Talk:Nuclear magnetic resonance

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Contents

[edit] Diagram needs changing

The diagram that demonstates the splitting of the electon spin energies is wrong with the lowest energy being negative. This is not the case, in NMR the lowest energy of the split angular momentum is positive in value. Would be great to see this changed if any one still has the original .jpeg. EPR is the spectroscopy that has a negative value for the lowest split energy value125.238.142.222 (talk) 10:02, 28 May 2008 (UTC)

[edit] whoo ... big edit.

I divided the page sections, and greatly expanded the description of how NMR works. This is the closest I have ever come to giving a quantum mechanics lecture! Please help with any parts that are unclear...

The history section needs better organization, although I'm grateful for whoever put that up there. More discussion of various techniques (FID, spin-echo, CPMG) is necessary, as is discussion of the various factors that are measured by NMR spectroscopy. --hb, 18 Nov 2002

[edit] Discovery of chemical shift

In the history section, it would be nice to add a couple of sentences on the discovery of chemical shift and how Bloch commented that if this were "some nasty chemical phenomenon" it could "terribly impede" the measurment of nuclear magnetic moments. Detials of the story can be found at http://www.ebyte.it/library/hist/ProctorWG_Reminiscences.html Roy Hoffman 11:20, 26 March 2006 (UTC)

[edit] sections need to be removed.

The description of the NMR signal as reading the radiation that comes out when the nuclei reequilibrate needs to be removed. This is a common misconception about what the NMR signal is. Both T2 and T2* measurements are made while the nuclei are in disequilibrium; although the bulk magnetization decreases, it is because the signals are going out of phase with each other (because they are resonating at different frequencies), not because the nuclei are reequilibrating. (anonymous, 18 Feb 2004)

To me, the text seems to be correct, although it might lead to some confusion that T2 (dephasing) is discussed directly after the re-equilibration, which would refer to T1 (population relaxation). I tried to clarify the text (then saw that I mixed up T2 and T2*) - Hankwang 21:53, 18 Feb 2004 (UTC)
I would rewrite the section completely in terms of commonly used names for T1 and T2 - (it can be either longitudinal and transversal or spin-lattice and spin-spin relaxation). It's odd to mix up T1 and T2 together because generally the processes of spin-lattice and spin-spin relaxation are independent both in classical terms (Bloch equations) or in QM therms (Redfield theory, etc). Moreover, the difference between T1 and T2 may be several orders of magnitude ( when speaking about solid-state NMR). Generally, the T2 can not be dependent on T1, especially in such a strange manner like placed in the formula in the bottom of this section. What is the source of such an odd relation between T1 and T2 ?? MakVal
In order for the spins to relax fully, they must also stop precessing in unison. That is the link between the two. --Pdbailey 00:08, 10 May 2005 (UTC)

[edit] Magnetic or electromagnetic?

Concerning the sentence: "When radio power is sent to the antenna, it generates an oscillating magnetic field H1 (not to be confused with the external magnetic field). "

should this not be "..generates an oscillating electromagnetic field"? Foppe Brolsma, brolsma_produkties (at) hotmail.com

No, the current text is correct. To call it an oscillating electromagnetic field would imply it were electromagnetic radiation, which it isn't. -- Tim Starling 00:45, Mar 19, 2004 (UTC)
The fact that it is a radio antenna which generates the field implies that it is electromagnetic radiation. Moreover, the text mentions left-handed and right-handed circularly-polarized photons, which also implies it is radiation. What you might mean is that
1. we are dealing with the near field (i.e. less than a wavelength from the radiation source), which means that E and B are not necessarily perpendicular. However, NMR would work just as well in the far field (e.g. at higher radio frequencies that have a shorter wavelength) so that is not the issue here.
2. It is the magnetic component that interacts with the nuclei. However, in the description of quantum-mechanical transitions in atoms in an electromagnetic field, it is mainly the electrical component that acts on the atoms, but that is not a reason to call it "transitions involving an oscillating electric field" instead of "radiative transitions".
Yeah OK, that could be right, sorry. When I was taught this initially, we used the semi-classical treatment which talks entirely in terms of a rotating or oscillating magnetic field. Chapter 3 of this random web site, which I found using this google search, uses terminology very similar to what I'm used to:
A coil of wire placed around the X axis will provide a magnetic field along the X axis when a direct current is passed through the coil. An alternating current will produce a magnetic field which alternates in direction.
In a frame of reference rotating about the Z axis at a frequency equal to that of the alternating current, the magnetic field along the X' axis will be constant, just as in the direct current case in the laboratory frame.
This is the same as moving the coil about the rotating frame coordinate system at the Larmor Frequency. In magnetic resonance, the magnetic field created by the coil passing an alternating current at the Larmor frequency is called the B1 magnetic field. When the alternating current through the coil is turned on and off, it creates a pulsed B1 magnetic field along the X' axis.
I'm happy to go with common usage, whatever that may be. Do you have any references calling it an electromagnetic field? -- Tim Starling 15:08, Mar 19, 2004 (UTC)
Well, no, I was merely countering the statement that "it is NOT E-M radiation". :) I'd say the current article text is fine. I certainly would not agree with the moving-coil description above since a correct transformation to a rotating coordinate system would be much more involved than is suggested. The rotating-wave approximation which lies behind this is purely quantum-mechanical, and after this approximation, it turns out that you can describe the precession of the spins in a rotating frame as if there were no B0 field. However, I strongly oppose to "deriving" the approximation from a macroscopic and incorrect metaphor. -- Hankwang 16:52, 19 Mar 2004 (UTC)

[edit] Nuclear spins do not emit radio waves

Nuclear spins do not emit radio waves in response to a radio frequency pulse. This mistake has been repeated in so many text books that no doubt many people believe it. David Hoult, an impeccable physicist, made a valiant attempt to correct this misconception in 1989. The reference is: D. L. Hoult, Concepts in Magnetic Resonance, 1989, 1, 1-5. The wise reader will start here. -Jan Wooten

Wikipedia:Be bold in editing pages -- Tim Starling 06:25, May 16, 2004 (UTC)
Agreed. What was there was a poor O-chem understanding of the process. I fixed it up a little but left it looking like a first draft... come on wiki process! Pdbailey 05:23, 13 Nov 2004 (UTC)

Hm...Nuclear spins do not emit radio waves...so what about radiation damping (a serious problem in NMR spectroscopy on water containing samples)....rather the NMR signal is an interaction between the ensemble of nuclear spins (coherence) and the RF coil which detects the signal..according to energy conservation (1. law of thermodynamics etc.) there must be some kind of emition, this is trivial. It seems to me that people confuse the quantum mechanical and the clasical description of NMR. I agree that NMR is not directley comparable to spectroscopical techniques like fluorescence spectroscopy or similar (because off the large difference in energy), but formally it is correct that the nuclei emit a signal...although only a very smal portion of this signal is measurable. The NMR signal is a macroscopic quantity...but only due to technical reasons.Flogiston 22:44, 6 October 2006 (UTC)

[edit] Cosy section

The COSY section should be removed/sidelined until it can be explained better. It reads scattily, as if pulled directly from a textbook, and there are many technical aspects unexplained (double Fourier-transformation, Pulses, how the 2nd dimension arises) and many aspects are poorly written (Example of ethanone). I feel this doesn't make it an asset to this entry.

Any feeling/input on this would be appreciated because its a very major edit! Unless anyone objects I'll be removing it when I edit the theory of this section. (And hopefully have time to put something meaningful in its place). Let me know --Lee-Jon

The COSY section deals with other aspects of 2D NMR as well and should be part of a separate entry entitled 2D NMR or Two dimensional NMR Roy Hoffman 13:20, 27 December 2005 (UTC)

[edit] How NMR Works - major edit

The How NMR Works section has been renamed to Theory... and consigned to the latter part of the article so not to frighten undergraduates etc. It has been expanded so (hopefully) every concept makes sense and has some theoretical background presented.

Sections I (or you!) want to add are on spin-spin coupling, Pulse NMR & Fourier-transformation, and possibly a brief talk on the nuclear Overhauser effect relevant to NMR. I think that covers almost everything to give some detail on NMR without it being too technical. --Lee-Jon 21:52, 9 Mar 2005 (UTC)

  1. Nice addition! Thanks. Good work in my opinion. I took out the line between the Image tag and the first line of text--to accommodate "some" browsers.
  2. We might experiment with controlling the size of the Progesterone plot, see code in edit view to produce the diagram to the right. [NB: IMAGE REMOVED] ---Rednblu | Talk 22:15, 9 Mar 2005 (UTC)

Thanks for praise. Yeah I agree with the image - it looks much nicer that way -i've amended it and taken the code out of the edit page. Although I feel the COSY section need much refinement, maybe even a major edit to make it a "2D NMR/Experimentation" section. Lee-Jon 21:12, 10 Mar 2005 (UTC)


A layman here trying to understand the theory and I am bother by the use of quantum numbers in the article. In one place, the spin quantum number is call 'ms' (I can't do the formating correctly) and then later it is called 'I'. I realize that one is 'overall' and the other is not but to a layman I cannot tell if that is a real difference (ie a technical term) or if it is something else, especially when other linked articles on quantum dynamics call 'I' something else again. Here is the quote of the beginning and end of the section: "rise to the spin quantum number, ms........... ½ to the nuclear spin quantum number, I." Since I do not know what I am talking about, anyone who edits this, once fixed, please remove my comment. Cheers!

Sorry, layman again. In the following section: "The spin angular momentum of a nucleus can take ranges from +I to –I in integral steps. This value is known as the magnetic quantum number, m. For any given nucleus, there is a total (2I+1) angular momentum states. Spin angular momentum is a vector quantity. The z component of which, denoted Iz, is quantised: Iz = mh/2π where h is Planck's constant." Iz = mh/2Pi but m can be a range of values (from +I to -I, yes?) so how can i determine Iz? Please erase this after correction.

[edit] Splitting the NMR page in two- NMR and NMR spectroscopy

I am an organic chemist and I would describe myself as an experienced user of NMR spectroscopy. I can not claim to be an NMR expert, I could never write my own pulse sequences etc. I also teach introductory organic chemistry, covering the basics of 1D proton and C-13 NMR in the first semester, then students get to run a COSY and a DEPT experiment in their second semester. I am therefore very familiar with explaining the basics of the NMR spectroscopy. It seems clear to me that there are two different topics covered on this page currently

  1. Nuclear magnetic resonance- the physical phenomenon, and
  2. NMR spectroscopy- the analytical technique.

For example MRI (as I understand it) uses the phenomenon of NMR, but is clearly distinct as a technique from NMR spectroscopy.

This difference between physical phenomenon and analytical method has already resulted in there being separate pages for Infrared and Infrared spectroscopy, also Ultraviolet and UV/VIS spectroscopy. See Category:Spectroscopy for other page titles.

NMR spectroscopy is the most widely-used technique in modern organic chemistry and it surely deserves its own page. The spectroscopy page should have less discussion on the theory and physics, and much more on how the technique can be used to analyse molecular structure- things like equivalence, chemical shift, integration, multiplicity, diastereotopic protons in chiral molecules, which nuclei lend themselves well to analysis and which don't, etc. Some of this information is already on this page, much is not. My undergraduate students would currently find almost nothing on this page of value to them. We need this separate NMR spectroscopy page. The COSY section could be part of this new page or could be big enough for its own page. What do others think? Walkerma 07:14, 14 May 2005 (UTC)

PS: I should mention that I have an ulterior motive- we are currently revamping the standard data table for chemical compounds, and we are including a link (for some compounds) chemical shift data or to scans of actual 1H and 13C spectra. The idea is that when you look up (say) limonene, you could click on a link to see NMR data or a spectrum. I would like to have the standard "explanation" link on these tables to lead to a spectroscopy page. Walkerma 07:21, 14 May 2005 (UTC)

[edit] Good idea

I agree, however NMR Spectroscopy extends far beyond Organic chemistry so maybe the page could be written from a few angles:

  1. Sample preparation
  2. organic structure (typical stuff)
  3. biological structure (structure/function etc)
  4. dynamic NMR (reactions/thermo etc)
  5. Solid state NMR
  6. multinuclear NMR (13C 15N 17O etc)
  7. Techniques (multidimensional etc)
  8. Fourier transformation and computational methods

Unlike UV/VIS and similar techniques, modern NMR Spectroscopy is a very large and very complex area. And as I'm sure you're aware, an end-user approach to NMR is very difficult to discuss without having to delve into some nuclear physics. Any section on NMR Spectroscopy should continually reference a theory section to keep it accurate.

The page has been created here and I'll try and finish a good first build throughout this month! Lee-Jon 09:11, 17 May 2005 (UTC)

Thanks for starting that- it's a nice job so far! Please can I encourage you to keep writing it at a very basic level. I know from teaching this, you only need a very basic understanding of the physics underlying it- just like you don't need to understand general relativity to understand that an apple falls to the ground. I would avoid getting into discussions of T1, T2 etc. on this page if possible. Also, can I recommend that this page be renamed as NMR spectroscopy (small s) (currently a redirect), this seems to be the more usual form when you look at [[Category:Spectroscopy. I agree that all of those topics need covering- these probably all warrant their own pages. Wikipedia is exploding in size and depth, it seems to me, and with the chemical compounds pages we probably have 500-1000 compounds covered, up from perhaps 100-200 a year ago- so having 10 pages on different aspects of NMR, written at various levels, is totally reasonable. I would suggest that 13C deserves its own page. One small point, should that be "heteronuclear" NMR for 15N etc? Multi to me implies many, which sounds like HETCOR, APT etc. Walkerma 16:53, 17 May 2005 (UTC)

Thanks for the comments. You're right, when I said multi I meant hetero. Typing faster than I'm thinking! Agreed about the small "s". I'll change that. Lee-Jon 09:08, 19 May 2005 (UTC)

[edit] Splitting up & Solid-state NMR

I am a bit torn apart in my feelings for splitting up the article on NMR and it's spectroscopic technique. From a scientist's point of view, I oppose this. However, for an Encyclopedia, it's important to be not only accurate and precise, but also brief. Therefore it might be good to proceed to disentangle the "physical phenomenon" and the "spectroscopy", setting the appropriate links. Aside of that, I suggest to write a separate article on solid-state NMR, which may be broken up into two sections describing the effect and the spectroscopy if you show this can be done successfully.

[edit] Fullerene NMR

In their 1985 experiment, R. Curl and R. Smalley of Rice University obtained mass spectrum of carbon clusters, where even numbers have large intensities and n=60 is particlularly so (Nature, 1985, 318, 162). They proposed the C60 structure as a soccer ball.

The NMR spectrum of buckminsterfullerene (C60) was published in 1990 by another Nobel prize winner Kroto, H.W. of University of Sussex (J. Chem. Soc., Chem. Commun. 1990, 1423). This confirmed the earlier proposed structure. Indeed, IR spectrum of C60 precedes NMR (Nature 1990, 347, 354). Together, IR and NMR spectra confirmed the structure of C60.

This entry need to be changed to reflect this fact.

[edit] needed

I think the article could use a nice diagram of the innards of an NMR machine and an explanation of how the larmor frequency relates to the naming of individual machines (field strength correlation etc.) though, I am not the one to do it. I can't find a good PD diagram of an NMR device so.....any takers?--Deglr6328 20:11, 18 Jun 2005 (UTC)

[edit] NMR in weak fields & outside of RF coils

Is someone familiar with NMR and NMR spectroscopy in weak magnetic fields and outside of the RF coil, as for oil logging or material science (like the NMR mouse tool that the guys from RWTH Aachen build)? I've heard a couple of interesting talks about it, but I don't feel qualified writing about it. However, I think those are some nice applications in engineering that would extend the "molecular structure" view of the current NMR articles a bit, and may be of interest to readers outside of the field. Would be cool if someone picked that up!


NQR?--Deglr6328 12:48, 30 August 2005 (UTC)
I was talking to a retired fellow today who did NMR for oil prospecting, and he said that they could do meaningful detection of sunken ships/submarines, through NMR from the air. This is one of his adventures: http://www.users.bigpond.net.au/Sydney_search/KDLS_Search_Report.html
A brief description of the equipment: http://www.users.bigpond.net.au/Sydney_search/kdls.html
I'd like to know more too. RB30DE 09:29, 18 October 2006 (UTC)
The effect you refer to is evidently "Earth's Field NMR" (EFNMR), (as distinct from NQR). I have added two questions relating to EFNMR below. GilesW 01:14, 14 April 2007 (UTC)

[edit] kindly stop using acronyms

Especially when naming the subpages. I will proceed to rename them in order to conform to the Manual of Style (as well as professionalism)...well, that's my rant of the day, off to formalise dozens of other articles...keep a look out for double redirects. There's something gratifying about the term "magnetic resonance", I don't see why we have to abbreviate it to such a horrible acronym. ;-) Elle vécut heureuse à jamais (Be eudaimonic!) 00:08, 17 February 2006 (UTC)

Acronyms are in common usage in the field of NMR (and in science in general). Often people don't actually know what the acronyms stand for. And in addition to this it get's a bit laborious to say eg. "insensitive nuclei enhanced by polarization transfer" rather than just INEPT. The acronyms that are in common usage should stay.... Kjaergaard 08:05, 17 February 2006 (UTC)
Yes, but you don't use them for article titles. Using them in the article body text is tolerable, (and should generally not be wantonly done). Look at some of the pages - it reads like heiroglyphs. There is no excuse for this: how do you expect a new reader to understand? Look at protein nuclear magnetic resonance, a version which I will correct:

...The HNCACO only contains the one from the previous residue, and it is thus possible to assign the carbonyl carbon shifts that corresponds to each HSQC peak and the one previous to that one. Thus it is possible to make the assignment by matching the shifts of each spin system's own and previous carbons. The HNCA and HNCOCA works similarly, just with the alpha carbons rather than the carbonyls, and the HNCACB and the CBCACONH contains...

It is utterly ridiculous: These acronyms are ambiguous, and may be professional in a scientific journal, but not for an integrated encyclopedia. Besides, it shouldn't be laborious; Wikipedia isn't paper. We can spare the use of long titles, just as long as it isn't unwieldy. Generally we can tolerate titles of 6-7 words, even, although more than that will be a good excuse to use an acronym. It's precisely that people don't know what the acronyms stand for that it is a concern. After all, very little do acronyms end up like video and radar, generalisation of these acronyms are the exception, not the norm. Sorry for the rant here, I'm just a copyeditor who has to make sure the text is legible - also "see this article for more details" should not be done. It's a horrible and unprofessional way and disrupts prose. The guideline is to remember that we also have a "spoken Wikipedia" project, and so if you can't imagine reading an article say, to a class, and saying some of the phrases (such as "see this"), then it generally should not be included. This excludes "main article" (which should only be done for sections) or special notices. Elle vécut heureuse à jamais (Be eudaimonic!) 20:38, 17 February 2006 (UTC)
1st let me just say LOL, just to waste further the whole point here. This article alone has wasted the usage of the acronymic term more than plenty. Science is deterministic on change and opposing forces that challenge. Acronyms are many and are a nuance to the community as a whole. Change in this sense will assist those who 'want' to learn more than just 1n variation of the term mr. (Even when the subject field is as evident as it can be) anon 203.59.189.244 19:42, 15 June 2007 (UTC)
Take the time for us, or to tip a cow, TTTFU || T3FU anon 203.59.189.244 19:57, 15 June 2007 (UTC)

I've tagged protein nuclear magnetic resonance for cleanup. Can someone convert the acronyms into actual concepts, formalise the page, then remove the tag when done? So basically, acronyms are tolerable, just don't use them in page titles, or use them wantonly. HNCA and HNCOCA need to be converted, too. Elle vécut heureuse à jamais (Be eudaimonic!) 20:52, 17 February 2006 (UTC)

Ahhh... Again one of those cases where people want to edit something they don't know anything about. HNCA and HNCOCA are just names, so they cannot be converted. I do not agree, but I don't feel strongly about it, . If you want to rename the Protein NMR page, call it protein nuclear magnetic resonance spectroscopy instead. Kjaergaard 21:47, 17 February 2006 (UTC)
I know about spectroscopy in general, but that's not the point. I just want to make sure that I can convert the article from heiroglyphs to prose (even if it's abstract prose), so I can nominate it for Wikipedia:Featured article. Please don't revert me - I made a lot of legitimate changes - I am simply bringing the article in line with the Wikipedia:Manual of Style and copyediting the page. Elle vécut heureuse à jamais (Be eudaimonic!) 05:19, 18 February 2006 (UTC)

[edit] Failed Good Article candidate

The main reason for my failing this is the fact that the article tends to blur the difference between NMR the physical phenomenon (the subject of this article) and NMR spectroscopy (the application of said phenomenon, covered mainly in the NMR spectroscopy article). This is understandable because (a) both topics used to be covered on this page and (b) chemists tend to talk about "an NMR" when they mean an NMR spectrum. The applications of NMR in spectroscopy and MRI are important and deserve coverage, but they should not be in place of NMR as a phenomenon. The History section (after the first four paragraphs) reads more like a history of NMR spectroscopy rather than of the study of the phenomenon itself (ironically, the spectroscopy page doesn't include any of this same history!). This is a bit like reading the article on microwaves and finding the history of the development of microwave ovens described, simply because "microwave" in the vernacular refers to the ovens. To someone unfamiliar with the topic, this must be very confusing.

The theory section seems fine - sure, it's technical, but then again this is a pretty technical subject. Terms are explained as they should be.

The "Uses" section really needs a single person to rewrite it into a coherent section. It reads like 50 different people have thrown in bits of information - the content is there, but it needs organising and rewriting in places (e.g. the C60 paragraph). I would like to see subsections of Uses

  • Magnetic Resonance Imaging starting with {{Main|Magnetic Resonance Imaging}} then an overview of MRI.
  • NMR Spectroscopy starting with {{Main|NMR Spectroscopy}} then describing the main uses of NMR spectroscopy.
  • Other uses as described.

I also suspect there may be some things missing from here, and moving inappropriate spectroscopy stuff elsewhere would create the space for this. I'd like to see listed some of the elements that are most active in NMR. The Nuclear spin and magnets section explains which will be active, but some examples like why 12C is inactive but 13C is active. I'd like to see discussion (in simple terms, perhaps purely qualitative) of the sensitivity of the nucleus - why 1H is easy to see, but 15N is not. Could it include how quadrupolar relaxation can smear out a signal and make it harder to observe with a nucleus like 51V? I'm not knowledgable enough to write this material, but I suspect this article could have a lot more useful content. Walkerma 03:27, 17 June 2006 (UTC)

[edit] T2

There is no explanation or Wikilink of what T2 is. It's just dropped in. --Scottandrewhutchins 22:16, 19 January 2007 (UTC)

It's explained on the MRI page, but it needs to be explained here. --Scottandrewhutchins 19:36, 24 January 2007 (UTC)


Additionally, T2* needs a better description. It is used without explanation --Evan and Gabe, MIT students doing an NMR experiment

[edit] Noise-to-Signal Ratio

The problem of poor noise-to-signal ratio is mentioned under the CONTINUOUS WAVE SPECTROSCOPY section, and the subsequent need therefore for signal averaging.

As I understand it however, poor noise-to-signal ratio is a problem inherent to the NMR process itself, not just CW Spectroscopy but also FOURIER SPECTROSCOPY. No signal-to-noise aspects are discussed under the FOURIER SPECTROSCOPY section of the article however.

Perhaps the issue of signal-to-noise needs it's own heading and section, separate from CONTINUOUS WAVE SPECTROSCOPY to make things a little more clear.

Pookie69 11:51, 2 April 2007 (UTC)

[edit] Earth's Field NMR - EFNMR

I cannot find a reference to EFNMR in wikipedia, though there are good web pages about it. I suggest adding a reference to it, and developing an article. GilesW 12:00, 13 April 2007 (UTC)

Links to (updated) Magnetometer article and an EFNMR web site added to article. Stub page for EFNMR needed. Editor, please help. GilesW 09:09, 20 May 2007 (UTC)
I have drafted an EFNMR page, some time ago now, help welcome, GilesW 13:06, 20 September 2007 (UTC)

[edit] Proton Precession Magnetometers etc

I suggest adding a link from the NMR article to the Magnetometer article, which discusses PPM and Overhauser magnetometers. I notice that the Magnetometer article does not mention that these are EFNMR effects. Perhaps this should be remedied, once the EFNMR references are in place. GilesW 12:08, 13 April 2007 (UTC)

Done, GilesW 14:04, 30 May 2007 (UTC)

[edit] Quantum computing

Why is this not even mentioned? And the article is too big btw. Hard to find necessary things

[edit] Gah an edit!

article reads:"NMR studies magnetic nuclei by aligning them..." Should it not read:"NMR studies magnetized nuclei by aligning them...". Correct or elaborate please, in a strong enough magnetic field all nuclei can be influenced, essentially the flow of energy is directly influenced to produce statistically strong/weak results, albeit lamonistic. anon 203.59.189.244 19:15, 15 June 2007 (UTC)

  • Well, like much else in this curate's egg of an article, the basic premise is wrong. The interaction between the nuclear spins and external magnetic fields is far too weak in comparison with thermal energy to cause "alignment" of the nuclear spins - you'd have to be extremely close to absolute zero for significant alignment. Unfortunately explaining this properly is not easy - the Keeler reference does this well. 84.92.241.186 11:19, 16 June 2007 (UTC)

[edit] Help needed with ZNMR and EFNMR

Help with Zero Field NMR, Earth's field NMR, and Electric field NMR articles needed, please.

Plus a mention in the text of the main article. Earth's field NMR is a poor relation, but significant (bore hole logging, magnetometers etc).

Any thoughts about sorting the 'See Also' list into alphabetical order? GilesW 16:29, 16 June 2007 (UTC)

Done GilesW 10:44, 22 September 2007 (UTC)

[edit] Edits to Introduction

The wording of the introduction is orientated towards NMR spectroscopy in high-field laborotory environments, and is not applicable to some other applications of NMR. Furthermore it is rather abstract. I propose that the intro be generalised to make it applicable to Earth's field NMR etc.

See above for various references and questions re EFNMR etc.

The following quote is helpful and could be used with attribution or paraphrased:

"... the [stimulating] frequency necessary to cause nuclear transitions is different for each element or isotope. The resonance frequency is found to vary in direct proportion to the applied field (for all magnetic nuclei); thus the larger the magnetic field the larger the frequency necessary to achieve resonance." [[Kemp, W. NMR in Chemistry : a multinuclear introduction Macmillan Ist Ed 1986 p6.]]

In addition, may I suggest something like:

In the laborotory, NMR studies magnetic nuclei by aligning them with a very powerful external magnetic field and perturbing this alignment using a high frequency magnetic field. The resulting high frequency magnetic field generated by the sample in response to the external perturbing magnetic field is the phenomenon that is exploited in NMR spectroscopy and magnetic resonance imaging.

In the Earth's magnetic field, NMR frequencies are in the audio frequency range, and are typically stimulated by applying a strong dc magnetic field pulse to the sample and analysing the resulting low frequency alternating magnetic field. This effect is exploited in some types of magnetometer and on-location EFNMR spectroscopy.


NOTE: The perturbing fields are generated by inductors, so have no electric component. Electromagnets do not generate electromagnetic fields!

GilesW 21:45, 23 June 2007 (UTC)

Edits now incorporated broadly iaw the above. GilesW 11:28, 24 September 2007 (UTC)

[edit] Bloch Equations

Something is missing in this article: Bloch equations. TomyDuby 22:52, 3 July 2007 (UTC)

[edit] CW versus Pulsed NMR

I am missing a discussion on these two modes. TomyDuby 23:00, 3 July 2007 (UTC)

This page indicates that NMR uses pulsed magnetic fields What's up with that?
One college that I visited used a pulsed magnetic field NMR unit as well--what's up with that?
A university professor physics PhD that I had as a work colleague described NMR in terms of an impulsed magnetic field--what's up with that?
This NMR article also talks about impulsed magnetic fields!--What's up with that?
I, too, want to see this CW vs Pulsed NMR differentiation addressed.
The article on Earth's field NMR (see also) seems to have 'fewer proponents' and is flagged with a number of wiki templates of critisism. Experts, please help out there if you are able. Oldspammer 18:21, 26 July 2007 (UTC)
CW vs. pulse (Fourier Transform) NMR is already discussed (OK, not particularly clearly). FT-NMR does not involve pulsing the static magnetic field - it uses pulses of radio frequency to excite a range of NMR frequencies at a given (fixed) magnetic field. Unfortunately most pop science explanations of NMR are pretty bad (see links above). 84.92.241.186 20:29, 4 August 2007 (UTC)
Sorry, but this is something different. In pulsed NMR the sample is placed in constant magnetic field. A short Radio Frequency pulse of suitable duration and frequency is applied to the sample. It excites the nuclear magnetic moments and as they return to their equilibrium state they emit absorbed RF signal that can be collected and analysed. MRI (Magnetic Resonance Imaging) used an extension of this method to look inside your body. Here is a reference [[1]]. TomyDuby 20:51, 12 September 2007 (UTC)
 ? That's a good description of pulse/FT NMR. But surely the point of the previous comment was that pulse NMR is discussed under Fourier Transform NMR and CW NMR is discussed in the previous section? So the original query about the "two modes" is already covered surely? 82.122.56.171 22:17, 17 September 2007 (UTC)

[edit] Nuclear Rabi frequency?

A while ago the following paragraph was added (by an unregistered user) to the article on the Rabi frequency:

"In the context of a nuclear magnetic resonance experiment, the Rabi frequency is the nutation frequency of a sample's net nuclear magnetization vector about a radiofrequency field. (Note that this is distinct from the Larmor frequency, which characterizes the precession of a transverse nuclear magnetization about a static magnetic field.)"

I am only familiar with the Rabi frequency in the context of atomic physics. I've done a quick google search and it is regularly mentioned on pages concerning NMR. I feel that these are two distinct (although possibly analogous) concepts that probably merit separate articles. Does anyone have any thoughts on this?--DJIndica 19:43, 23 October 2007 (UTC)

[edit] NMR Phenomenon?

This article definitely lacks information on the phenomenon of resonance. I personally do not understand this subject fully, especially in the resonance section, where I was hoping to learn about it. In this section, all that is said is the conditions under which "resonance absorption" will occur, leaving many ambiguities. Is the resonance here refering to the emitted photon or the precession of the nuclei? Is the absorption dealing with that of the external electric circuit due to this photon? Is the "correct frequency" something which the experimenter controls or is one that is naturally occurring as a result of precession?

I would really appreciate it if someone took the time to answer these questions in the article. --Wakod2002 (talk) 08:43, 28 November 2007 (UTC)