also it should be clearly specified that if the unbound electrons in nuclei are disproved, the presence of bound electrons in the form of neutral particles in nuclei is not disproved at all.--86.125.190.147 (talk) 12:18, 27 September 2014 (UTC)

This is a historical section, so the question is what was said in the 1930's. We need to check the sources again, rather than starting our own original discussion here on the quantum mechanics of the proton-electron model. Dirac66 (talk) 15:52, 27 September 2014 (UTC)

Of course, sources could be useful to check, like the recently inserted ref by Ivanenko in Nature (1932) and others.--5.15.30.143 (talk) 21:20, 27 September 2014 (UTC)

Yes, I'm also unhappy with the assertion as it stands; it needs more detail to be interpreted. —Quondum 15:53, 27 September 2014 (UTC)

I've looked at quite a lot of material on the historical neutron in recent weeks, and I've not found any specific publication from the time that makes the uncertainty argument. I'm suspecting that the notion was just circulating around among those concerned. There ARE references, some are noted, that the uncertainty principle was an issue. None of these arguments amounts to a "proof" that there was no nuclear electron, merely that it seemed more and more unlikely; more awkward. I think the article here threads that line. As noted above, the section is just historical - we should write only what is documented to have happened at the time, rather than attempt to branch out to modern-day, after-the-fact "proofs". And yes, the recent Ivanenko (1932) reference is rather sketchy - its a short one paragraph letter to the editor with some thoughts about the situation and no concrete analysis link - the entire paper, I believe. Here is a website that might be helpful on that ivanenko model; it has references. In lumping Ivanenko's contribution in with Heisenberg's the article is likely making a mistake, although I've not looked at the other Ivanenko articles from 1932. (I get the impression that most of the physicists of note were already convinced of the neutron, neutrino and fiction of nuclear electrons, they were just waiting for their discovery before they could move forward.) I am likely going to wander away from the article again; other pressing things and I've completed the various subsections I had in mind at the start. Its been fun. Bdushaw (talk) 03:39, 29 September 2014 (UTC)

We don't want to be creating urban legends on WP, and the claim of the confinement being a problem due to the Heisenberg uncertainty principle sounds still overstated by your description. Would you be able to dilute the statement or remove it in line with what you've found before you step off it? —Quondum 05:01, 29 September 2014 (UTC)

The references I've seen have been somewhat like link (see also Frisch's What Little I Remember, I think; and the Bohr Centenary book reference, which are similar) which states Eventually, however, calculations using Heisenberg’s uncertainty principle showed it was not possible for electrons to be contained in the nucleus. Such a statement would just be rather vague in the article...we'd get a "Why?" footnote added quickly (and besides, purely as a matter of English and logic, uncertainty principles do not show things, people do). I suspect that original references from 1930, with numbers worked out, are likely, e.g., personal letters. We don't even know "Who?" I don't think the sentence is overstated - the numbers are straightforward, based on h.u.p., and we have a reference for those calculations; we've just worked out, undergraduate style, what was meant by the statement; I actually would not consider that original research (or at least it is not very original... :) ). The sentences do not "prove" no electron, just show how unlikely it seems. One could add a sentence like that one, perhaps. I think I will let others have a go at the paragraph; I need to focus elsewhere. Bdushaw (talk) 06:24, 29 September 2014 (UTC)

Well, the statement seems to summarize what can be ascertained from what you've found: that it presented issues to the model, without giving much detail; thus, it is unclear that it can be improved. The statement you quote here is very strong, but unfortunately gives no "why". Thanks for all the careful work you've done. —Quondum 14:16, 29 September 2014 (UTC)

Pais's book Inward Bound arrived today and there is a summary of this question on p. 299. He has roughly what we have - uncertainty relation issues widely known, no specific person or number associated with them; this from Wigner personally, it seems. I thought that Gamow's book from 1931 would certainly have a discussion, but Pais says no. Pais says How can a beta-ray with energy a few MeV wait inside a nucleus to be released if its wavelength is large compared to the nuclear radius? and Moreover, the typical (relativistic) kinetic energy of a confined electron is greater than 40 MeV, implausibly large compared to the average nuclear binding energy per particle. Pais notes that other arguments were more compelling - the nuclear spin and statistics and the Klein paradox. The U.R. do not constitute a "proof", but they make things awkward for the p-e model. One has to resort to creative exotics to get p-e to work; plenty of people at the time were certainly willing to consider creative exotics. Bdushaw (talk) 20:39, 29 September 2014 (UTC)

I'll have to take the time to read through that chapter in detail. A glance suggests that Pais is basically saying that this argument seemed to be hand-waving at best: an argument of implausibility, not anything solid. In particular, it seems apparent that people at the time did not give this particular argument much weight, unlike the argument about spin. Anyhow, give me some time to read and see whether there is any change needed in the tone in the article on this point. At least this reference seems to be focusing on this precise issue, and seems suitable as a secondary source. —Quondum 22:05, 29 September 2014 (UTC)

I've given the paragraph a rework; see how you like it. There are countless references that make this argument, so at the very least something must be said about it, it seems. BTW, notice that these same arguments apply to quarks, and we see what exotic theory that entails. They are more massive than electrons, but perhaps more confined. Bdushaw (talk) 08:04, 3 October 2014 (UTC)

I have copyedited it slightly. I removed the last statement you added, as it applies to the collection of issues with the proton–electron model, and not specifically to the topic of the paragraph. I agree that it must be mentioned, but should reflect the tone of the literature; my impression is that the description uncertainty principle was more considered problematic than a problem. In my mind, the paragraph is actually very good at the moment. — Quondum 17:06, 3 October 2014 (UTC) — continues after insertion below

Klein paradox

I am somewhat concerned by the following paragraph about the Klein paradox. In particular, both the paragraph and the referenced article give no sense of the current status of the Klein paradox, and indeed seem to suggest that its conclusion might still be considered valid. While it may have been historically considered a problem, the impression I get is that it was a red herring (its conclusion appears to be reflective of an incomplete theory, not a problem with confinement of electrons), and it would be good to alert the reader to this. —Quondum 17:06, 3 October 2014 (UTC)

I think that's true, but I don't know enough about the Klein paradox to fix the paragraph. I gather the circumstances of the paradox turned out to be unphysical/pathological. Perhaps add "It was later shown that the paradox was artificial, and it was superseded by ..."? (I don't know enough about it, but there is a discussion of this paradox in Bjorken/Drell.) Bdushaw (talk) 20:37, 3 October 2014 (UTC)

The last sentence of the article on Klein paradox says that Many experiments in electron transport in graphene rely on the Klein paradox for massless particles. with references to articles in Nature 2006 and Science 2007. This suggests that some recent work takes the Klein paradox seriously, at least for massless particles in condensed-matter physics. Dirac66 (talk) 20:56, 3 October 2014 (UTC)

Reference [3] in that article (Klein paradox) gives a sense of what is behind this. They say that the Klein paradox is now understood (essentially in terms of interpretation of the tunneling particle being a positron, which we could understand as electron–positron pair creation). They are also very clear that they are talking about quasiparticles rather than electrons in graphene. They also say that the term "Klein paradox" has become used in a broader sense. So to reflect the meaning of existing references requires careful use of wording. —Quondum 21:47, 3 October 2014 (UTC)

Proton/Neutron articles

I made a comment over on the proton article talk page which I will also make here. The two articles (and other such similar articles) should likely have some similarity in design. In the proton article the History section is toward the bottom of the article, which I dislike. That article has as its first section a brief description of the proton, which I like. I contemplate a reorganization of the proton article and an introduction of a Description section similar to that in the proton article to this article above Discovery. Not anytime soon - Bdushaw (talk) 18:04, 16 September 2014 (UTC)

This goes to recommendations in science articles to have the History section at the very end, presumably so the young Turks can ignore the moldy old stuff more easily and get on with the latest fashion in understanding. Whereas the old farts, the older they get, become more and more interested in context and understanding of not just where we are, but long sagas of how we got here. You should see the fights in medical education!

In the chem elements articles I've pushed for compromise where history is about one third in, after properties and chemistry. At that point we do Discovery/etymology, which seems to segue well into physical history of nucleosynthesis and physical history in the universe once the reader is in the mood to look at the past. This then goes to isotopes and occurrence to geological occurrence, production, then applications.

All this doesn't work quite as well for short lived subatomics like the neutron but it's still a compromise I hope survives. The history of science on WP will take an awful beating if it doesn't.SBHarris 16:33, 19 September 2014 (UTC)

Excitement in the neutron lifetime

I just ran across this article: [7] in May 2014 Scientific American A curious discrepancy between bottle and beam measurements, that seems to have existed for some time. Bdushaw (talk) 21:40, 25 September 2014 (UTC)

It is already in a footnote in the article, but might deserve to be brought into the article text. —Quondum 22:28, 25 September 2014 (UTC)

Description section

I've started a new section to describe basic properties of the neutron at the start of the article, as mentioned above somewhere. Please have a look at it to correct or develop ad needed. It seems to me this is a good approach to begin the article - yes? One can get into logical trouble doing this, without an eye on the entire article. Bdushaw (talk) 20:17, 26 September 2014 (UTC)

hypothesis-model - recent changes

I've reverted back to an earlier version of the article. Changing "model" to "hypothesis" has a variety of consequences elsewhere in the article, and I'm not sure the change is warranted. Also, the word model is often synonymous with hypothesis in English, as it is used in the article. The "proton-electron model" phrase is used several places in the article, so changing this phrase requires quite a lot of revisions elsewhere. Heisenberg developed quantum mechanical description of n-p interactions, I believe, unrelated to the issue of beta decay. Can those that think changes are needed, first give a discussion of why they think changes are required here? Thx., Bdushaw (talk) 06:24, 9 November 2014 (UTC)

Of course some reasons for the need of the mentioned changes are useful. The first aspect involves the distinction between model and hypothesis. The distinction is necessary because a hypothesis can be purely qualitative while a model usually implies quantitative testable consequences (one can mentions models like the planetary Rutherford model of atoms, Bohr model. The connection to beta decay is given by the fact that emission of electrons from nuclei generated the hypothesis that nuclear electrons exist inside nuclei, but this qualitative statement/hypothesis was not included in a quantitative theoretical construction that could be called model. An explicit quantitative proton-electron model of the nuclear structure has never been developed as far as I know.--5.15.33.80 (talk) 10:06, 9 November 2014 (UTC)

I think I see what you are getting at, but I don't think I agree with your distinction between model and hypothesis. Let's see what others have to say. Like all things wikipedia it comes down to citeable sources - I've been reading quite a lot about this topic and can't recall this issue being referred to as a "hypothesis" in the publications. I'll take another look, however, and see how people are describing the topic in the literature. Whether model or hypothesis, in either case the issue was vague other than the general notion that there had to be an electron in the nucleus, with no physical picture as to how that was possible. Bdushaw (talk) 21:48, 9 November 2014 (UTC)

I can also see the distinction being made between model and hypothesis, but I'm not too sure that it is the semantically correct distinction. And while I expect a complete model to provide predictions, an incomplete model might not be able to do so in detail. This does not stop it essentially being a model. A hypothesis, on the other hand, IMO cannot be regarded as the qualitative equivalent of a model; it is the equivalent of a logical statement. So in my mind, "hypothesis" is certainly no better than "model" for this use. A significant factor is what it is called in the literature (and indeed if we had an article dedicated to it, we would have to use such a term). Pais, in Inward Bound – Of Matter and Forces in the Physics World, extensively uses the word model for this and related uses, as I suspect many others do. —Quondum 23:17, 9 November 2014 (UTC)

I see this discussion involving the hypothesis-model distinction and I must say that user Quondum is right in saying that a hypothesis is a logical statement. A model uses several (at least one) hypotheses. The distinction between the two concepts is useful to the clarity of the article by avoiding a false impression and vague wording. Usually more than one working hypothesis is involved in a model, so the distinction is necessary.--109.98.249.49 (talk) 10:20, 10 November 2014 (UTC)

I think that a wording that underlines the concept of nuclear electrons avoids the above mentioned distinction.--85.121.32.27 (talk) 12:50, 10 November 2014 (UTC)

Emilio Segre in his biography of Fermi also uses the phrase "proton electron model". We also have the historical context of the Thompson "plum pudding" model and the Rutherford model. Bdushaw (talk) 19:49, 10 November 2014 (UTC)

Unlike Thompson and Rutherford models, proton-electron model is not really a model. Biographical accounts can use loose wordings. The recently inserted ref by Schopper has on page one the sentence: The emission of electrons from nuclei gave rise to the hypothesis that protons and electrons are nuclear constituents.--109.98.249.49 (talk) 10:11, 12 November 2014 (UTC)

The use of hypothesis instead of model is not misleading. Also the mentioned source mentions some objections to nuclear electrons. One of them addresses the kinetic energy of the electrons of the order of 20 MeV. The esential condition of keeping the electrons inside the nucleus is the existence of an attractive interaction which can balance the kinetic energy of nuclear electrons.--109.98.249.49 (talk) 10:25, 12 November 2014 (UTC)

I don't buy either of these arguments for the use of "hypothesis":

• "the hypothesis that protons and electrons are nuclear constituents": this is a statement about an aspect of a model; it does not encompass the whole model;
• "the existence of an attractive interaction": again, this is a statement about an aspect of the model, which can be called a hypothesis, but is again not what is being described, but only an aspect of it.

—Quondum 13:52, 12 November 2014 (UTC)

As before, I object to the recent changes to the article. I believe that the "electron-proton model" language is substantiated - the recent changes are at odds with what appear to be common usage in the literature. In addition, the changes to the section on Heisenberg n-p model/quantum mechanics are just wrong. Heisenberg established that the n-p system could be quantum mechanical, irrespective of beta decay. It could be the language before was not clear (looked o.k. to me though), so perhaps it should be modified, but the language now is incorrect. Editors should wait for a consensus before reasserting their views of an article. Bdushaw (talk) 22:20, 12 November 2014 (UTC)

I certainly don't agree with any of this attempt to define and imbue "hypothesis" and "model" with any particular qualities that other doesn't have. In physics, things called "models" tend to be a little more complex as entities, I think, but any model IS just a big hypothesis (and a set of hypotheses is a hypothesis), and any hypothesis that connects the physical world of natural science and the ideal world or math and language IS also a model, so we're talking rocks and boulders, here.

Perhaps some of the confusion comes from subconsciously assumed types of models and hypotheses, both qualitative and quantitative. Models are metaphors or similes: we are saying that our natural science "thing" or "process" (and they are not the same-- note the time element), is LIKE something else (a geometric form, and/or an equation). The Earth is LIKE a ball. Or it is like an the ideal geometrical form "oblate spheroid" -- or whatever. Time is like a river. In quantitation, you can say the force and acceleration exhibited by a mass are LIKE the quantities given by the math expression F = m*a. There are physical models and math models and things that are both. The equation F = ma models the world, and that's our hypothesis that it does! But we know that isn't perfectly correct in relativity. And so on.

Sometimes physical models that have little quantitation (the electron-proton nuclear model) are slighted as being mere hypotheses and not real models, but that only means they are not mathematical models. The neutron-proton model wasn't all that mathematical, either, in the beginning-- you couldn't calculate with it. In QM we have a famous system where the math model is nice and stable, but the physical models keep changing (wave function collapse, many-worlds, pilot wave, Kramer transaction, etc). In some sense you pick your physical model on aesthetics, as they all give the same math and quantitation at the end. But it's all hypothesis, from one end to another. Any inductive statement about the world, which cannot by definition be analytically proven, is a natural science model. At the same time, it is, and always will be, an (unproven and unprovable) inductive hypothesis. SBHarris 23:53, 12 November 2014 (UTC)

"Fissile" ?

A friend of mine has given this article a read and noted the following:

In the 5th paragraph there is a line "caused by cosmic ray muons, and by the natural radioactivity of certain fissile elements in the Earth's crust." From my nuclear engineering days, the term "fissile" was reserved for something that could sustain a chain reaction and be used as nuclear fuel, such as U235 or Th232 or Pu239. U238 was called "fissionable". Do you intend to mean "fissile" or "fissionable"? All "fissile" isotopes are "fissionable" but not all "fissionable" elements are "fissile." Lower down in the section on fusion, this distinction is implied if not stated directly.

I also note that the supporting citation is just a link to the pdf of the article, rather than a proper citation. I do not find "fissile" in the article. Perhaps "elements susceptible to spontaneous fission" might be more correct. (I am hoping we can resolve the recent changes discussed above before additional layers of edits get stacked on them and they get Ukranianized....) Bdushaw (talk) 20:44, 13 November 2014 (UTC)

Yeah the term was meant as "spontaneously fissionable". Most of these neutrons are produced by Th-232 and U-238. SBHarris 21:30, 13 November 2014 (UTC)

E=mc^2

I've added a new set of sentences in the Description section on the equivalence of mass and energy. It seems to me the article implicitly assumes the reader is aware of this. But as I've noted elsewhere, I have eighth graders in mind with these articles so feel that something explicit should be said about E=mc^2 and energy densities. I am not at all confident that I've stated the issue in the best way, however - happy to have others clarify/elaborate. Bdushaw (talk) 02:55, 9 December 2014 (UTC)

If you look at the article on mass-energy equivalence which holds all of our E-mc2 stuff, you see why I think that even mentioning E=mc^2 is no more helpful in nuclear energy contexts than it is in chemical energy contexts. In neither case is the equation "explanatory". The source of the energy release in chemistry and in nuclear reactions is the pull of the fields (the field potentials) and the only difference is the nuclear fields are so strong that the energies become so large than their mass can finally be "weighed". But we could weigh chemical energy masses also, if our scales were good enough, and we don't use E=mc^2 as an explanation for the power of TNT. E=mc^2 only says that if you have a change in the energy of a system (as happens when some energy is released as heat and light) that you can weight the difference in the cold system left behind. But that mass can't be destroyed, as it deposits in whatever absorbs the heat and light that was liberated. So the mass is not "converted" to energy, but rather energy is converted from one type to another, and the mass goes with it, where ever it goes. If energy is conserved, mass is conserved also. A few moments after fission, the pieces of the nucleus as a system are just as massive as before (this is the invariant mass of the system)-- it's just that the rest mass has been converted to the relativistically-increased mass of moving particles. Even later, the "liberated" mass appears as heat. But hot objects are more massive than cooler ones, so again mass is there if you look for it.

Yes, the great power of the nuclear force is responsible for the energy release of fission and fusion, but in fission the mechanism is very subtle-- the nuclear force craps out due to distance effects, but the electric force is nearly as strong. So in fission the nuclear force is foiled by just a slight increase in distance and encourages greater compaction of the two fission fragments, so they ball up and no longer want to stick. Then the electromagnetic force drives them apart, up to their high speed, and provides all the power of the bomb. Most (~90%) of the power of a fission bomb, is due to the effects of positively-charged fission fragments repelling each other electromagnetically, until they hit something. Are we gunna explain all this HERE? SBHarris 05:00, 9 December 2014 (UTC)

Umm...well, no :) It just seemed to me that in several places the article implicitly assumes the reader knows about mass-energy equivalence and I thought that something should be said up front about it (e.g., masses listed as MeV/c^2). And the origin of the energy of nuclear power/bomb deserves a brief explanation, however handwaving. If you had to paraphrase the above for an eighth grader... Perhaps saying something like nuclear energy of reactors or explosives originates in a complicated exchange between nuclear and electromagnetic forces? The nuclear force is what compresses the electromagnetic spring? Everyone knows about E=mc^2, but perhaps encouraging that pop-culture is a mistake here. As I said, I am tentative about the sentences I added. Bdushaw (talk) 05:20, 9 December 2014 (UTC)

The nuclear force compressing the electromagnetic spring, so that fissile nuclei are all like loaded spring dart guns, is one of my own favorite analogies! There's a long discussion of the association of E=mc2 with nuclear effects in the popular mind at the end of the mass-energy equivalence article. Basically, it's sort of a historical screw-up. And yes, I don't mind hand-waving about interplays of forces-- that's how the thing works (though perhaps is more appropriate in the fission and fusion articles than here). I just don't want to open the unnecessary E=mc^2 can of worms if we don't have to. We indeed list masses as MeV/c2, but we would have to go down this alley with every particle article, and I don't want to! Same the space for things more directly neutron-related. I have more info to put in about the neutron magnetic moment, for example. And remember, neutrons are not converted to energy in a fission or fusion bomb-- in both cases there are just as many neutrons just after the thing goes off, as before. The loss of neutrons after that is rapid beta decay to protons in fission products and neutron-activated elements. Total baryons and leptons, of course, are conserved throughout. SBHarris 05:33, 9 December 2014 (UTC)

A bit of cross-editing at common purposes there, but hopefully we are converging on some appropriate text. It seems like something like this is needed, but if we end up deleting it all, that's o.k. too. Again, consider the eighth grader... :) Bdushaw (talk) 06:59, 9 December 2014 (UTC)

Tacit statements

I have noticed that user Bdushaw has removed some clear specifications from article by labeling them as weasel words. I think that non-explicit/tacit statements are not useful to the clarity of the article.--86.125.157.141 (talk) 10:57, 27 December 2014 (UTC)

Mass-energy equivalence is an assumed to hold when determining the mass of the neutron, without this assumption the mass of the neutron is more difficult to measure.--86.125.185.80 (talk) 17:20, 2 January 2015 (UTC)

I have reverted this. Following your reasoning every article should be made twice as long, adding explicit considerations and assumptions everywhere. - DVdm (talk) 17:35, 2 January 2015 (UTC)

Adding explicit considerations and assumptions greatly improves clarity without really adding too much length. We should keep in mind the 8th grader (who might be mislead by the lack of explicitness) as someone pointed out on this page.--86.125.160.200 (talk) 15:20, 10 January 2015 (UTC)

Dimensional inconsistency

I'have just noticed that some users keep opposing to explicit specification in the article with the label weasel words, even those have underlined the necessity of clarity for 8th grader.

The present equality formula for the mass of a neutron, when mass is summed with energy, is dimensionaly inconsistent in absence of explicit statement concerning mass energy equivalence.--94.53.199.249 (talk) 07:56, 13 January 2015 (UTC)

These various rationalizations are nonsense, and frankly a bit bizarre. The editor seems offended by the use of the term "weasel words" but this is a standard problem/phrase in Wikipedia style: weasel words. The edits in question are clear examples of weasel words. The editor has reverted several times under the guise of different IP addresses (all from Romania). Bdushaw (talk) 09:45, 13 January 2015 (UTC)

What are this claimed clear examples of weasel words? Considered? It does not appear on list in WP:WEASEL. Let's not include/confuse words which characterize the scientific reasoning style like considered and assumed/hypothesized with weasel words. This labeling would have consequences on all proofs from mathematics or mathematical physics which use these words. We could ask a wiki-mathematician like user:Tsirel how he views this issue.--94.53.199.249 (talk) 23:23, 13 January 2015 (UTC)

One disturbing aspect/assumption is that referring to IP geolocation discrimination. So what if the (IP)users that have pointed out problematic aspects/implicit assumption are all from Romania? But I see that even Bdushaw said something about implicit assumptions. But the real bothering (implicit) assumption is that Romanian IP-users are the same person, as if other possibility were excluded ab initio. Bdushaw has some (implicit?) expectation that any other IP from Romania who might intervene in this discussion should not be allowed to express his objections--94.53.199.249 (talk) 00:20, 14 January 2015 (UTC)

Register an account and you will get rid of speculations about posts only very likely by you really being posts by you. I actually agree with you about the weasel words. Weasel words are used to make something unscientific scientific. I read your word the other way around. I think you try to make something scientific unscientific by putting doubts in the readers mind. Either way, the words can't stay. YohanN7 (talk) 00:32, 14 January 2015 (UTC)

Please do not see doubts where there they are not by a problematic reading between the lines based on a false impression. And do not discriminate IPs.--94.53.199.249 (talk) 09:42, 14 January 2015 (UTC)

IP is right on the IP vs. account thing. Why do I have to get an account to be treated equally? What is the basis for that? Wikipedia is a free encyclopedia? If even you could prove it, and not just speculate (but it seems to me you can't), that's not the point. The thing of consensus (a basic idea Wiki is built on) is not about how many yeas and nays, but about who seems to be right and/or finding a compromise. If it can't be reached, get more people involved (say, there are Wikiprojects). If it still doesn't work, there are rules for that. You know these rules of the Wiki diplomacy. You can always win without going down to anything your opponent is/does (if your idea is good enough). Please keep the discussion focused on the article problems and by doing that, make the inside of Wiki better.--R8R (talk) 02:16, 14 January 2015 (UTC)

Well said, R8R. The discussion should be focused on content, not the persons of users.--94.53.199.249 (talk) 09:33, 14 January 2015 (UTC)

Why do I have to get an account to be treated equally? I'll never treat a crank (person) using several ip's the same way as a registered user. This is not an election in a democracy where it is possible to cheat. YohanN7 (talk) 11:33, 14 January 2015 (UTC)

Keep your unprovable allegations to yourself. It is utterly irrelevant who underlies the necessity of clearly expressing tacit assumptions, whether different IPs are really different users or not does not influence the need for clarity required by a reasoning. Please familiarize yourself with scientific proofs.--94.53.199.249 (talk) 16:14, 17 February 2015 (UTC)

At the risk of adding fuel to the fire, I'll try to explain my understanding regarding the phrases in question. "which is assumed to hold" Assumed by who? It is just vague. And are we to understand that the mass-energy equivalence is "assumed", that is without actual factual basis, so that it may turn out someday to be otherwise when we get actual scientific proof? Nonsense. "considered to be": Considered by who? It is just vague. And are we to understand that the three-quark content of the neutron is only just generally "considered" and may turn out to be otherwise when we get actual scientific proof? Nonsense. In this regard, I agree with YohanN7 that the words here serve to put doubt in the reader's mind, where no doubt is justified. There are other examples of weasel words near the top of the page for proton which should be fixed: a proton is now understood to be composed of three valence quarks: two up quarks and one down quark. The rest masses of the quarks are thought to contribute only about 1% of the proton's mass. - "understood" by who? "are thought" by who? I'll remove those phrases if no one gets to them before me. Other thoughts occur to me, but I'll let it go. I've tried very hard to choose words carefully and parsimoniously, particularly in that brief Description section; the words in question are neither necessary nor clarifying; they are in fact misleading. Bdushaw (talk) 04:13, 14 January 2015 (UTC)

Assumed for the sake/convenience of the proof by anyone checking the proof. You should familiar with proof style and not see doubts when there aren't any.--94.53.199.249 (talk) 09:36, 14 January 2015 (UTC)

Scientific style is based on proof and hypothetico-deductive approach.--94.53.199.249 (talk) 09:44, 14 January 2015 (UTC)

The EM force in fission

This sentence was removed: "Ultimately, the ability of the nuclear force to store energy arising from the electromagnetic repulsion of nuclear components is the basis for the energy that makes nuclear reactors or bombs possible." I put it back in because that's what happens. It could be clarified, but ultimately nearly 180 MeV of energy is produced in the fission fragments because they repel each other due to being positively charged. That's not true of where the NEUTRON energy comes from (of course), but it certainly describes where the fission fragment kinetic energy comes from. It's where most of the energy of a fission bomb comes from, in fact. SBHarris 02:47, 11 December 2014 (UTC)

Just to check my physical picture: The nuclear force binds nucleons together much like billiard balls held together by strings. If you cut the strings, the balls will fly apart, but only insofar as the kinetic energy they had within the nuclei. The electromagnetic force is like also connecting these billiard balls with a long-range, compressed, repulsive spring. When the string is cut the balls fly apart from both the kinetic energy they had within the nuclei and from the spring releasing its potential energy. The nuclear force may be strong, but it is only short range and at short range it balances the EM repulsion. The EM force may be weaker, but not so weak at short range, and it stores a great amount of energy in forcing charged billiard balls together.

I've been puzzling over neutron scattering, e.g., neutrons slowed by paraffin. I had viewed them as billiard balls, that is, hard spheres bouncing off one another, but that's not right. A neutron striking a proton must essentially be bound briefly to it, only to fly apart by the kinematics - a neutron scattered to the right, must have passed the proton on the left (or exchanged identities with the proton). Its quite a bizzaro little world...(who's in charge of this place???) Bdushaw (talk) 23:20, 11 December 2014 (UTC)

Related to this recent discussion above, a question: The article notes that neutrons are produced in nuclear fission (c.f. the new figure). Why aren't protons produced, or are they? One would think with their positive charge they would be more inclined to escape the nucleus than neutrons. The only thing I can think of is that the nature of the quantum mechanical system of the nucleus makes them more tightly bound, or more likely to be bound to the fragments from the fission process. Bdushaw (talk) 01:24, 15 December 2014 (UTC)

Proton emission does occur. I'll speculate handwavingly as to why this does not appear to occur frequently (or at all?) during fission (which I'll define as fragmentation with at least two fragments having more than one nucleon): The stable ridge of neutron/proton ratio is very narrow and curves with atomic number, so that the resulting fragments would almost inevitably be neutron-rich. This would suggest that further loosing free proton would be energetically unfavourable. —Quondum 02:37, 15 December 2014 (UTC)

The handwaving argument above sounds good, but (alas) proton emission does occur quite frequently in ternary fission, which happens in a small fraction of fissions both neutron induced and spontaneous. In that case, the 3rd positive particle is most often an alpha, but it can be everything from a proton to an argon. In binary fission, rarely is anything below Z=30 seen.

The processes that drive out delayed protons are quite different from neutrons, of course. The Coulomb potential drives out protons just like alphas, whenever the nuclear binding potential has been penetrated by tunneling, or else surmounted by some kind of "shockwave" from a nuclear breakup. The last is something like the loss of billard balls from the racked group when hit by the cue ball after a "break". Anything can happen as one ball hits another and that one hits one next to it. If you think about it, that's really the only way a neutron ever gets kicked out, as neutrons have every reason to stay and none to leave a nucleus. Near the neutron drip line where there's a huge excess of neutrons, little shocks like beta decay or inverse beta decay can liberate a loosely-bound neutron. But fission fragments are far from either the neutron or proton drip line, so they all need something a lot more energetic.

I don't know if anybody really understands this (I certainly don't), but something like the focused shock wave in a rack of billiard balls must happen, and it piles up on one nucleon and kicks it out. We know that nucleon emission happens very fast after the nucleus is struck by a neutron, or else undergoes the energetic inward collapse of a new proton, after beta-decay of a neutron. The time is only the time it takes the neutron to cross the nucleus and get out. Thus, a new neutron or proton emitted far from the drip-line, comes out immediately, with no waiting, because it's been kicked out.

By contrast, the only time you get (delayed) proton emission with a half life, is near the proton drip line, and it happens much like alpha decay, by tunneling of a particle that wants to escape the Coulomb repulsion anyway. But in fission that's not the mechanism for loss of either single neutrons or protons. They don't tunnel-- they are shoved out by a sort of knock-on shock, and it happens instantly. As for neutrons, there is no true "delayed neutron emission" by any mechanism. The delay for "delayed" neutron emission is beta decay and then the neutron emission follows promptly. The same is true of proton emission in ternary fission, since you are too far from the proton drip line for protons to tunnel with a delay; indeed as pointed out above, these nuclei are all proton-poor, since they are fragments of heavier elements. Thus, fission fragments don't generally undergo positron decay and electron capture and the kinds of things that happen to proton-rich nuclei in other circumstances. Proton emission in fission is like neutron emission in fission-- a far more energetic event than radioactive decay emissions. SBHarris 03:53, 15 December 2014 (UTC)

That's a nice description and presumably fully answers Bdushaw's question. From the premise that there is no mechanism of free neutron emission that does not involve some form of excitation (excess energy), there is no energy decrease in a neutron being emitted: i.e., that cold neutrons would endlessly be absorbed by any nucleus, with the possibility of decay through some other mechanism such as beta decay. This should be testable as the liberated energy of (electron) beta decay (including rest mass energy) being less than that for a free neutron, further minus the energy of forcing another proton into the nucleus. —Quondum 14:41, 15 December 2014 (UTC)

Not really that clear to me, other than its clearly complicated. I suspect the answer may be that if protons want to leave, they likely do so (energetically favorable) in the form of an alpha particle. It does seem clear that individual neutrons break free more readily than individual protons, yes? Bdushaw (talk) 04:23, 17 December 2014 (UTC)

You're right, that bit didn't get a clear answer. I suppose another one would be to figure out why it can be energetically favourable for a neutron to decay into a proton despite the high local positive charge. All rather more complicated than my understanding level. —Quondum 07:04, 17 December 2014 (UTC)

A physics professor I know has waded in on the question of why neutrons are scattered about, but not protons:

I think the tendency for individual, unbound neutrons to be emitted in fission, as opposed to protons, is pretty well explained, qualitatively at least, by the "valley of beta-stability" of nuclei, i.e., the excess of neutrons over protons in stable nuclei, which grows more than linearly with atomic number or mass number. (Specifically, the neutron excess, N - Z, grows approximately proportional to the 5/3 power of A, the total number of nucleons.) Hence, when fission occurs, the resulting fission product nuclei tend to be neutron rich, and, in particular, tend to be unstable against beta decay in which the excess neutrons convert to protons. (This is why nuclear fission reactors are such prolific sources of anti-neutrinos, rather than neutrinos, which are emitted in the reverse process: protons converting to neutrons.) But, for the same reason, the fission process can give rise to slightly more stable nuclei (in terms of the relative proportion of protons and neutrons) with the excess neutrons being emitted as unbound particles, singly or multiply.

The "valley of beta stability" is itself the result of the point you make, that, because of Coulomb repulsion the nucleus should tend to be unstable against breaking up, with the protons flying apart. This is why heavier nuclei increasingly need more of the electrically neutral neutrons to provide sufficient attractive strong nuclear force to keep the nuclei bound. So, for stability, the excess of neutrons over protons has to grow more than linearly with A.

I think that makes sense - those heavy nuclei undergoing fission have many more neutrons than protons. Bdushaw (talk) 22:29, 9 February 2015 (UTC)

It explains, empirically, that excess neutrons are eliminated in association with fission. It does not explain the process of neutron emission, and in particular, where the energy comes from to overcome the nuclear binding force holding the neutrons in place. After all, there is an alternate neutron reduction mechanism: beta decay. Clearly, there is some mechanism that makes it energetically favourable for excess neutrons to be expelled from neutron-rich nuclei, and we are not seeing what this is. At first blush we have a powerful binding force (the nuclear force), and no apparent mechanism of repulsion. I'll make a suggestion: the Pauli exclusion principle ensures that some of the neutrons in neutron-rich nuclei have high momentum and hence kinetic energy, which liberates them.

There is a related observation (really diverging here): it is rather curious that the range of stable nuclides for each atomic number is so very narrow, yet that there the range of atomic numbers over which there are stable nuclides is so large, despite meandering so much, with so many complex mechanisms at play. After all, one would expect that as Coulomb repulsion grows, we'd just get instability. Yet somehow, the nucleus's tolerance for high neutron density paradoxically grows at just the right rate to balance this instability. The "need more of the electrically neutral neutrons to provide sufficient attractive strong nuclear force to keep the nuclei bound" mentioned above doesn't explain it; it merely says that if it isn't there, larger nuclei would be unstable. The whole precarious balance seems kinda weird. —Quondum 00:46, 10 February 2015 (UTC)

Yes weird - our cosmos seems to be built on miraculous chances! I note that the neutron excess after fission is alleviated by two mechanisms: the departure of a neutron, which I assume occurs as you say because it gets sufficient kinetic energy out of the violence of fission, and the beta-decay of the neutron as noted above (why reactors have an abundance of antineutrinos). Bdushaw (talk) 01:34, 10 February 2015 (UTC)

"Weird" and "miraculous". I think you guys are heading in the direction of the anthropic principle. Dirac66 (talk) 02:01, 10 February 2015 (UTC)

Amen, brother... :) (When we start to imbue the article with faith-based science, please correct us appropriately.) Bdushaw (talk) 02:46, 10 February 2015 (UTC)

Yeah, that's not part of my normal vocabulary; I was getting a bit whimsical. My normal term would be "counterintuitive" or "curious". This particular observation doesn't even fit with the anthropic principle, since it seems that would involve tuning more than the limited number of degrees of freedom avaiable.

Back to my earlier statement: I did not mean kinetic energy from the fission event. I meant that when identical fermions are packed too tightly, some of the quantum states are necessarily high-momentum states, and in the neutron-rich nucleus, the Fermi energy may be higher than the binding energy. The neutron pressure could simply be so high that it expels neutrons, without the need for any violent events. See Neutron emission. —Quondum 04:46, 10 February 2015 (UTC)

Majorana peacockery?

Back in October a contributor removed the sentence: To the brilliant young physicist Ettore Majorana in Rome it was obvious that these results required a new neutral particle., calling it peacockery and arguing that it contributed nothing to the article. There are elements of truth to that, but: I think the sentence illustrates the international nature of the interest in the neutron and that others were thinking about it, and it was obvious to at least some people that this was a new particle. I was surprised in this topic at the extraordinary faith that many of these guys had that there were only two particles, proton and electron. The Majorana incident is also well documented. So I am suggesting restoring the sentence. Any objections? Thoughts? Bdushaw (talk) 04:32, 17 December 2014 (UTC)

Yes, that was a somewhat tendentious information Tetra quark (talk) 04:38, 17 December 2014 (UTC)

I've noticed that source nr 43 in the article by L. Brown and H. Rechenberg contains quite many historical data on nuclear structure and neutron, including Majorana's contribution, from what I remember. Someone with access to the full text of the source could add details.--5.15.26.123 (talk) 13:10, 20 December 2014 (UTC)

I would include a mention of Majorana's contribution in less enthusiastic and more encyclopedic terms. Perhaps The Italian physicist Ettore Majorana proposed that these results required a new neutral particle, with the same source. Readers who want to know more about Majorana can read the linked article on him as well as the referenced source article. Dirac66 (talk) 16:34, 20 December 2014 (UTC)

References

Ivanenko Revisited

I've modified the discussion on Fermi theory to clarify the contribution by Ivanenko. I must say I am not very satisfied by the continued claims for precedence by Ivanenko for things - the cited articles are often thin and often seem to amount to little than "It could be like this!" with perhaps the kernel of truth lost amidst a bunch of other erroneous suggestions (e.g., nuclei composed of neutrons, protons and alpha particles). Its rather peculiar to, after the fact, go back and cherry pick the correct things, ignore the wrong things, and say Iwaneko had it first! It doesn't help that the articles are often in Russian, French, or German in often obscure journals. The most recent references I found on this blog: D.Ivanenko’s proton-neutron model of atomic nuclei of 1932 where pdfs of them can be downloaded. I admit that it is hard for me to make an objective assessment as to Ivanenko's contributions and what precisely the impact they were to others. For example the famous Fermi article does not cite Ivanenko's articles, and I doubt that Fermi was aware of them (likely aware of Ivanenko himself, however). Unlike the Ivanenko articles, Fermi worked things out specifically, leading to predictions for e.g. neutrino mass; a much more satisfying theory. Yet, there is likely a western bias in the available references. I thought all this was worth a mention - just something to keep in mind, perhaps. Bdushaw (talk) 20:51, 5 January 2015 (UTC)

Perhaps we can ask the owner of the blog to specify some clarifying details. He is (among others) a nuclear theorist.--86.125.160.200 (talk) 15:08, 10 January 2015 (UTC)

"Its rather peculiar to, after the fact, go back and cherry pick the correct things, ignore the wrong things, and say Iwaneko had it first!"

Yes, indeed. It's interesting to go back to Pauli's Dec. 4 1930 letter ("Dear Radioactive Ladies and Gentlemen") where he predicts what he calls the "neutron" in the nucleus. We pass over this today and simply say he was predicting the modern neutrino, and he was. But Pauli's nuclear "neutron" does more than just fix up conservation of energy in beta decay. It also fixes the nuclear spin problem in Li-6 (which Pauli names in just this way) and nitrogen. Remember Li-6 and N-14 are 2 of the only available stable "odd-odd" nuclei available for examination (the others being the undiscovered H-2 and B-10).

Pauli's "neutrons" (see his letter) were low-mass particles with spins of 1/2 that sat in the nucleus opposing the nuclear electrons, cancelling spin in pairs when in even numbers, obeying the Pauli exclusion principle, and thus accounted for all the "sins" of the extra nuclear electrons which did the same (i.e., sat in the nucleus in pairs, with only odd ones contributing nuclear spin). The nuclear electrons gave spin-prediction problems mainly in odd-odd nuclei, at this point.

Remember the picture in 1930. Physicists were perfectly aware that there was a Li-7 and an Li-6, and they called them that! Pauli does. They "explained" these by postulating that Li-7 had an extra nuclear electron and an extra proton. But it had the wrong spin for this, like nitrogen-14. So Pauli suggests that every nuclear electron is accompanied by a nuclear "neutron" which is just as light, and contributing a spin to neutralize that of the extra "proton" that goes with every nuclear electron. In beta decay a nuclear electron goes off with the neutrino and leaves its proton.

This is very close to the modern picture. Instead of electron and neutrino created at the moment of beta decay, in Pauli's picture they are all there in a stack, contributing spins in the nucleus: thus, each of what we view as a modern "neutron", in Pauli's nucleus-view is instead a 3-complex of 1) extra proton, 2) neutralizing nuclear electron for it, and 3) neutral light neutrino to contribute the needed spin to fix N-14 and Li-6. In both of the later, the last odd neutrino would give a spin of 1/2, the last odd proton a spin of 1/2, and the nuclear electron for the extra proton would have a spin to cancel it, so as give a (needed) net spin of 1. Same for nitrogen, where we need 7 nuclear electrons, 7 extra protons, and 7 Pauli "neutrons." All paired by kind to giving a net spin of 1/2. Instead of 7 modern neutrons doing the same.

Pauli almost has it, here. It he'd thought of his triple-decker extra protons-electron-neutrino's as a (new) nuclear particle with about the same mass as a proton (which it must) and also with spin of 1/2 and separately following exclusion statistics, he'd have had the modern picture. So close! But that would have forced him to invent TWO new particles at once-- a neutral heavy one, and a neutral light one. The explanation he came up with is actually the most parsimonious. Too bad for Pauli that nature was ugly and didn't follow it. SBHarris 01:44, 14 January 2015 (UTC)

In thinking about this issue it occurred to me that there are three basic types of contributions to particle physics in this time period: (1) The basic measurements by experiment, e.g., the discovery of the neutron, or Fermi's measurement of enhanced cross section for slow neutrons, (2) development of theoretical descriptions, e.g., the Schrodenger equation, Dirac equation, Fermi's 1934 paper, and (3) interpretations that lend understanding and reconcile (1) and (2), e.g., Bohr's complementarity principle, or Rutherford's 1920 model for the nucleus. In the 1920's, 30's the Nobel Prize committee seems to have given much greater weight to (1), with the exception of Schrodenger/Heisenberg's theory for quantum mechanics. I don't know that an example of (3) has ever been awarded a Nobel prize. Ivanenko seems to me to have mostly contributed to (3) - interpretations and possibilities. Admitting ignorance, really, I don't know that Ivanenko ever measured anything pertaining to the neutron in the 1930s, and I don't know of a specific theoretical development or formalism that he developed that let people calculate and predict aspects of particle physics. Interpretations are valuable and essential to physics. That said, they seem to me a lessor cousin to (1) or (2) mainly because one can interpret and suggest new ideas all day long, yet not have REALLY nailed down what is really going on. Pauli's example above is like this - a quite fruitful interpretation that led to other developments, yet Pauli would never have gotten credit for the discovery of the neutrino; the considerable work he did on this did not nail the issue down sufficiently.

I conclude that it is a mistake to include Ivanenko's contributions at the same level as Heisenberg's or Fermi's theories. As important as they are, and several references I have state generally that "Ivanenko was involved", they don't seem to have been accepted as establishing facts with undeniable certainty. By suggesting possibilities, Ivanenko cannot claim credit for discovery.

As just an idea, that I don't really advocate at this point, I thought about a section on history of interpretation to review the various avenues that people thought about, including Ivanenko. Having said all that, I'm not sure I can suggest a change to the article...I think I merely have a clearer idea of what was bugging me.

Bdushaw (talk) 04:50, 14 January 2015 (UTC)

Charge vs. charge limit

To Bdushaw: I think your edits to the infobox today risk seriously confusing some readers into believing that the neutron does have a small net charge. I believe that what you meant is in the third of your 3 edit summaries: the value given is the charge limit, or the experimental uncertainty in the measured value of zero. In that case we should say something like (2±8)×10⁻²² e, consistent with zero. Or better, since the infobox is intended for very quick reference, put 0 in the infobox and explain the experimental uncertainties in a new subsection of the Intrinsic Properties section. Dirac66 (talk) 12:14, 19 January 2015 (UTC)

Yes, I wondered about that... Your solution seems more clear. My first thought was that the infobox was a summary of precise values. Happy to move the experimental limits to the Properties section. Bdushaw (talk) 23:20, 19 January 2015 (UTC)

Better now, thank you. Dirac66 (talk) 01:28, 20 January 2015 (UTC)

Magnetic moment - developments

I've been developing the page for the neutron magnetic moment this weekend, but fear I may have got out ahead of myself with my understanding...a review by interested editors is requested. In the meantime, the article on the proton magnetic moment seems both unintelligible and wrong, if that were possible, or perhaps I my understanding of the situation is seriously amiss. Bdushaw (talk) 23:20, 19 January 2015 (UTC)

Even with my limited level of understanding, it is clear that proton magnetic moment is gibberish. There is probably nothing wrong with your understanding. —Quondum 23:53, 19 January 2015 (UTC)

I've developed a paragraph on the history of the measurement of the magnetic moment...a surprising amount of drama and turmoil! Bdushaw (talk) 02:07, 21 January 2015 (UTC)

And there a is chance that Q is kidding with you. I would not trust him. YohanN7 (talk) 03:05, 21 January 2015 (UTC)

Not sure what to make of the above comment - Quondum recently replaced the top paragraph for proton moment with something at least intelligible. I was about to do that, but thought I should pause for some affirmation first. You may have just seen the new paragraph; you should see what was there before... Bdushaw (talk) 23:51, 21 January 2015 (UTC)

Unicode formatting problem?

In looking up how to format fractions on Wikipedia, I noted that text or symbols in unicode are discouraged. The issue seems to be portability to devices other than PCs. I believe that expressions such as ½ħ are both unicode symbols. I have been editing which such symbols since they look nicer (to me anyways), but it seems we should use a different format for such things. Do I understand the situation correctly? I'm not sure I'm happy with the alternatives, but 1/2 looks ok at least. What do people think? Bdushaw (talk) 23:48, 21 January 2015 (UTC)

To clarify perhaps, the issue seems to be fractions, more than a general avoidance of unicode. The <math> </math> approach may be preferable. Bdushaw (talk) 04:20, 22 January 2015 (UTC)

Agreed about the fractions issue. I'm not a fan of inline <math>, but there are templates that do a not-too-perfect job in HTML: {{frac}}, {{sfrac}}. —Quondum 04:44, 22 January 2015 (UTC)

{{frac}} seems to be discouraged as well, but {{sfrac}} seems o.k. So, if not <math>, then we seem to be left with {{sfrac}}, as in 1/2ħ...(but that makes the fraction too big!). Perhaps just 1/2ħ. Bdushaw (talk) 06:08, 22 January 2015 (UTC)

On the other hand, the article Spin-½ seems to use unicode fractions with abandon, including in the title, so perhaps we shouldn't worry too much about it... Bdushaw (talk) 06:52, 22 January 2015 (UTC)

My observations are:

• The {{frac}} template is only discouraged for mathematics articles, so this does not seem to apply (this is a physics article with extremely limited mathematics content).
• None of the ways of displaying a simple fraction are great. There will inevitably be display quirks for some browsers and fonts, and there are several kerning issues (line height, offset from baseline). This is a longstanding problem with mathematics (and physics) articles, which has occasioned much debate.
• Another option is ħ/2. 1/2ħ seems too ambiguous.
• I fully agree that it is not worth worrying much about; do whatever "feels" right.

—Quondum 15:05, 22 January 2015 (UTC)

Kurie/Magnetic moment

The recent addition concerning Kurie and the proton-electron model for the neutron and the measurements of the magnetic moments raise some interesting questions. First, however, I don't believe we can state that Kurie is accredited with "proving" the neutron was not a proton+electron. I know of no substantive reference that states that. The quote on the Kurie wikipage to this effect was copied from this website on Kurie at the Lawrence Berkeley Lab. The cited contemporary newspaper report on the result is hardly definitive. Also, the neutron magnetic moment (which see) seems to have been measured simultaneously by three groups. The Tamm/Altshuler estimate had problems; they estimated -0.5 muN. There were errors and skepticism about that estimate. I don't believe we can state that they had the first measurement, or conceived the neutron had a magnetic moment first. My sense is that Otto Sterns (shocking) measurement of the proton's magnetic moment in 1933 made the quest for the neutron's magnetic moment obvious and paramount. There was an interesting comment paper on the issues by Breit and Rabi (Breit, G.; Rabi, I.I. (1934). "On the interpretation of present values of nuclear moments". Physical Review 46: 230.), which I have transcribed for the time being here; worth a read.

The proton-electron notion for the neutron seems to have persisted for a few years after the neutron's discovery, but I know of no result that definitively concludes the neutron is elementary. One can argue that Kurie at least ruled out a couple of specific models for n=p+e. Chadwick and Goldhaber seemed to have accepted the neutron as elementary right away, particularly given the Fermi paper. But the Breit-Rabi paper cited above still clings to the notion. Neither paper cites Kurie. My sense is that the notion that n=p+e persisted for a little while for some people, but was quietly abandoned. Certainly once Fermi's paper had traction the issue was done.

The history of the magnetic moment of the neutron is an important issue worth mentioning in the article. Not sure what to say about the lingering proton-electron model; I think I tend to prefer leaving the issue out entirely - it has little substance and no supporting references. Bdushaw (talk) 14:02, 4 February 2015 (UTC)

Does the ref (44) The origin of the concept of nuclear forces by Laurie Brown say anything about Kurie? It would be very interesting to know.--193.231.19.53 (talk) 11:53, 7 February 2015 (UTC)

I don't have the book, but the link on the reference goes to the googlebook. A search there finds no mention of Kurie in the book. I do have Gamow and Critchfield "Theory of Atomic Nucleus..." (1949) which also does not mention Kurie, though they briefly review the notion that n may be p+e. I also have a great stack of biographical books on the history of physics during this period...all with no mention of Kurie. I think I have a plan for how to briefly discuss the issue, but I'll wait a day or two for more commentary, if any. Bdushaw (talk) 23:11, 7 February 2015 (UTC)

BTW, does anyone have a reference for how/why/etc E.O. Lawrence believed n=p+e? I can find no mention of that anywhere. A reference would be nice for that. Bdushaw (talk) 23:19, 7 February 2015 (UTC)

I see these sources mentioned here on Lawrence and Kurie. I wonder if the three volume encyclopedia Twentieth Century Physics by Abraham Pais, Laurie Brown and Brian Pippard mentions something about the aspects discussed here.--5.15.17.38 (talk) 21:35, 8 February 2015 (UTC)

Revisions - Neutron history

I've made a set of revisions concerning the history of the neutron after its discovery. The revisions reflect several Talking dialogs above, and the narrative at the James Chadwick article. I feel the narrative is a bit more accurate now, though could not vouch for 100% correct. I do not find the Kurie argument compelling, but certainly find the Kurie reference worth mentioning. Bdushaw (talk) 04:12, 10 February 2015 (UTC)

I've revised the narrative concerning the early measurements of the neutron mass - that is a tricky one. I hope I got it right! The reference to the biography of Lise Meitner was most helpful. Bdushaw (talk) 05:59, 11 February 2015 (UTC)

Spins and the nucleus

The latest addition to this article gives the following sentence: But if the spins are expressed by translation as multiples of 1⁄4 h/π both spin quantum numbers are integer and the difference between half-integer and integer disappears. I don't know what this means - it seems nonsensical to me. If we can't explain what the point might be here, perhaps we should remove the (uncited) statement. Bdushaw (talk) 02:34, 19 February 2015 (UTC)

I will remove it. Presumably the editor is making the arithmetic point that all spins are integer multiples of h/4π. But of course this is of no significance since there is still a difference between even and odd multiples of h/4π. More important, most (or all?) the scientific literature expresses spin as multiples of h/2π, so Wikipedia should not do original research and express it differently. Dirac66 (talk) 03:25, 19 February 2015 (UTC)

Seeing this discussion I think more details on the connection between rotational spectroscopy levels and nuclear spins should be specified.--193.231.19.53 (talk) 09:40, 20 February 2015 (UTC)

Concerning the arithmetic point of integer multiples of h/4π one logical consequence arises: integer multiples of h/2π (ħ) as the nuclear spin of N-14 are also integer multiples of h/4π, but not all integer multiples of h/4π are integer multiples of h/2π. In this way the objection based on N-14 spin has lesser ground. This arithmetic translation/change of variables should not be considered WP:OR, but just a trivial mathematical operation frequently encountered in science seminars. I think what is allowed in science books and seminars where some derivation are left as exercises can be allowed also here on Wikipedia because this is a natural procedure that should not be hindered by an artificial and hasty/superficial application of a wikirule.--193.231.19.53 (talk) 10:02, 20 February 2015 (UTC)

I think that statement about multiple integers of h/2π and h/4π needs a formula to be more illustrative.

$n\hbar =2n{\frac {\hbar }{2}}$--86.125.191.52 (talk) 15:18, 23 February 2015 (UTC)

There is no logical significance to the choice of units. There is no consequence of the nature you suggest: that "In this way the objection based on N-14 spin has lesser ground." (Agreed that calling it OR is not really appropriate, but it is a nonstandard way of expressing it, and there is nothing to be gained by doing so.) —Quondum 18:10, 20 February 2015 (UTC)

The choice of ħ/2 instead of ħ makes both spin angular momentum numbers integers and the distinction half integer vs integer disappears.--86.125.191.52 (talk) 15:25, 23 February 2015 (UTC)

It doesn't disappear, it just gets (hypothetically) renamed to "odd integer" vs. "even integer". The distinction between fermions and bosons remains fundamental to particle physics no matter how you choose your units. --Ørjan (talk) 10:07, 24 February 2015 (UTC)

I notice that there is a discussion about consequences of N-14 spin inferred from experimental data. More details should be added. I'll open a subsection here involving Franco Rasetti's results.--79.119.213.43 (talk) 17:39, 21 February 2015 (UTC)

It seems that N-14 spin measurement by Rasetti involves spin isomers similar to the case of H2. Spin isomers exist not only in the case of hydrogen as someone might have the impression.--86.125.191.52 (talk) 15:32, 23 February 2015 (UTC)

The nuclear spin (of hydrogen) is also connected to the specific heat (of hydrogen), as pointed out by D.M. Denison (1928) and presented by Tomonaga in The Story of Spin. Other aspects and references are mentioned on de.wp in its article about spin from which I quote some text : D.M.Dennison: A Note on the Specific Heat of the Hydrogen Molecule. In: Proceedings of the Royal Society of London Series A. Bd. 115, 1927, S. 483–486. Warum ausgerechnet eine makroskopisch messbare Eigenschaft des H2-Moleküls zum Spin der Atomkerne führt [the connection between macroscopically measurable property of H2 and nuclear spin], ist ausführlich beschrieben [is further described] in Jörn Bleck-Neuhaus: Elementare Teilchen. Moderne Physik von den Atomen bis zum Standard-Modell Kap. 7. Springer-Verlag 2010, ISBN=978-3-540-85299-5--5.15.49.164 (talk) 21:11, 23 February 2015 (UTC)

Relevant chapters/lectures from Tomonaga's Story of Spin: chp 4 Proton Spin p 63-78 and chp 8 Spin and Statistics of Elementary Particles p 131-150. Additionally, chp 9 The Year of Discovery 1932 p 150-162.--5.15.49.164 (talk) 21:54, 23 February 2015 (UTC)

Franco Rasetti

The discussion in this section of this talk page involves experimental results on N-14 obtained by Franco Rasetti. I have opened this sub-section.--79.119.213.43 (talk) 17:42, 21 February 2015 (UTC)

A. Pais's book Inward Bound has a discussion on pp. 299-302. The spin issue was discovered by Kronig in 1928. Rasetti worked on nuclear statistics through the Raman effect a year later. Consistent with Kronig's argument, Rasetti found "wrong" nuclear statistics for N_2 a year later, as evidenced by the hyperfine structure measurements (writing what Pais has to say). Attributing the N-14 spin argument to Rasetti is not correct; as Pais notes, Kronig could have deduced the statistics paradox. That discussion should be in the section above, where this issue is introduced. Bdushaw (talk) 02:43, 23 February 2015 (UTC)

What do you mean by Kronig could have deduced? Many scientists could have deduced some conclusion but in fact did not. The article on Rasetti now gives credit to Gerhard Herzberg and Walter Heitler using Rasetti's spectrum. Is this incorrect? Dirac66 (talk) 03:07, 23 February 2015 (UTC)

Just to reiterate, I am just working from the narrative from the Pais book. Kronig had the basic argument concerning the spins and 14+7=21 requires spin 1/2, which N14 was not. The Rasetti argument was essentially the same result, just from the hyperfine structure point of view. Since Kronig had the more basic result, if he had thought of the hyperfine structure problem, he would have been able to predict what Rasetti found. (would have, could have, as you say). They were both on the same track. This article, the neutron, has it about right: we have a paragraph on 14+7=21, followed by a paragraph on hyperfine structure. I believe Kronig goes to the former (1928), Rasetti (with Herzberg and Heitler) the latter (1929). I could be wrong about it, however. But assigning Rasetti to the former is not quite right, seems to me.

Thinking about this question, I am wondering if we want to start describing the history at this level here - do we want to give "who did what" everywhere? Is that relevant/necessary to this article on the neutron? Something for us all to sort out. My neighbor took a look at the article and his one comment was "its really long". I wonder if perhaps the history sections (or other parts similarly) should be broken out into a separate article on the history of the neutron, replacing it with a brief summary paragraph or two. That history does serve as an introduction to the nature of the neutron. I contemplate writing more material on the "valley of stability" as discussed above, and the lower sections of this article do need development/polishing. Bdushaw (talk) 06:13, 23 February 2015 (UTC)

An article titled Proof of the neutron structure would be fine.--5.15.49.164 (talk) 21:19, 23 February 2015 (UTC)

The historical detail is useful to underline the demonstration of the constituency of the neutron (proton-electron or not). Omitting relevant (historical) detail is omitting steps in the proof of rejecting the proton-electron hypothesis. Omissions of essential steps gives the impression of non-convincing rejection of proton-electron structure based on non very scientific criteria. Of course a separate article on the history of the neutron or other parts could be made. Also details on the valley of stability are useful. Other topics like the consequences of neutron structure models on the theory of beta decay could be also emphasized.--5.15.188.131 (talk) 09:29, 23 February 2015 (UTC)

It must be underlined that the dichotomy Kronig vs Rasetti is a false one because complementary aspects are involved, theoretical (Kronig) and experimental (Rassetti).--5.15.188.131 (talk) 09:35, 23 February 2015 (UTC)

The intrinsic conceptual connections should be clearly presented/emphasized.--5.15.188.131 (talk) 09:45, 23 February 2015 (UTC)

There were various theoretical objections to the p-e model floating around at the time including the uncertainty principle which today seems the most obvious one, as it implies that electrons cannot be confined to the nucleus. However without experimental evidence physicists were uncertain as to how seriously to take the objections (Kronig as well as Heisenberg) and which theoretical ideas to retain (some were rejected such as Bohr's idea that energy is not conserved in beta-decay), so it is important to explain the work of Rasetti which was very early experimental evidence against the p-e model.

And I agree that the history section should be broken out into a separate article named Discovery of the neutron. This is a better title than History of the neutron since the article would be restricted to the discovery period (roughly 1928-34) and exclude later developments such as quarks. If the Discovery section becomes a separate article, then this Neutron article could just briefly mention the p-e model and say that it was discarded since the p-n model better explained the experimental data, with a link to the new article of course. Dirac66 (talk) 00:43, 24 February 2015 (UTC)

The uncertainty relation is not a very serious objection who can't be dealt with (and it has mentioned somewhere above/before on this talk page). Even Heisenberg considered the possibility that uncertainty relation is/was not applicable in nuclei. The source by H. Schopper on beta-decay says on page 1 that the kinetic energy required by the uncertainty relation needs to be balanced by an attractive interaction. The way from brute experimental (spectroscopic) data which are ambivalent to inference based on it/them is pretty convoluted and involves some working hypotheses or assumptions whose validity is not always beyond reasonable alternatives. An example involved here is the identification of neutron and proton spin based on spectroscopic data. The conclusion that experimental data of Rasetti and other was/is an early experimental evidence against p-e is not very straightforward.--5.15.15.156 (talk) 08:34, 24 February 2015 (UTC)

A possible title of a separate article can be Developments on neutron structure which can include both the discovery and modern developments.--5.15.15.156 (talk) 08:54, 24 February 2015 (UTC)

Electron-proton association to form neutrons only possible if neutrino emitted

According to an edit today by 5.15.49.164, This experimental data [i.e. spin of ¹⁴N = integer] was consistent with no individual or standalone electrons in nuclei and did not exclude the possibility of electrons associating with protons to form neutrons. In fact the integer spin of ¹⁴N does exclude a simple p + e → n association of the type envisaged by Rutherford, since the quantum-mechanical addition of spin 1/2 for the proton and spin 1/2 for the electron must give a resultant (neutron) spin of either 1 or 0. So we would have a ¹⁴N nucleus of 7 protons (spin 1/2) plus 7 Rutherford neutrons (spin 1 or 0) and an overall spin which is half-integral, contrary to the experimental result.

This problem was resolved a few years later by Fermi, who proposed that the p-e reaction also involves neutrino emission: p + e → n + ν. The neutrino has spin 1/2 so the neutron is left with spin 1/2 also and the ¹⁴N spin is integral as per experiment. Also as noted elsewhere, the neutrino carries away the missing energy and solves the energy-conservation problem.

However as pointed out above, the neutron discovery section is already too long and should probably become a separate article. So I will not try to explain all this here - instead I will just delete the incorrect statement. Dirac66 (talk) 03:59, 24 February 2015 (UTC)

The Fermi proposal involving spins was very speculative in absence of neutrino detection about 20 years later and I have addressed the issues on spin in a section above. Its conditions can be compared with those of the hydrogen atom also a proton-electron combination. Rutherford conceived the neutron as a collapsed hydrogen atom. The possibility of a proton-electron association has not a straightforward status of an incorrect statement, there are reasonable alternatives.--5.15.15.156 (talk) 08:47, 24 February 2015 (UTC)

This source [8] discuss the conditions of proton-electron association to generate neutrons.--5.15.7.103 (talk) 07:20, 18 March 2015 (UTC)

Accelerators for neutron beams

How can a beam of neutron be accelerated, considering the neutral charge of the neutron? It should be specified in article.--193.231.19.53 (talk) 12:05, 3 March 2015 (UTC)

This question is answered briefly in the section Neutron#Neutron beams and modification of beams after production. Dirac66 (talk) 20:33, 3 March 2015 (UTC)

New "Discovery of the Neutron" article

Just to start a stub for a discussion on if/how to break the history section into a separate article. I tend to be in favor of the idea, since the lengthy history section seems to be detracting from the main article on the neutron itself, which continues to need work. We should perhaps have a bit more discussion of the idea: Are all agreed? How to develop the new article? What small couple of paragraphs to hit the basic highlights of the neutron history? The article James Chadwick has other contributions that might be useful to call a reader's attention to.

I suppose I just contemplate cutting and pasting the history section into a new article, and then leaving both for a time. Then after "a time" removing the history section from this article, leaving a couple of paragraphs with "Main article" and "See Also" highlights.

Splitting the article is with some regret, since this history section is in many ways a nice introduction into the neutron itself.

(As an aside, I've developed the Neutron magnetic moment article a bit more to describe how people tried to explain the neutron's magnetic moment from 1935-1965. This question was asked towards the top of this talk page.) Bdushaw (talk) 03:30, 20 March 2015 (UTC)

(The talk page is also a bit overdue for an archive action) Bdushaw (talk) 03:31, 20 March 2015 (UTC)

I support a split. Isn't this how articles develop? A short history section to remain would still serve as a brief introduction. The detail of the history with all its twists and turns makes for interesting reading, but that really does deserve its own article. —Quondum 04:08, 20 March 2015 (UTC)

Yes, I agree. Just to be clear, the new article would be named "Discovery of the Neutron", but its content should correspond to the entire section now named 2.Discovery, and not just to the subsection now named 2.3 Discovery of the neutron. Dirac66 (talk) 11:58, 20 March 2015 (UTC)

I've copied over the bulk of the Discovery sections to Discovery of the neutron. I'll pause for a day or two before attempting to condense/delete these sections on this page (unless someone gets to it first). I think we are agreed that perhaps just 1-2 short summary paragraphs should remain on this page. The figure in this Discovery page of the composition of sundry nuclei should likely remain. Meanwhile, on the Discovery page, I feel the liberty to now include photos of Rutherford, Chadwick, etc. I was worried about how the references would transfer over, but there were just a couple of corrections needed. Bdushaw (talk) 22:28, 21 March 2015 (UTC)

OK, looks generally good. For the summary on this page, I think we should retain a mention (say one sentence) of the proton-electron model so that all readers are notified that it once existed. Those who want more details will then know to go to the new article. Dirac66 (talk) 23:18, 21 March 2015 (UTC)

I am trying to proceed slowly and deliberately for comments such as this and to avoid errors that may be difficult to correct later. The new article has a speedy delete claim from copyright infringement, which I find annoying. Many external pages have copied wholesale from Wikipedia, which can make it difficult to avoid self-references. One of the External Links added not too long ago goes to a page that is mainly copied from this article. This is the nature of Wikipedia, I gather, but external sites should be more careful to acknowledge their material came from Wikipedia. One hopes Wikipedia has various legal recourse to ensure legalities are respected. Bdushaw (talk) 23:51, 21 March 2015 (UTC)

O.K., I hacked the Discovery section back a long ways. Perhaps further condensation is possible; pretty easy to make errors doing this. I tried to retain the citations. Pausing again. Bdushaw (talk) 21:57, 22 March 2015 (UTC)