Talk:Neutron/Archive 4

Archive 1

Archive 2

Archive 3

Archive 4

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)

The issue here (revisited) is characterized by the nuclear drip line - neutrons or protons are emitted for those nuclides that sit on the outer boundaries of the "valley of nuclear stability". We do not see protons emitted so often because we do not see nuclides that are so proton rich, usually. There needs to be an article on the Valley of nuclear stability. (I've been poking at the article on beta decay recently.) Bdushaw (talk) 19:39, 8 June 2016 (UTC)

We have the article Island of stability, which is the same thing with sign reversed: the variable is considered to be stability rather than potential energy. Perhaps we could place a redirect at Valley of (nuclear) stability to Island of stability. Dirac66 (talk) 02:54, 9 June 2016 (UTC)

Ah, but they are not the same thing - I got confused by that too. The island of stability is a conjecture (?) that there is a small region within the upper reaches of the valley of stability where very heavy nuclei will be stable (if I understand it correctly). An article on valley of stability would bring together articles on neutron, proton, nuclide, beta decay, drip lines, island of stability, etc., and, besides, it is a well-documented concept. (I'm not actually arguing FOR this article just yet, just sorting through what makes most sense.) Bdushaw (talk) 09:43, 9 June 2016 (UTC)

Archive of talk page

I've archived this Talk page, as you see, since this seemed a good place/time to do that. Much of the existing discussion was old or related to the Discovery of the Neutron sections, which are now a different article. The section above relates to the Valley of Beta Stability, which I think needs a bit of development in the article (to explain why neutrons, rather than protons, get released during the fission process.) Dearchive other sections as desired, perhaps retaining the chronological order. Bdushaw (talk) 19:43, 9 April 2015 (UTC)

Not vandalism

You do not need to undo my contributions. They are not vandalism. I have added in the last days a few addenda which are all correct. Bfaster (talk) 02:56, 29 November 2015 (UTC)

About the caption for the models depicting the nucleus and electron energy levels in hydrogen, helium, lithium, and neon atoms

The caption for the models depicting the nucleus and electron energy levels in hydrogen, helium, lithium, and neon atoms, says that the second and the third energy levels can each contain up to 8 electrons what i think it's not true for the second level. Thank You. Dorivaldo de C. M. dos Santos (talk) 09:07, 22 February 2016 (UTC)

The nth level can contain up to 2n² electrons, but in any case the outermost level can contain at most 8 (see this source). So in this case, the second level has up to 2 2^2 = 8, and the third level, which normally can have 2 3^2 = 18, has, when being the outermost, up to 8 too. See also article Electron shell- DVdm (talk) 09:40, 22 February 2016 (UTC)

Also the caption confuses levels and shells. A more correct statement would be that the second shell (n = 2) corresponds to two levels (2s, 2p) which can contain up to 8 electrons. The n = 3 shell has three levels (3s, 3p, 3d) which can contain up to 18 electrons, but 3d is occupied after 4s so that yes, there will be only more than 8 electrons in n = 3 when 4s is occupied so that n = 3 is not the outermost shell.

However this is all much too complicated for one figure caption in an article about the Neutron. For this article, I would recommend redrawing the figure to just show the numbers of protons, neutrons and electrons without mentioning electron energy levels. Dirac66 (talk) 19:11, 24 February 2016 (UTC)

Electric Polarizability Source

I noticed that the neutron electric polarizability value in the sidebar does not have a citation associated with it. Also, it is outside the bounds of the measurements that I have encountered (see this source). Where did this value come from? I checked CODATA and it doesn't have a value for it. — Preceding unsigned comment added by 129.79.152.123 (talk) 19:18, 23 February 2016 (UTC)

Valley of stability article

As a consequence of some of the discussion above, I have been working recently on the new article Valley of stability. I fussed with the issue for quite some time before coming to the conclusion that such an article is required. The article resolved some problems with redirects, and it, in my view, synthesizes a variety of articles that would otherwise be disparate. The motivation originated with the puzzle as to why neutrons are scattered about in fission, but not protons - the discussion above shows that the reason is apparent with the valley of stability in mind. Also the question of why nuclear reactors have an intense flux of antineutrinos from beta- decay is explained (fission products are neutron rich). In any case, I've been writing the article as a non-expert, so I post this notice here to invite some review of the new valley article. There are still some missing pieces, but one can at least see what I have in mind; I've been working from the sources cited. Thx, Bdushaw (talk) 21:17, 23 July 2016 (UTC)

Template:Commons category

Wikimedia Commons has media related to Neutron, but links - https://commons.wikimedia.org/wiki/Category:peneutron (This page does not currently exist) --Fractaler 07:15, 28 November 2016 (UTC) — Preceding unsigned comment added by Fractaler (talk • contribs)

Fixed, there was a vandal edit on Wikidata. --Ørjan (talk) 06:57, 29 November 2016 (UTC)

Discrepancy in lifetime measurement

recent article http://fermatslibrary.com/s/the-neutron-enigma describes there are two separate methods for measuring the free neutron lifetime, and they are both accurate, but differ by almost 1%. This indicates there is unknown physics at work. While this page does mention that the lifetime uncertainty, it's not mentioned that it's degree of uncertainty is very high and still interesting to physicists. 216.252.162.16 (talk) 06:15, 26 April 2017 (UTC)

A, Z, N in lede

I've been thinking about the recent changes to the lede regarding definitions of A, Z, N. I am unsure quite what to do - I have sympathy for shortening/simplifying the lede, while, on the other hand, in the nucleus A, Z, N are fairly critical to what a neutron is. I was just thinking that perhaps some of the sentences recently removed (e.g., a neutron is not an element, but it is included in Segre chart) might be moved to the first paragraph of the discussion section. Dirac's recent change remedies the issue a little bit, but there still seem to me to be issues. We might introduce A, Z, N in the first paragraph of lede, and rely on the Discussion section to provide the more thorough, well, discussion. Meanwhile, I spent quite a lot of time fussing with the lede, hence considered it perfect before, hence tend to dispute any changes at all in my mind...hence I fight the tendency to leap in to object to changes... Bdushaw (talk) 16:40, 7 August 2017 (UTC)

Discussion section?? Do you mean Description section? Dirac66 (talk) 18:53, 7 August 2017 (UTC)

Oops, yes Description section. (I am writing something else at the moment that has a Discussion section.) Bdushaw (talk) 19:15, 7 August 2017 (UTC)

I have cobbled together a revision based on the original state of things, but addressing the points of simplifying the lede. I thought that some of the deleted information was actually important, so I shifted it down to Description. See what you think; edit as desired! Bdushaw (talk) 15:16, 12 August 2017 (UTC)

I like your version a lot. Good work. Power~enwiki (talk) 15:49, 12 August 2017 (UTC)

Yes, I think it is good now. I will only criticize the change to the Mass section, which I realize was not your primary concern. In the phrase mass of protons and deuterons, the use of the singular mass could imply to an innocent reader that a proton and a deuteron have equal masses!?? I will change it back to masses. Dirac66 (talk) 18:46, 12 August 2017 (UTC)

Discovery again

Just to note that for several reasons I have been developing the Discovery of the neutron page again. Mainly filling in some important discussions connecting the Rutherford gold foil experiment to the Rutherford model for the atom - the work with isotopes seems to me to be an important part of the story. There is a "clarification needed" noted in the section below under binding energy, which can now be answered. There is one more missing element, which is Moseley's work on atomic number, Z, but I'll save that for a rainy day. I'm not sure if everyone is monitoring the changes to that page, but happy to have others take a look at what I've done there. Discussions should be on the Talk Page for that article. Bdushaw (talk) 16:19, 20 August 2017 (UTC)

Description section finale

I must say the several sentences at the end of the Description section have been editted so that they seem to be rather drifting off the rails... The Standard Model and its complexities are rather, well, complex. To give a clear explanation of the effects and consequences of the strong force here would take us rather far afhaield...and rather lengthen the article! "particle's Standard Model" is incorrect, I believe. Bdushaw (talk) 03:31, 3 October 2017 (UTC)

Dukwon has now removed one sentence fragment and I have removed another sentence. Also, I added a link for secondary effects of the strong force, and removed the invitation to explain the point in this article. I think the last 2 remaining paragraphs in the section are now at an appropriate level. Dirac66 (talk) 14:45, 3 October 2017 (UTC)

The chemical and nuclear properties of the nucleus

I don't like "The chemical and nuclear properties of the nucleus are determined by the number of protons". The nucleus has no direct chemical properties and the nuclear properties are equally dependent on both the protons and neutrons. I propose a edit saying that the chemical properties are determined by the number of electrons which is determined by the number of protons and to make it explicit that both protons and neutrons are equally important for nuclear properties and that neutrons have almost no effect on chemistry. I think it is important to make it clear that nuclear properties can be very different despite almost identical chemical properties and neutrons are the key to this difference. Exact wording is TBD but as this is a top paragraph of a prominent article I thought I would comment on it here first just incase anyone has strong views. Mtpaley (talk) 00:34, 23 January 2018 (UTC)

"Unineutron" listed at Redirects for discussion

An editor has asked for a discussion to address the redirect Unineutron. Please participate in the redirect discussion if you wish to do so. –LaundryPizza03 (dc̄) 07:15, 25 April 2020 (UTC)

Sentence in lede

Its always good to re-review articles... In the lede, I noticed the phrase: The chemical and nuclear properties of the nucleus are determined by the number of..., which strikes me as odd (though I may have written it...). Firstly, nuclei do not have chemical properties, secondly "nuclear properties of the nucleus" sounds redundant. I am thinking that just The properties of nuclei are determined by the number of... may be better, perhaps including a separate sentence to indicate that the number of protons determines the chemical characteristics of the associated atom. At this point, I thought it might be better to post this for discussion. Bdushaw (talk) 08:16, 23 May 2020 (UTC)

Just noticed Mtpaley's complaint about this sentence above, dated 2 years ago... Bdushaw (talk) 08:27, 23 May 2020 (UTC)

I have now rewritten the offending sentences as two separate sentences - one for chemical properties and one for nuclear properties. Plus a third sentence using C-12 and C-13 as an example. Dirac66 (talk) 02:28, 25 May 2020 (UTC)

I gave it a bit of polish. I seem to recall that someone went through that paragraph revising and removing what they thought was non-essential discussion. It seems to me this paragraph is a bit "in for an penny, in for a pound" in that to get to the discussion of what a neutron is, the other various elements of the atom have to be described. I keep the poor 8th grader in mind; he needs to know the basic facts. I note that the lede should reflect what is in the text, hence the next needs an equivalent discussion. Let's get the lede wording right first. Bdushaw (talk) 08:11, 25 May 2020 (UTC)

One option would be to delete the 2nd and 3rd paragraphs of this latest revision entirely (chemical properties, isotopes). Then proceed with nuclear properties as 2nd paragraph, nuclear charge, weight, etc. The issue is how focused should the lede be specifically on the neutron itself, vs the larger context of the neutron within the atom? Bdushaw (talk) 10:05, 25 May 2020 (UTC)

Another odd sentence in the lede is Free neutrons, while not directly ionizing atoms, cause ionizing radiation I am not sure what is meant by that - but I think the idea is free neutrons decay into energetic particles that are ionizing (p,e, nu). Perhaps the sentence should be revised to say that? Free neutrons decay, rather than "cause ionizing radiation"? Bdushaw (talk) 21:10, 26 May 2020 (UTC)

Two comments on the latest version of the intro: 1."The number of electrons is determined by the charge of the nucleus...". This is true for neutral atoms but not for ions. We could say "The number of electrons of a neutral atom is determined by the charge of the nucleus" or else "The number of electrons is determined by the charge of the nucleus and by the net charge of the atom (or ion)". 2."To a lesser extent, chemical properties are influenced by the mass of the nucleus,..." This appears to be a reference to the kinetic isotope effect which is a very advanced topic. As you said above, the poor 8th grader needs to know the basic facts about neutrons, and s/he would find no indication at all in this article or in a high-school textbook about why chemical properties should be influenced by the mass of the nucleus. Given the level of the article and the intro, I would suggest just leaving out the isotope effect and saying that the chemical properties are determined by the electron configuration and the nuclear charge, which is qualitatively true. Dirac66 (talk) 19:37, 27 May 2020 (UTC)

The isotope effect is major for hydrogen and minor for everybody else. So I think that if we are going to talk about this, we need to make it very clear that it is usually negligible. Double sharp (talk) 04:44, 28 May 2020 (UTC)

The points above are well taken, and I was indeed contemplating heavy water as I wrote those paragraphs. (I had recalled that drinking a glass of heavy water would kill you, but that turns out not to be true.) But we can avoid "number of electrons", which is just a problem, and avoid the isotope effect, while being accurate, I think. The problem with paragraphs like this is that when you say "This is true." Someone will point out that "yes but 1% of the time THAT is true" so what about THAT! In this case the isotope effect seems to be a matter of "undue weight." Anyways, I have a revision in mind that may address the above concerns. Thx! Bdushaw (talk) 09:38, 28 May 2020 (UTC)

I suppose a simple way to describe the isotope effect is to say simply that the same reactions occur but at slightly different rates. The words "different rates" could be linked to the article on kinetic isotope effect. Dirac66 (talk) 09:56, 28 May 2020 (UTC) However I see that the mention of mass effects on chemical properties has now been deleted. This is probably better. Dirac66 (talk) 10:41, 28 May 2020 (UTC)

I am just recalling that the neutron DOES affect the electronic configuration...through its magnetic moment, it affects the hyperfine structure of atomic spectra. That's a tiny effect...perhaps we may ignore it in the lede...Bdushaw (talk) 09:51, 29 May 2020 (UTC)

I've thought about hedging the lede wordage a bit to account for hyperfine structure, but I think it is OK as it is. Regarding free neutrons causing an ionization hazard, further reading indicates that this occurs by, e.g., neutron absorption, causing subsequent nuclear instability and decay. Not so much from the decay of the neutron itself, though that can happen too, I am sure. In short, I think the vague language is OK given the complicated story behind this. Bdushaw (talk) 09:11, 30 May 2020 (UTC)

I think the lede should be kept simple. Some of these more advanced or more minor points could be placed in new sections further down in the article, but not in the lede. Dirac66 (talk) 11:56, 30 May 2020 (UTC)

beta decay / standard model

I did a bit of reorganization and development. The original paragraph on the Standard Model was just out of place and has always bothered me. The changes required a bit of development, which is always dangerous since it has to respect the article as a whole. There is a bit of repetition at the moment which seems OK. Feel free to revert/correct/etc. There is room now to develop the standard model decay description, if needed. Bdushaw (talk) 16:44, 4 June 2020 (UTC)

First use of "neutron"?

This sentence has appeared in the "History" section: The American chemist W.D. Harkins correctly predicted the existence of the neutron in 1920 (as a proton–electron complex) and was the first to use the word "neutron" in connection with the atomic nucleus. with citations. That may or may not be true, but the sentence appears just after the discussion of Rutherford describing neutrons, and using the word neutron, in 1920. The sentence appears to be in the "wrong" place (now starting off the paragraph on how the neutron was seen as composite). Not sure how to reconcile, but seems to me the sentence sentiments could perhaps be meshed in with the Rutherford discussion above. Norman Feather gave perhaps the best history of where "neutron" came from. The situation is likely that at this time the idea was floating around generally - though it was certainly not generally known! See the "Discovery" main article. Bdushaw (talk) 15:26, 23 January 2022 (UTC)

The article Discovery of the neutron says that "References to the word neutron in connection with the atom can be found in the literature as early as 1899." However since that preceded the discovery of a nucleus much smaller than the atom, I presume that the meaning of "neutron" in 1899 was quite different from the concept of Harkins and Rutherford proposed in 1920. Dirac66 (talk) 01:14, 11 February 2022 (UTC)

Sure RE 1899, but we seem to have conflicting citations regarding 1920. This article presently states that Rutherford was the first to use "neutron" in 1920. Then, in the next paragraph, it states that Harkins was the first to use "neutron" in 1920. I suspect this is a case of the word generally floating around about this time, though not generally known (c.f. the Curies in Paris were unaware of it). As presently written this article is...well, idiotic, is the word that comes to mind; careless, maybe. The Harkins statement is in the wrong place; it was added thoughtlessly - rather it should be merged in the paragraph above with something like "in 1920 the word neutron was independently introduced by Rutherford and Harkins..." or something like that; I was unaware (and am unaware) of the Harkins discussion; my instinct is to stick with Rutherford - there are all manner of claims as to who did what first in this subject! I specifically bought the book by Gamow (1931), perhaps the first monograph on nuclear physics, and was amazed there was no mention at all of neutron in it (Gamow was in Copenhagen at that time). Obviously no one had an impact with "neutron" in 1920, other than on Rutherford and Chadwick who looked for it over the ensuing decade (no one else did, that I know of; I doubt they were motivated by Harkins...). Bdushaw (talk) 15:58, 18 February 2022 (UTC)

Looking at the citations again...the Harkins citation is actually 1921, whereas Rutherford's "neutron" was his Royal Society lecture and paper in 1920, a famous lecture/paper. My own inclination, again, is to rule out Harkins. (Linus Pauling citaton notwithstanding) Bdushaw (talk) 16:03, 18 February 2022 (UTC)

I also see from the Harkins paper (first page) that it was communicated by Rutherford...I think the notion that Harkins was first with neutron is all wet... Bdushaw (talk) 16:14, 18 February 2022 (UTC)

Well, Feather (1960) supports Harkins (1921) as using the word "neutron" for the first time: "In the first of these papers [1921] he [Harkins] used the word 'neutron' for the first time". I think that is definitive. Both Rutherford and Harkins (and others) were generally contemplating such a particle as a hydrogen nucleus closely bound to an electron at this time. Rutherford was unique in speculating on its properties, with an eye on how such a particle might be detected. But Harkins used the word first. I would suggest revising this article to respect Rutherford's Bakerian Lecture discussion ("neutron" NOT used), while acknowledging Harkin's neutron dating to 1921, citing his 1921 article and Feather (1960) (we can remove the Pauling (1970) citation,IMO). Both Feather and Stuewer comment on how confusing the various contributions were at this time; quite a lot of speculating going on; difficult to discern who did what first. In any case "neutron" did not catch on until 1932... Bdushaw (talk) 16:53, 18 February 2022 (UTC)

There is a copy of Rutherford's Bakerian lecture at https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1920.0040. The word "neutron" is absent, but on page 396 he proposes that "Under some conditions, however, it may be possible for an electron to com­bine much more closely with the H nucleus, forming a kind of neutral doublet." This sounds to me like a proton-electron complex with a different name. I have not seen Harkins' 1921 paper, but perhaps he took Rutherford's proposal and added the word "neutron". So I suggest (subject to further verification) that Rutherford gets the credit for the concept of a neutron in the nucleus, but Harkins perhaps gets the credit for calling it a neutron. Dirac66 (talk) 03:18, 19 February 2022 (UTC)

Yes, that seems to be the case - the quote you give, including the subsequent text on what an elusive particle it would be, is fairly famous. Meanwhile, curious fact, it appears that Rutherford is "communicating" all these papers (recommending them to the journal?), even adding a footnote to one of them. It doesn't take much imagination to think that Rutherford suggested to Harkins that he use the name, but that's straying. I saw that the Byrne citation/book also notes that Harkins used "neutron" first. The text added regarding Harkins uses he "correctly predicted", but that's too strong a language. There were a few papers on the subject appearing all about the same time, but all being more of a speculative nature; Rutherford was unique in suggesting avenues for experimental detection in the laboratory. Bdushaw (talk) 12:15, 19 February 2022 (UTC)

I've made a revision; I had to bear in mind that the text should be brief, since the extensive discussion is given in the Discovery article. Bdushaw (talk) 12:35, 19 February 2022 (UTC)

New Neutron Lifetime Measurement

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.162501 τ_n = 877.75±0.28_stat +0.22/-0.16_sys s Abyssoft (talk) 07:47, 19 February 2022 (UTC)

New "Mass ratio" section

The section stating that ratio of the mass of the neutron to that of the electron can be derived theoretically seems odd. I can see no physical relation between the two. The citation given seems odd as well, not a conventional citation. Perhaps this (new) section ought to be removed? Or a more conventional citation found for it. Even if true, I question the inclusion/value of this esoteric formula, without a brief physical discussion as to why the two masses should be related. Bdushaw (talk) 06:47, 22 May 2022 (UTC)

Good catch. Complete nonsense like that shouldn't have survived two months. --mfb (talk) 11:20, 5 June 2022 (UTC)

Yes. To see who this material is coming from, I took the trouble of looking up the article about the author of the cited source and his company: see Randell Mills. Total revision of modern quantum physics, without any experimental evidence of course. I agree with the deletion from this article. Dirac66 (talk) 17:19, 5 June 2022 (UTC)

What is the mass of a neutron

Not sure how to work this question out would be nice for help and a understandable discussion about this thanks 82.43.130.181 (talk) 01:48, 28 September 2022 (UTC)

See Section 5 Intrinsic properties, subsection 5.1 Mass. Do you have a question which is not answered there? Dirac66 (talk) 12:14, 28 September 2022 (UTC)

2 Questions

1. The article states:" Protons can decay to neutrons, or vice versa, within the nucleus. This process, called beta decay, requires the emission of an electron or positron and an associated neutrino." This needs work. The "or" is doing way, way too much work here. So, a proton can "decay" into a neutron with the emission of an electron? A proton can decay into a neutron with the emission of a positron? Is that "and a neutrino" (remove the "associated", for goodness sake, it adds nothing!) for both of those decays? I think it needs a reference - as well as mention that it doesn't happen often (relative to neutron to proton decay). I also think that the last should be first, that is the sentence should be:"Within the nucleus, neutrons can decay to protons, or vice versa." Since unquestionably this is the more common transformation.

2. It also states:"But a high-energy collision of a proton and an electron or neutrino can result in a neutron.". Again the "or". I really doubt that there is any meaning to the term "high-energy collision" when referring to proton+neutrino interactions. Isn't the energy of the neutrino, relative to the proton, pretty much constant (it's rest mass)? Also, I'm sure that charge conservation isn't violated, so if it is true that a proton and neutrino can produce a neutron, (without an electron) then a positron would ALSO have to result (and should be mentioned).

3. I was taught, long, long ago, that neutrons were "made" of a proton, an electron, and a neutrino. We now 'know' that it is composed of 3 quarks, as is the proton. What I'd like to see a discussion of is the way a proton can emit a positron (and a neutrino?) and transform along with the electron (of the electron/positron virtual pair) into a neutron. But about that neutrino. Both electrons and neutrinos are fundamental, so how is it possible (IS it possible) for them to be created or destroyed as single particles (not pairs with opposing momentum)?174.130.71.156 (talk) 02:30, 25 December 2022 (UTC)

A quick reply, perhaps more later and others can comment. The statements from the article in question 1,2 should likely be clarified. The statements are meant to refer and introduce, generally, to beta decay generally. So the language does play rather fast and loose with electron/positron and anti-neutrino/neutrino, etc. "associated neutrino" is because it is either a neutrino or anti-neutrino. It would be better, perhaps, to spend the text and be specific about the n,p reactions. "high-energy neutrino" refers not to the mass of the neutrino, which is negligible, but the total energy, including kinetic, that it carries (reaction, e.g., n + nu -> p + e). RE: "neutrons were "made" of a proton, an electron, and a neutrino"...yeah, that's not correct. That's in the Fermi theory. The electron and neutrino are created at the moment of beta decay, much as photons are created at the moment of transitions of electrons in atomic energy levels. From the nuclear perspective we need not consider quarks, from the QCD perspective an up or down quark flips with the emission of electron and neutrino, etc. Lepton number conserved throughout. Bdushaw (talk) 11:29, 25 December 2022 (UTC)

I've made a revision, perhaps not answering all your concerns. In beta decay, a weak interaction, the corresponding particles are electron and antineutrino, or positron and neutrino. The decay starts with zero lepton number so the two leptons created have to have opposite lepton number. One makes choices in an article such as this, quite how deep one wants to go with the discussions; seems to me such a discussion of lepton number (leading to questions such as what is lepton number, why is it conserved, etc.) strays from the point of the article. And yes, citations needed all around; a rainy day project. Bdushaw (talk) 10:18, 27 December 2022 (UTC)

Gravitational mass

Under 'Intrinsic properties' it would be useful to mention the experiments to determine the behaviour of neutrons in a gravitational field.HuPi (talk) 14:59, 24 February 2023 (UTC)

Mistakes in the decay

The decay section has the terms mixed up. It should be talking about the neutron decaying to a proton and not vice-versa. 193.50.135.206 (talk) 15:01, 3 July 2023 (UTC)

As stated in the article, a *free* neutron decays to a proton (and not vice versa). However a *bound* neutron (inside a nucleus) can go either way: in some nuclei a neutron decays to a proton, but in others a proton decays to a neutron.

Perhaps it would be clearer for beginners if we mentioned the free neutron case first. Dirac66 (talk) 15:37, 3 July 2023 (UTC)

The situation is described already in "Description", and restated in the paragraph just above "Free neutron decay". I am not exactly sure what 193.50.135.206's objection is, but it seems to be the mistaken understanding that "protons do not decay" absolutely, which just isn't the case (within a nucleus). Perhaps that last paragraph ("Free" neutrons or protons are nucleons...) could be moved up to be the 2nd paragraph? (above Within the nucleus, neutrons...).Bdushaw (talk) 18:56, 4 July 2023 (UTC)

Good idea to start the section with free neutrons as that is the simpler case. So I have gone ahead and made the change. Dirac66 (talk) 02:51, 7 July 2023 (UTC)

Reverted last archive edit here, auto archiving enabled.

I moved the content of Archive/4 back. When the auto archiver runs tonight these older posts will again be archived, but 4 will remain to give context. Johnjbarton (talk) 17:31, 2 January 2024 (UTC)

Developing a "to do" list for this article

The article has been fairly stable lately (I've boldly archived what seemed like old and resolved discussions), but it seems there are still important tasks needed for the article. Perhaps we can communally make a list of what's still needed. (These first three items have nagged at me for years.) Bdushaw (talk) 12:26, 29 November 2023 (UTC)

• 1 Citations. The article often lacks citations for much of the discussion, and presently also includes citations in the lead. There is a lot of work needed to clean up the citations. These are often quite difficult, IMO - we've tried to write an article that introduces a complex topic in simple-to-understand language, and often finding a good citation for such simplifications is challenging. Even starting from an undergraduate text on Nuclear Physics would likely be overly complicated language. Nevertheless, citations needed.Bdushaw (talk) 12:26, 29 November 2023 (UTC)
• 2 Reconciling lead and text. Not a major task, but presently the lead involves material that has not been already included in the article itself. (e.g., Trinity Test, Chicago Pile)Bdushaw (talk) 12:26, 29 November 2023 (UTC)
• 3 I've mostly worked on the upper parts of the article. The parts further down regarding neutron sources and applications are out of my expertise. Those sections likely need a clean up. Indeed, I am wondering if perhaps this article ought to focus on just the neutron itself, and break out some of these sections into a new article on Neutron applications, say. Leaving a brief summary, much like the "Discovery" section was broken out.Bdushaw (talk) 12:26, 29 November 2023 (UTC)

  Completely agree about #1 and #2.

  Most sections the later half have existing articles, so rather than split, it makes more sense to me to move material out of this article and into the existing split-off ones. Make the sections more summary than mini-articles. I bet there are more split-off articles existing, eg I just linked Beta-decay.

  The "Description" section amounts to an extended lead; the entire article is a "description of the Neutron" right? The section could be a lower-level "Overview", but purpose of the section needs to be clarified.

  Having two decay sections is puzzling. There should be one, eg "Lifetime" or "Decay processes" section.

  "Intrinsic properties" should just be "Properties" and come before "Decay processes".

  The section on "Dineutrons" should be one sentence in "Properties". The 'Neutron compounds' section should be "Neutron stars" or "In neutron stars". Free dineutrons are barely notable but Neutron stars are a major aspect of neutron physics.

  There should be a section on neutron radiation hazards maybe as a rename of the odd "Protection" section.

  Good luck! Johnjbarton (talk) 15:34, 29 November 2023 (UTC)

Contemplating the article organization, I mostly agree with some of the suggestions by Johnjbarton. The "Description" section reads like an extended lead. The section "Beta decay and the stability of the nucleus" is really not about beta decay, but about how the neutron and proton build nuclei (with reference to beta decay) - the section wanders a bit. The section "Decay of the neutron by elementary particle physics" could really be "The neutron in the Standard Model" and include the quark discussion from "Description". I am not sure the lower sections (Neutron compounds and below) should be included/have such lengthy discussion. Should this article include a discussion on neutron detection?-(Philosophical question). Condense and farm out parts to other articles or new breakout articles? I am not entirely sure in how to proceed; I post this for comments/ideas. Bdushaw (talk) 20:07, 1 January 2024 (UTC)

First, I suggest leaving the intro work until it's clear what other changes make sense. Other changes might include moving material out of the intro. Once it is clear what the article will say, the intro can mirror it with brevity.

Second, references are important, so they should not be inadvertently deleted and purposeful deletions clearly described in the edit summary or Talk. Similarly any section without references are top priority for improvement.

Third, moving material from here into Main article if possible will improve both. If its just duplicate, then cut it here. I would avoid new breakout articles without building consensus: we have too many leaves and not enough sturdy branches. (Eg start a Talk item, explain why, and post it to the Physics talk for feed back.)

Fourth: just start.! If you make logical sized edits with descriptions, other editors can quickly revert if they don't agree and we can work it out.

Ok maybe you were looking for something more specific, but just start. For advice on a specific section, open a specific Talk topic. Johnjbarton (talk) 03:21, 2 January 2024 (UTC)

I noticed that you are "cutting" in one edit and "pasting" in another. It's much better if you can do this in one edit. Otherwise the edit history has large minus and large plus sized changes and that triggers bots and editors to check what goes on. Johnjbarton (talk) 15:35, 2 January 2024 (UTC)

Yes, I've run into trouble before as you say, but doing it this way is the only way I can keep track of things...it can get confusing in a hurry. I am careful to state what I am doing in the edit summary now to fend of mid-copy-paste reversions! Anyways, it has been a hatchet job so far of reformating/sketching a possible reorganization. Everyone should see how they like it - revert back to how it was if you are not happy with what I have in mind. Trying to get to a more conventional article format and organization. Not sure where to put "Discovery" - that might be better as a section further down in the article. Such large changes make a bit of a mess of the article, so more cleanup likely required. I've been able to remove quite a lot of redundancies so far. Stopping for now. Bdushaw (talk) 15:56, 2 January 2024 (UTC)

I hope to start working on improving the citations for the article in coming weeks. I still eye the lower half of the article - from Neutron compounds to temperature. I am not knowledgeable about these issues, but know enough to know these sections are bloated and disorganized...I may take a machete to these sections at some point, with the understanding, as mentioned above, that there will be no problem with reverting the hacks. For example, there is a (quite interesting) discussion of neutrons and their behavior on Mars that may or may not be warranted. It would be nice to bring this key article to "good article" status! Could it be possible? Bdushaw (talk) 10:31, 20 March 2024 (UTC)

It would be awesome if you moved most of the content in the "Neutron temperature" section to neutron temperature, leaving a single paragraph summary. Johnjbarton (talk) 15:42, 20 March 2024 (UTC)

The "free" neutron - half time

If the mean lifetime is 879.6±0.8 s then the half time is 609.7±0.7, not 610.1±0.7 s. Maybe this was caused by using "ln(2) = 0.693". Mc22222 (talk) 12:19, 29 March 2024 (UTC)

 Done thanks Johnjbarton (talk) 17:25, 29 March 2024 (UTC)

comment

I propose to change

... is possible because the mass of the neutron is slightly greater than that of the proton.

to

... is possible because the mass of the neutron is slightly greater than that of a proton-electron free pair. 151.29.78.113 (talk) 09:26, 28 March 2024 (UTC)

Sorry I don't think either of these phrases are correct. These imply that energy is the only consideration in decay processes, but that is not true.

I reworked the section but I'm not happy with the result. I think the decay is more complex than a few sentences can convey. The previous text was also trying to talk about the possible application of the decay energetics to neutrinos physics but again not enough was said to make it clear. Johnjbarton (talk) 16:00, 28 March 2024 (UTC)

I agree. I have just proposed to refine the necessary condition that was far too sloppy. Thanks and good Easter. 151.29.78.113 (talk) 06:24, 29 March 2024 (UTC)

It took me a moment to realize what the original poster was referring to - it is true that for the neutron to decay its energy/mass must be greater than not just the proton, but the energy/mass of the separate proton+electron+neutrino. I am not yet sure how to phrase that in the text; with somewhat of a worry of getting too bogged down in details. There are a multitude of caveats with physical facts, to stop and describe them all in an article is often counterproductive. (On a nuclear scale the mass of an electron seems tiny.) (One could also refer to a "bound" proton+electron, which would "decrease" their total mass with the binding energy, etc.) Bdushaw (talk) 10:14, 1 April 2024 (UTC)

A sentence on "free" proton decay

I restored the sentence noting that "free" proton decay is disallowed on grounds of energy. There are several concerns. Regarding "unsourced", I waive it away for now - as noted above, citations are generally needed, and hopefully will be provided this summer. The point may be "obvious", but, of course, "obvious" is in the mind of the beholder - it doesn't hurt to (re)state key points that may be obvious - our audience is general; some people will appreciate all the help we can give them. We have had 2-3 complaints on these Talk pages to the effect that "proton" decay does not occur, this with respect to the discussion further down regarding protons in the nucleus. A statement to this effect, acknowledging that "proton decay" does not occur, is therefore useful. Further, the reverted sentence serves as a lead in to that discussion further down regarding protons in the nucleus. Perhaps there is a better way to state the point (does it need its own paragraph?), but it seems important to retain an explicit statement of this fact. I am always open to convincing argument, however! Bdushaw (talk) 10:00, 1 April 2024 (UTC)

I think you could include a statement about the stability of products of the free neutron decay directly after describing those products. The stability of the products is physically significant (esp. regarding observing the products) whereas the "reverse reaction" is a made up thing.

For the purposes of the audience I think the energy carried away by the products is helpful to describe. The refs for neutron decay mention it, but they are advanced sources and what we need is something on the e=mc2 level. Johnjbarton (talk) 16:00, 1 April 2024 (UTC)

The reverse reaction

I'm deleting for the second time this claim:

• The reverse reaction, that is, the decay of a free proton to a neutron, is energetically disallowed, unless additional energy is provided, such as from a high-energy collision of a proton with an electron or neutrino.

I believe the claim is correct but unreferenced. It is correct in the same way as "thing don't fall up" or "it's not dark when the Sun's out". If there is a reference that makes this point we should explain why it is significant. Johnjbarton (talk) 15:14, 1 April 2024 (UTC)

I commented above already under "A sentence on "free" proton decay". You've been harping on "unreferenced", but, as I have already acknowleged above a couple of times, supporting much of this article with proper citations will be an ongoing, lengthy task. I object to suddenly enforcing this standard just now without giving us the opportunity to work through this challenging problem. (Otherwise you'll just delete large sections of the article...to no purpose) Bdushaw (talk) 15:25, 1 April 2024 (UTC)

FWIW I don't delete just because things are unreferenced. I do delete quite a bit of unreferenced material because the content is confusing and without a ref I can't fix it.

I think this paragraph is superfluous. A ref might explain what makes the statement significant and then I could change the content. But it does not have a ref. If one shows up the content can be returned with further explanation. Johnjbarton (talk) 15:52, 1 April 2024 (UTC)

Why half-life?

I removed the free neutron half-life value then @Bdushaw put it back. The references provide the mean lifetime. Calculating then adding the half-life makes the article error prone (see discussion above under topic The "free" neutron - half time'). More important it is confusing for readers. "Why are there two such numbers? Why are they different?" The half-life is extraneous information. If a reader needs half-life it can be up to them to convert. Johnjbarton (talk) 15:19, 1 April 2024 (UTC)

We seem to be working at cross purposes, which I am sorry for. I think it is worthwhile to include both values (mean lifetime and half-life) as a service to the reader; I disagree with the idea of having the reader calculate it for themselves. It is not extraneous to the extent that readers may have encountered neutron "half-life" elsewhere and looked up this article for more information. Recall the reader level is the general public; few will know how to calculate half-life from mean lifetime. I'd be open to just including the value in the table at upper right. Or a brief sentence elucidating the difference. Bdushaw (talk) 15:31, 1 April 2024 (UTC)

Yes, I think we are considering the same kind of reader. But I don't think "both" is service, but a confusion because now they have to ponder two things.

With only the value given in standard refs we are also aligning with standard practice. If a reader only knows half-life from another source, the link to mean lifetime explains the difference. Johnjbarton (talk) 15:48, 1 April 2024 (UTC)