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Contents 1 =Unit of Spin 1.1 Anon comment 1.2 resonances 1.3 Importance in chemistry 1.4 how many neutrons are in helium? 1.5 Half-life of free neutrons 1.6 Category Glitch 1.7 NPOV 1.8 Making a Neutron 1.9 Last Guy Took Out Sievert 1.10 Neutrons, stability, origin, etc. 1.11 Carcinogen? 1.12 Position of diagram 1.13 Radius

[edit] =Unit of Spin

When stating the spin, shouldn't there be a unit (ex. A neutron's spin is 1/2__)

That unit would be h_bar. Though anyone who is familiar with the unit h_bar, knows that a half spin implies 0.5 [h_bar] -guest

[edit] Anon comment

Neutrons and protons both are attached to the nucleus!!

--24.108.178.156 03:50, 6 February 2006 (UTC)

[edit] resonances

I'm not sure the description of particles in a nucleus as resonances between protons and neutrons by exchange of pions is up to date. I remember it was one of the first strong interaction models that appear, but that was before quarks and QCD. Is that description still valid in a quark context?

Yep. QCD provides a little more detail to the picture, of course, but you still get triples of up-downs which correspond to proton-neutrons, and since these are colorless and gluons very sticky you tend to get quark-antiquark pairs connecting them, and these are pions.

I have doubts about whether the statement is correct as written, and even stronger doubts about whether it belongs in this particular place in the article. First of all, I have no idea what the word "typically" is supposed to indicate here. Also, I'm not sure why you'd want to call them "resonances." You could say that they're eigenstates of the three-quark system, which would be incomprehensible to the typical reader. You could use the term "resonances" to indicate that without using words like "eigenstates," but it sounds to me more like a slangy usage, and the general reader is no more likely to understand it. It's true that it's only an approximation to describe protons and neutrons in a nucleus as having permanent, unique identities. In a completely correct, relativistic description of the nucleus based on QCD, the protons and neutrons would only arise as certain correlations among quarks. Well, unfortunately we don't have any such model that's capable of producing useful predictions about nuclei. It strikes me as extremely pedantic to have this statement in here, and it has nothing to do with the stability of the neutron, which is supposed to be the topic of this section of the article.--207.233.84.39 01:25, 28 March 2007 (UTC)

Here is the thing, My name is Jessi and I am in 8th grade we just started learning about Atoms,Protons,Neutrons,Elcrtrons,exc, and i am just haveing some trouble understanding it all. It is so comfusing Aren't we all!! Particularly about subdividing the electrostatic charge on the electron!WFPMWFPM (talk) 03:44, 8 June 2008 (UTC)

[edit] Importance in chemistry

I did a Google search and I got a page saying that neutrons are not important in chemistry. Please complete this sentence:

Although neutrons are not important in chemistry, they are important in... 66.245.84.123 00:53, 28 Sep 2004 (UTC) (No, my IP address is not a part of this sentence.)

Ummm... It's not actually true, although many people who should know better do say that it is. The number of neutrons in its nucleus doesn't make much difference to the chemical behavior of an atom, but it does make some. If you drank enough heavy water to make it replace somewhere between a third and two-thirds of your body water (nobody has tried it), your hair would fall out and any fast-growing cancers would go into remission, owing to the slowing down of some very critical chemical processes in your body. And much chemical research uses radioactive tracers. And depending what you mean by important in chemistry, there's the little detail that the only stable nucleus without any neutrons is hydrogen (or more specifically, protium)! So without neutrons, chemistry would be a little on the boring side, if indeed there were any chemists to do it. Andrewa 01:40, 26 Oct 2004 (UTC)Landorjal danced with her cousin while explainig the meaning of a Neutron.

It is mainly important for hydrogen where the speed of the reaction changes by about a factor of 6 under most circumstances where hydrogen is important. Otherwise, it isn't so important... none the less most living things do show significant preference for certain isotopes Pdbailey 04:09, 23 Nov 2004 (UTC)

Also, neutron are far more important in atomic chemistry (I think thats how you say it). In fusion and fission reactions they play a major part in the process, such as the weak interaction where they release electrons or absord them... well look it up.

[edit] how many neutrons are in helium?

Depends on the isotope. Helium-3 and helium-4 have one and two neutrons respectively and are the only stable isotopes of helium. Helium-6 and helium-8 (4 and 6 neutrons) are beta decayers with half-lives under a second. -- Xerxes 20:35, 2005 Jan 22 (UTC)

[edit] Half-life of free neutrons

I've noticed that there seems to be a very wide range of values given for the half-life of free neutrons. A quick Google search showed up values ranging from around ten minutes to as much as 17 minutes. Even Wikipedea's two entries on the neutron and the free neutron currently give values of 886s and "about ten minutes" respectively.

I have found a reference which gives a measurement with a range of error: http://prola.aps.org/abstract/PRD/v5/i7/p1628_1 The value they give is 10.61 ± 0.16 min (about 636.6 +/- 9.6 seconds).

That source is of 1971, and can be safely ignored. -- Frau Holle 18:51, 11 October 2005 (UTC)

I've not edited any entries to reflect this as I have not found another reference confirming this value and the error range. Perhaps someone will be able to confirm the figures.

I assume that the wide range in published values is a reflection of how tricky it is to make the measurement. It would be interesting to hear if this is the case.

Indeed these conflicting half-lives can certainly lead one into dubious waters. This simply comes down to the instrumentation used by laboratories independent to each other. One lab might use a gas chamber detector while another might use a scintillation detector with less dead time. I understand the consensus among many nuclear and particle physicists is that the half-life lies somewhere between 10.2 and 10.6 minutes. — oo64eva (AJ) ^{(U | T | C)} @ 14:53, Apr 15, 2005 (UTC)

State of the art as of 2003: 886 +- 2 s [1]. -- Frau Holle 18:51, 11 October 2005 (UTC)

Please note that using the term half-life is not applicable in case of free neutrons. Scientist woulde be very happy if it would have been half-life, since they could have taken ultra cold neutrons home in a so called neutron bottles (to cook some neutron cakes:). The term half-life involves something fusing by half during half-life period. In that case neutrons would have fused with different times what is actually not happening since every single neutron will fuse in 886 sec (or about that time). And I'm actually not sure if the term mean lifetime is aplicable in that case as well since I'm not a specialist in particle physics. I'm doing some neutron spectroscopy. -- 195.83.126.10

Huh? Sorry Mr. Unsigned IP Address, that's crap. Neutrons do have a well defined half-life. They do not all decay at the same time, but probabilistically like all other particles. Moreover, decaying is not "fusing". "Fuse" means "combine". --Strait 17:55, 28 August 2006 (UTC)

I recommend that we use the Particle Data Group's figure for the lifetime. http://pdg.lbl.gov , in particular http://pdg.lbl.gov/2006/tables/bxxx.pdf , page 4) It is updated regularly and is a trusted name in physics. --Strait 17:55, 28 August 2006 (UTC)

It's important not to confuse "Half Life" with "Lifetime". Half life is defined as the time after which the particle has a 50% chance of decaying. Mean lifetime is longer than half life by a factor of 1.44 (see the article Mean_lifetime) since the average includes particles that live for much longer than the half life. I'm sure this is causing the apparent discrepancy. So for the neutron, mean lifetime is 886 seconds, but the half life is only 886 * ln(2) = 614 seconds. Lokster 13:26, 4 June 2007 (UTC)

Added the free neutron mean lifetime from the PDG (mine is 2006) (on the net at: http://pdg.lbl.gov) As a particle physics grad student, I strongly recommend using PDG values whenever possible, as it is a common standard. naturalnumber (talk) 10:47, 23 April 2008 (UTC)

[edit] Category Glitch

What's up with the categories appearing on the top of the page? ‡ Jarlaxle 21:42, July 25, 2005 (UTC)

News! teleronci:Newly calculated elementary particle of a rest mass = 1.15819171.10^-30 kg which is included as an integer value in the rest mass of proton and neutron (Source: Meissner, R.: das Teleronki-Modell..., Aachen: Shaker-Verlag 2001.)

[edit] NPOV

I've removed the NPOV from the article and placed it here - since the anonymous inserter didn't see fit to discuss it first. Are there any grounds for believing the article is NPOV?? Thanks, Ian Cairns 13:13, 30 September 2005 (UTC)

Looks like an unusual form of vandalism to me. Tho I haven't been very pleased with some recent edits to this article, I wouldn't call them POV. -- Xerxes 15:57, 30 September 2005 (UTC)

I removed the tag altogether so it won't show up in the NPOV disputes category. -- Kjkolb 08:16, 9 October 2005 (UTC)

[edit] Making a Neutron

Does anyone know if there are any theories to the possibility that the Down Quark is composed of an Up Quark and an electron? I once heard that when a Proton and Electron mix it produces a neutron. So if this is true then if you mix an Up Quark and an electron it must form a down quark...I am not sure though. - BlackWidower

To answer your question, quarks are supposed to be fundamental particles - nothing inside. A down quark can decay into an up quark; this transition creates a W- boson, which quickly decays into an electron and anti-neutrino (and these are detected). This does NOT mean the electron is inside the quark to begin with! Check out the wikipedia article W_and_Z_bosons. Hope this helps. Lokster 13:33, 4 June 2007 (UTC)

[edit] Last Guy Took Out Sievert

Neutron radiation is especially damaging to organisms due to it's penetrating qualities, and ability to damage DNA. The Sievert weights radiation exposure by it's damage to human physiology. A person may feel that exposure to 5 rads of Neutron radiation isn't a big deal (5 rads of photons is not that horrible), but it is, and the Sievert radiation scale shows this clearly. Please don't take it out again. --Wiki Tiki God 09:59, 2 November 2005 (UTC)

No offense intended by its removal. I understand what a Sievert is, and it's not directly pertinent to neutrons. If people want to read about neutron radiation, they'll click on the neutron radiation link. Seeing as how the See Also section for this article is extremely long already, I think we need to adopt a strong standard of relatedness for additions. But, of course, I'll defer if others disagree. -- Xerxes 16:21, 2 November 2005 (UTC)

Actually, tho I still think everything I say above is true, I think Sieverts looks good where it is, so I'm not recommending we should take it out. -- Xerxes 16:24, 2 November 2005 (UTC)

[edit] Neutrons, stability, origin, etc.

What part do neutrons play in maintaining the stability of the nucleus? How do neutrons ever find their protonic mates in the first place, ie. especially when making new atoms? (That reminds me, when making artificial matter like I don't know, element 114, is it mandatory to find some neutrons to collide with the protons in order to produce an atom?) -- Natalinasmpf 12:13, 5 November 2005 (UTC)

Neutrons enhance the stability of a nucleus by increasing the amount of strong nuclear force felt by the nucleons. Both protons and neutrons generate the roughly the same amount of attractive strong force. However, neutrons are not charged, so they do not generate repulsive electric force like the protons do. Thus, a nucleus with neutrons is more stable than one made entirely of protons. In fact, there are no stable nuclei without neutrons except a single proton.

Neutrons find their protonic mates during fusion reactions. These typically take place deep in the hearts of stars like the sun. Fusion may also take place in the shockwaves of supernova explosions at the end of a large star's life. Some elements, like helium and some lithium were fused during the first few minutes after the Big Bang, when the entire Universe was hot enough to sustain fusion.

When scientists build heavy nucelei out of smaller nuclei, they try to start with two smaller nuclei that have as many neutrons as possible. That way, the resulting larger nucleus will have enough neutrons to be more stable. It's important to note that they don't put together huge nuclei from individual protons and neutrons, but just from two smaller large nuclei. -- Xerxes 17:57, 5 November 2005 (UTC)

Wouldn't neutrons start to be counter-productive though, if regarding stability for large atomic masses, since adding more mass as an already heavy atom (ie. bigger than uranium) gets larger would contribute to instability? You completely answered my previous question though, it just evokes my curiosity further. Why do large atoms become unstable in the first place: do the forces pulling them apart overcome the strong nuclear force at larger masses? -- Natalinasmpf 23:17, 5 November 2005 (UTC)

There's a tradeoff involved. Although neutrons increase the amount of strong binding energy, they are heavier than protons and subject to beta decay. Once your nucleus gets too many neutrons in it, some of the neutrons will beta decay into protons. For very large nuclei, the whole nucleus just becomes so big that you get spontaneous fission. It splits roughly in half.

You can look at a chart of how various nuclei decay at NuDat2 -- Xerxes 00:51, 6 November 2005 (UTC)

[edit] Carcinogen?

Anyone know why "neutrons" are listed under List of IARC Group 1 carcinogens. Umm, what? —The preceding unsigned comment was added by 130.71.96.23 (talk • contribs) .

Clarified that to "neutron radiation". Femto 13:55, 29 May 2006 (UTC)

[edit] Position of diagram

The diagram is just schematic; it is not a "picture" of a neutron. It deserves no more prominence than the quark-model content, which is where I think it belongs: in the table with the quark content. -- Xerxes 20:41, 8 June 2006 (UTC)

[edit] Radius

Is neutron really 10x smaller than proton?

Here neutron: Radius variable, about 1x10^-16. At proton page: Diameter: about 1.5x10^-15.

Either of these values is bad, or it will be usefull to note such discrepancy...

No, they are about the same size. This is true because the strong force, which is most of what holds them together, doesn't distingish significantly between up and down quarks. Let's try to untangle what's going on here...

I have the Review of Particle Physics 2006 in front of me. It says that the proton "charge radius" is 0.875±0.0068 fm. While the RPP does not define charge radius, Perkins' "Introduction to High Energy Physics" says that it is the root mean square of the charge distribution. Now, this is only a precise way of characterizing the size of the proton if what you are interested in is its electromagnetic interactions, since one could easily imagine that the RMS of its color charge distribution could be somewhat different. In any case, twice this radius gives 1.75 fm, which, I guess, is "about 1.5 fm".

The RPP gives the neutrino "mean-square charge radius" as -0.1161±0.0022 fm². What this means ([2]) is that the core of the neutron is somewhat positive and the outside is somewhat negative. Clearly, this isn't a good measure of its size at all, because if you calculate the RMS, it's not real. If one charges boldly ahead and ignores the minus sign, one gets 0.341fm, so I don't think that's where the 0.1fm the article currently has came from.

I'm having trouble finding a source that will parameterize the size of the neutron in any other way while also giving a precise value. Povh et al's "Particles and Nuclei" says that "nucleons have radii of about 0.8 fm." Let's use this value until we can find something better. --Strait 23:52, 6 September 2006 (UTC)

In the liquid drop model, there is a parameter that can be interpreted as the radius (or volume, or whatever) of a neutron or proton. There are various versions of the liquid drop model, and in some of the fancier ones, with tons of free parameters fitted to all the known binding energies and so on, it's possible that they parametrize it separately for the neutron and proton. In any case, nuclear matter is somewhat compressible, so it's not really valid to think of neutrons and protons as having fixed, specific sizes regardless of the nuclear environment they find themselves in. The electromagnetic moments have the advantage that, they have precise definitions, and, at least in theory, could be measured to arbitrary precision for the free particles. However, that really tells you next to nothing about the physical size of the particle. The thing that comes closest to being interpretable as a size of the nucleon is the liquid drop parameter. The electromagnetic moments are important more as tests of QCD. The radius appearing in the liquid drop model is more like 1.1 fm, so that's really what should be in the article -- or maybe just 1 fm, since to define it with two sig figs of precision, you really have to be careful in explaining what you mean. (In de Shalit and Feshbach, a best-fit value of 1.12 fm is given, but you don't want to take the extra sig figs too seriously -- it depends entirely on what kind of data you're fitting.)--207.233.84.39 01:41, 28 March 2007 (UTC)