Talk:Compton scattering/Archive 1

Archive 1

Derivation image?

The derivation would be greatly helped by an image showing what was going on (for the visual thinkers among us). For examply, it is very hard to see what theta is, exactly. --jonon 09:33, 2 Jun 2005 (UTC)

I added a diagram and one sentence that clarifies what theta is. --Tim314 22:14, 30 August 2005 (UTC)

Inconsistency in proof

The lambdas are written with apostrophes in the proof, and with indices in the formula being proved. This might be lead to more confusion than absolutely necessary. — Irrbloss 18:40, 16 May 2006 (UTC)

Feynman-Graph wrong??

When looking in the standard textbooks, the Fynman-Graphs (at least the u-channel) looks significantly different then the one presented here!

Look for example in this textbook: Gauge theories in particle physics (CRC Press, 2003)

by Ian Johnston Rhind Aitchison, Anthony J. G. Hey  page 233f

So, if a FG is displayed it should be explained where the t-axis is going and stuff... So its just a pretty picture which says nothing and maybe it is even wrong (I am no expert). —Preceding unsigned comment added by 78.52.237.42 (talk) 13:27, 11 June 2009 (UTC)

The graphs are examples out of a host of possibilities, these ones purporting to refer to electron-positron annihilation. They are are incorrect in as far as one e^- should be changed into e⁺.WMdeMuynck (talk) 09:51, 20 September 2009 (UTC)

I don't see a reference to the compton effect's relationship to redshift. —Preceding unsigned comment added by 99.59.247.92 (talk) 07:17, 1 October 2009 (UTC)

Please?? Redshift is Doppler effect, no interaction happening. IMO far-fetched. -- KlausFoehl (talk) 11:44, 4 November 2009 (UTC)

The two graphs, s-channel and u-channel, could be correct if seen individually, and each having its own time axis directions. But if shown together in context, they are just not consistent. -- KlausFoehl (talk) 11:44, 4 November 2009 (UTC)

Increase in photon energy possible?

Can the photon ever gain energy after the collision? For example, if the electron is moving towards the photon, and the photon is reflected backwards after ejecting the electron, will it have a shorter wavelength and more energy?--SeanMon 23:53, 22 May 2006 (UTC)

Yes, that's called Inverse Compton scattering. It used to be hiding on its own page (at Inverse Compton scattering), but I've just merged the info about it into this article. --Mike Peel 08:56, 2 August 2006 (UTC)

At some point, it might be again worth an own article. There are several applications of Compton scattering off moving electrons. For now I have added a short paragraph on generating high energy photons for nuclear physics experiments, stub quality. -- KlausFoehl (talk) 11:59, 4 November 2009 (UTC)

The formulae are not appearing as they should. This is true for Compton Effect as well.

The Compton effect without photons

Hmmmm.... In J. J. Sakurai's book Advanced Quantum Mechanics ...it looks like the correct wavelength shift and differential cross-section (Klein-Nishina) are derived without quantizing the electromagnetic field...

129.2.175.71 (talk) 21:03, 27 November 2009 (UTC)Nightvid

Compton effect as a double Doppler shift

Kidd, Richard (1985). "Compton effect as a double Doppler shift". Am. J. Phys. 53 (7): 641–644. doi:10.1119/1.14274. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help) This article describes how the Compton effect can be explained by the wave model of light, so it does not provide direct evidence for the photon model. —Keenan Pepper 14:34, 10 October 2007 (UTC)

I don't see the relevance to the article. JFlav 02:16, 28 October 2007 (UTC)

If that article is correct then this article is not accurate when it says "Light must behave as if it consists of particles in order to explain the Compton scattering." and it may be improved by having a Particle Derivation and a Wave Derivation --200.112.183.170 (talk) 22:25, 28 January 2008 (UTC)

Actually, both are correct. Before I cite a corroborating reference for this allegation, let me make a broader point. This is ostensibly an article about Compton Scattering -- sometimes referred to as the Compton Effect. It has great historical significance in the evolution of quantum mechanics, but Compton applied already existing quantum postulates to the resolution of a then existing mystery. Even if his result were wrong -- which it is not -- an encyclopedic article about it would be justified. It is appropriate to refer to seemingly alternative approaches to the same problem, but that should be done only when the editor doing so genuinely knows what he or she is talking about. I do not automatically disparage anyone's understanding no matter their formal credentials, but as a practical matter, "knowing what you are talking about" in this realm tends to correlate with some serious educational credentials in physics. In any case, what the work of Richard Kidd and others touches upon is interpretation -- a fascinating, albeit often philosophical, issue. But, to end these comments, let me quote from a recent book which is available as a google book: 100 years of Planck's Quantum By Ian Duck, E. C. G. Sudarshan (World Scientific, 2000). In chapter II, the authors go through, and quote extensively, papers by Einstein and Compton. At page 89, they interrupt the excerpts to make the following comment: "We omit [from Compton's paper] a lengthy discussion showing that a Doppler shift of the classical radiation from the reference frame of the recoiling electron to that of the laboratory produces the same result. ...The Doppler shift calculation was incorrectly viewed by Bohr as a justification of the correspondence principle description of the the scattering process. We now recognize it as the consequence of applying a succession of Lorentz transformations to the separate absorption and emissions processes -- each of which treats the kinematics in a fully quantum and relativistic way -- which inevitably reproduces Compton's complete result." The Original Compton Paper is Compton, Arthur (1923). "A Quantum Theory of the Scattering of X-Rays by Light Elements". Physical Review. 21: 483. scanyon (talk) 06:30, 4 July 2011 (UTC) scanyon (talk) 23:57, 4 July 2011 (UTC)

concern about error

along the proof comes this equation, I just link the line:

http://upload.wikimedia.org/math/3/8/9/38925d4e4159a20f7b81355cab23f7f8.png

under the root, shouldn't there be index zero with mass? —Preceding unsigned comment added by Quu (talk • contribs) 14:50, 26 December 2007 (UTC)

I understand the comment. $m_{o}$ is frequently found in text books referring to the rest mass or at least mass preceding a Lorentz transformation. In this formulation of a specific problem $e$ and $\gamma$ were chosen as subscripts to distinguish reference to the electron from references to the photons. The dynamic characteristics of the electron before scattering are ignored and it is treated as being at rest as an assumption. Moreover, in any appearance of the electron post-scattering, the transformed mass per se does not appear and everything is expressed in terms of the rest mass. If the transformed (relativistic and post scattering) mass were shown, the other convention already used to distinguish post scattering state from pre-scattering state is to place a prime on the object subscript in which case we would have $m_{e}$ and $m_{e'}$ and again no need for $m_{o}$. The oh or zero subscript is not sacred and would not clarify anything in this context and would conflict with the existing notation which is more than adequate. In Compton's original paper the rest mass of the electron has no subscript whatsoever. — Preceding unsigned comment added by Patamia (talk • contribs) 00:32, 7 July 2011 (UTC)

Introduction

It says "which occurs when X-ray (or gamma ray) photons with energies of around 0.5MeV to 3.5MeV interact with electrons". Doesn't it occor when photons with lower energies interact with electrons, too? Isn't it just that the ammount of wavelength change does not depent on the incoming photons' wavelength and that therefore compton scattering can only be observed if the interacting photons have a high energy!? greetings --Space-Marine 01:05, 17 December 2005 (UTC)

Additionally, it claims that these 0.5-3.5 MeV photons are "medium energy," but then refers to visible light photons as "high-energy," despite the fact that they would be about a million times less energetic than MeV photons. This paragraph needs some work. (Side note: this is my first time editing a talk page, did I do it all right?) 171.66.50.17 22:20, 20 June 2007 (UTC)

In the intro, the line "If the photon has sufficient energy (in general a few eV, right around the energy of visible light), it can even eject an electron from its host atom entirely (a process known as the Photoelectric effect)." implies that Compton effects are more common for energies below those that interact through Photoelectric absorption, which is not true. See, for example, Saha, G.P., Physics and Radiobiology of Nuclear Medicine, Springer-Verlag, pp.55-58, 77-80, 1993.122.107.129.221 (talk) 09:16, 13 April 2008 (UTC)

Overall I think the introduction is too long. There should be a short summarizing paragraph at the beginning describing what it is, who discovered it, and why its important, and the rest of the details should be moved to the rest of the article. All articles should be written this way to conform to wikipedia standards. —Preceding unsigned comment added by 76.65.21.169 (talk) 04:14, 3 March 2010 (UTC)

I have taken it upon myself to begin a revision of what is now the "intro" to the main section. I agree that the article overall lacked focus on the historical and scientific significance of Compton's 1923 paper and have begun to insert this in the intro to the derivation derivation. Eventually, this will be coordinated with revisions to the Introduction proper. This will take a few iterations (citation enhancement will begin with my next iteration). This needs to evolve methodically and adaptively. Some restructuring will certainly emerge. I am a latecomer to this article. Your patience is appreciated and assistance welcomed. scanyon (talk) 06:41, 7 July 2011 (UTC) scanyon (talk) 06:48, 7 July 2011 (UTC)

Importance of Proof

How important is it to have such a long derivation of the Compton formula? I think it would suffice to drop three-fourths of the steps, and instead highlight the fundamental concept that the equation results from conservation of energy and momentum.

BailesB 13:22, 18 December 2006 (UTC)

It's fine to summarize the proof in words, but the derivation itself should remain.

I say this because many authors of physics and math books are content to skip steps in their publications (and I guess that makes sense since every extra page costs money), but Wikipedia isn't made of paper - it can be as long as we want.

And one of the reasons Wikipedia is so valuable is because derivations like this are hard to find in the literature, and it's fantastic that we have an opportunity to finally store and share information like this.JabberWok 03:06, 19 December 2006 (UTC)

Areed. The equations brought me completely through from a minimal reference. I skipped most of it the first few times but they ultametly helped. I wish there were individual reference preference settings.........bat —Preceding unsigned comment added by 24.34.179.180 (talk) 02:49, 1 February 2008 (UTC) the proof can be done in fewer lines, —Preceding unsigned comment added by 174.66.169.51 (talk) 05:34, 21 July 2010 (UTC)

All wiki articles on math and physics involve issues regarding the usefulness and appropriateness of mathematical derivations including the level of detail that is appropriate. Save for a few additional remarks, I won't try to propose general rules and then apply them here. My remarks are, however, germane to the narrow circumstances of this particular article. They are that (1) As is usually the case, what we are talking about here is not a proof in the mathematical sense. It is a derivation which predicts (tentatively) an observable result -- in this case "confirmed" by experiment. (2) The derivation might be made a bit shorter, but it is actually quite good. Compton's original 1923 paper has a much shorter version suitable for a more professional audience, but Wikipedia is not a professional journal and it is no crime if it enlightens someone able to do the math but lacking the subject matter expertise. Perhaps we can slowly tighten it, but (2) as derivations go that involve elements of both special relativity and quantum mechanics, this one is not obtuse and as someone above commented, can be followed well with minimal referencing to supporting concepts. Again, as these things go its quite good. (3) Rather than get into a philosophical argument about it, I would argue that what we should do is accept it as a good derivation (better than most) and capitalize on it. To illustrate this last point, I am going to work on inserting discussion into the article that refers to specific aspects of the derivation to point out some significant historical and physical implications. For example, it can be deduced shrewdly that with respect to behavior of the electron, the photon shift result is relativistically invariant. Although Compton (and whoever provided the derivation in the article) was wise to demonstrate that the result was derivable with special relativity applied to the electron, This is important because it focuses on the fact that the one and only crucial physical assumption (postulate) relied upon is that a quantum of light carries momentum like a particle and not just, as Einstein showed, that the energy of light is quantized. Compton did a lot of good work, but the reason this result remains revered is that it forced the big guns of physics to accept fully that light behaved more fully as a particle than many had been willing to accept. Like a battle in a war, it was decisive. I can use the derivation to highlight this more fully. Without the derivation it would be only so much abstract drivel lost upon even the physics-educated reader. And, by the way, to exonerate myself from POV, I will even cite in the article a well-known text book that makes the same observation <g>. scanyon (talk) 20:53, 6 July 2011 (UTC)

A self-correction! I removed from my prior paragraph the statement “in fact the same exact result follows even if the electron is explicitly treated as non-relativistic.” It is not correct as written, but does refer to an interesting truth. I similarly removed today the allusion to this incorrect statement at the end of the 1st paragraph in derivation section. The real truth is more subtle and I am still pondering whether it should rightly appear in an encyclopedic article. My initial thought about this was stimulated by a comment on the very question in the well known text by Joos on Theoretical Physics. I now think even that comment is slightly misleading. As I ponder whether its appropriate to revisit the point in an encyclopedic article, here is a far better explanation about what is going on. You can do a derivation of the Compton Shift without treating the electron as relativistic. The energy of X-Rays covers an energy spectrum whose width encompasses a high end (hard X-Rays) that has 100 times the energy of the low end (soft X-Rays). Joos, in fact does this, and he notes that there is a reasonable approximation that can be made which is more true at the low energy than at the high energy end of the X-Ray spectrum. That approximation handily produces Compton's full result with no effort. If you bother to numerically plot the result without the approximation, it deviates from the shift (as a percent of the incoming wavelength) very slightly. Specifically, for the softest X-Rays, it is on the order of 1 part in a million overall and approaching zero as the scattering angle approaches 0 (or 2 pi) radians. The curious thing about all this is that a low order approximation can nevertheless reproduce the fully relativistic result valid at all incoming energies! Does this warrant discussion in the article? Maybe not, but if I find a justification for it at all, I can cite Joos rather than my own computations that produce the result. I'll think about it<g>. scanyon (talk) 19:18, 12 July 2011 (UTC)

First Appearance of the Wavelength Change Formula?

The wavelength change formula involving the cosine function doesn't explicitly appear in the May, 1923 Physical Review paper which is dated Dec 13, 1922. Its first published appearance appears to be in Absorption Measurements of the Change of Wave-Length accompanying the Scattering of X-Rays, Philosophical Magazine, vol. xlvi, November 1923, which was dated June 23, 1923. Another paper, The Spectrum of Scattered X-Rays, Physical Review vol. 22 November 1923, also contains the formula and is dated May 9, 1923. --Jbergquist (talk) 08:49, 24 December 2012 (UTC)

Compton used 2sin²(θ/2) instead of 1-cos(θ) in the wavelength change formula in May 1923 Physical Review article although he does their equivalence elsewhere in the article. --Jbergquist (talk) 09:40, 31 December 2012 (UTC)

Is the Electron Momentum Change Inequality Relevant?

The inequality involving the electron momentum change and energy difference just after Equation (1) appears to be irrelevant and I would recommend that it and the related discussion be removed. It doesn't appear to be a significant observation and is somewhat distracting to the flow of the proof. --Jbergquist (talk) 09:51, 31 December 2012 (UTC)

Confusing

This article has no details about the effect and the math formulaes are confusing for the common user, having no meaning. Please add more details in explanation, don't make the article like a short draft for an exam.

i strongly agree with this person! it is full of Math wile i couldn't find any information about the second wavelength coming out from this effect, i know we do have second wavelength but i don't remember how. —Preceding unsigned comment added by Astrosona (talk • contribs) 19:07, 7 April 2008 (UTC)

Another Compton paper, Absorption Measurements of the Change of Wave-Length accompanying the Scattering of X-Rays (Philosophical Magazine, vol. 46, November 1923, p. 899), contains a figure of the scattered x-rays from a graphite target showing two peaks, one associated with the initial x-rays and a second of longer wavelength. In 1924 Compton and Woo showed that the longer wavelength peak was independent of the scattering matterial. --Jbergquist (talk) 23:41, 31 December 2012 (UTC)

Does the figure mislead the reader into thinking the outgoing particles are 90 degrees apart?

File:Compton-scattering.svg depicts the post-collision electron and photon directed at nearly right angles. It was a long time ago, but I remember such a rule, but believe it applied to collisions between identical particles. If there is no rule that says they must be at right angles, it is a bad idea to depict them as such, especially considering that for certain types of collisions (i.e. identical particles) such a 90-degree rule exists. I pose this question because I recently made a new image for the heisenberg microscope at File:Heisenberg microscope with wavefronts and electron scatter.svg and faced the same problem. If anybody remembers their college physics better than I do, please respond. I will be happy to redraw the figure.--guyvan52 (talk) 15:38, 18 February 2015 (UTC)

Elastic or inelastic scattering?

Elastic scattering is energy conserving by definition. Hence, the edit made it inconsistent. The point is, whether you consider only the photon (in which case the scattering is inelastic) or whether you consider the combined system of photon+electron (in which case the scattering is elastic because the total energy is conserved).WMdeMuynck (talk) 04:36, 16 July 2010 (UTC)

Compton limited the 1923 paper to light elements out of concern that for heavier elements the secondary x-rays might not be independent of the electron's binding energy. The statistics clearly favored treating x-ray scattering as a quantum process. --Jbergquist (talk) 00:03, 1 January 2013 (UTC)

This is a recurrent misconception: In fact, according to the very definition in microscopic physics, in inelastic scattering the kinetic energy of an incident particle is not conserved. Peremptory IPs barge in and revert inelastic to elastic to suit their misconception, on a regular basis, alas. (talk) 15:27, 25 October 2016 (UTC)

In Compton scattering, energies of both the photon and the target are conserved in the center-of-mass frame. Hence, it is elastic (as is reverse Compton scattering, naturally). Of course, if one considers only the photon and does so in the lab frame, then one can say it undergoes inelastic scattering; this, however, doesn't make almost any sense since no scattering would be elastic under those definitions. Consequently, there is no such definition in microscopic physics (at least the part of it I am familiar with; I'd like to request sources if someone can prove otherwise) as 'in inelastic scattering the kinetic energy of an incident particle is not conserved', either. This definition (and the Wikipedia article on inelastic scattering that uses it) is rather misleading: it does not specify that one is (as is most commonly done) considering two-particle collisions and that in inelastic scattering the energy is not conserved in the centre-of-mass frame of the two particles (otherwise it is elastic). At the same time the article on elastic scattering has it right (even though it also fails to specify that it only considers two-particle collisions): 'In this process, the kinetic energy of a particle is conserved in the center-of-mass frame, but its direction of propagation is modified'. According to which, again, Compton scattering is elastic. 134.93.132.74 (talk) 15:59, 31 October 2016 (UTC)

Solomonic hair-splitters have addressed your anxieties by using terms like "inelastic scattering underlain by an elastic collision". The Compton effect was observed in the 20s, before particle creation comporting with your center-of-mass definition were around. I fear you are picking a fight with the inelastic scattering article in the wrong place. Yes, the photon loses energy in the lab frame, which centuries of practice had identified with inelastic collisions, even though in the cm (HEP) frame no new species are created. Surely nobody goes to the cm discussing the effect. Compton's paper need not speculate about anything of the sort, so it eschews either term! Rutherford scattering is prototypical elastic. A well-meaning perceptive reader would look at the kinematics and shrug off the cognitive dissonance: an invitation to actually do the kinematics. Clicking on the inelastic scattering link resolves any doubts. Why pretend there is a conceptual issue here? Cuzkatzimhut (talk) 17:06, 31 October 2016 (UTC)

In nuclear and particle physics the notion of "elastic" collisions is that no energy in converted to internal excitation or particle creation. "Inelastic" scattering consists of processes where some initial state energy is converted to internal excitation (such as excitation of a nucleus) or particle creation (such as, say, in pion photoproduction). It does not matter which frame of reference one uses: in both the lab and center-of-mass frames total energy and momentum are conserved, as always. The only useful (and conventional) distinction pertains to whether some of the initial state energy ends up in some other form in the final state. Qwerty123uiop (talk) 21:15, 15 December 2017 (UTC)

I am sorry, you are unilaterally and peremptorily conflating "inelastic scattering" with "inelastic collision" or interaction. The WP article on inelastic scattering stresses the contrast. Think of the elastic electron-quark collision underlying a DIS event. It is not one's first thoughts or tribal background that control; this here is atomic physics. Apologies for reverting your edit, having tried to restore as much of the sound pieces it as I could, which do not touch on your unilateral policy reversal on this, without reaching consensus first. WP is supposed to attenuate confusions, not whip them up. Cuzkatzimhut (talk) 22:33, 15 December 2017 (UTC).

My goodness. There is indeed some semantic hair-splitting going on, both in this article and in the page on inelastic collisions (and its Talk page). It is unwise to introduce linguistic confusion when we really want people to understand the physics of a process. Let us not ignore the standard terminology of the (very large) tribe of nuclear and particle physicists for whom Compton scattering is clearly an "elastic" process because all the initial energy (not just the kinetic energy of the projectile) ends up again in the final state, with no particle creation nor any internal excitation of the participating objects.

You seem to have a strong bias toward what may be the chemists' preferred use of the words "elastic" and "inelastic". But you can be certain that insisting on that usage in this article is not congruent with the usage preferred by physicists for whom Compton scattering is one of the fundamental QED processes. For example, consider the respected and widely-used text "Introduction to Elementary Particles" by David Griffiths, Wiley, 1987, ISBN 0-471-60386-4, pages 15, and section 3.4 starting on page 91. That text proceeds to explicitly compute the Feynman amplitudes for Compton scattering starting on page 235. His usage disagrees with your preferred usage.

I can add that I have already experienced students coming to me, their professor, with confusion about the seemingly-inconsistent usage of the words on the present Wikipedia page.

Therefore, I have a proposed solution. Let this Wikipedia article on Compton scattering not mention the distinction at all. There is no reason to mention it, neither in the first paragraph, nor later in the article. The point of the article is to give readers an understanding of the physical process. To that end, the physics should remain in the foreground, with as much clarity as possible. Of course the article, as presently, must detail the energy and momentum conservation of the scattering process. That was the general thrust of my recent modification: removing the ambiguous-usage word in the first paragraph (plus other fix-ups). I will reestablish those changes absent some really compelling logical counterargument from the community. Qwerty123uiop (talk) 17:05, 17 December 2017 (UTC)

I fear it is not "usage preference". I do appreciate the tribal point (I, myself, being in the HEP subtribe, have witnessed with distaste charged diatribes on DIS, and refereeing work), but you appear insouciant of the semantic wars being waged on this for years and years: and peremptorily strong-arming WP against the extant dozens of editors is not the way to help the world. You certainly cannot adduce Griffith's book on perpetrating the misconception: He religiously uses the term "elastic collision", correctly, which is already emphasized here.

I completely agree with you that the kinematic facts come first---and when students ask me about this I always make them appreciate the facts first, before fussing on nomenclature. I would strongly object to effacing the lede, though. If you wished to be helpful, you might add a salutary footnote about alternate usages, and how they jibe with each community's concerns. Compton's original point was applying relativistic kinematics that upends classical mechanics/freshman-lab expectations about kinetic energy, and to emphasize the transfer of energy to the electron. Solomonic or not, "inelastic scattering underlain by an elastic collision" is not pointless.

The usage has been established, though, and simply effacing it to "reform the world" by WP obscurity is hardly salutary. Repeating correct statements about kinetic energy transfer to the electron in the lab frame but not in the c.m. one, covariant momentum transfer, and frames, with the suitable links, should be helpful. But a unilateral change here at variance with the other WP articles is counterproductive: Students will continue to be confused, and having WP withdraw from being part of the solution is not prudent. Can you propose your footnote here first? This is what the Talk pages are all about.Cuzkatzimhut (talk) 17:31, 17 December 2017 (UTC)

I repeat my suggestion that the lede for the article does not have to include a reference to the apparently disputatious business of how Compton scattering ought to be categorized. Further down in the article there could be a separate short paragraph that states the distinction. As it stands now, about 900 people per day view this article, so this is a matter of some significance. A few points:

1) The length of time this discussion has been going on is immaterial. We can always do better in the clarity with which we express ourselves. If it is an old discussion, maybe that says something important: there really is a problem with how this article is worded.

2) Your comment that the Griffiths book uses the term "elastic" according to your preference is incorrect. Please examine the citation to the book and you will see this. He uses the term according to the HEP and nuclear physics convention. I plan to add it as a reference in this article.

3) You pointed to another Wikipedia page called "inelastic scattering". That page is perhaps also in need of clarification, but that is not my present concern. In that article, however, there is exactly one authoritative external reference, namely to an IUPAC Compendium of Chemical Terminology, a "Gold Book", in which it states: "If in a molecular collision there is transfer of energy among degrees of freedom, but no chemical reaction occurs, there is said to be inelastic scattering." You see the problem? Compton scattering is not in the category of molecular collisions. Thus, the "inelastic" page's sole authoritative reference is not sufficient to support your opinion of standard usage in the case of Compton scattering.

4) The "inelastic scattering" page also has one more link to another Wikipedia page titled "scattering theory". On *that* page we find the following sentence: "The term 'elastic scattering' implies that the internal states of the scattering particles do not change, and hence they emerge unchanged from the scattering process. In inelastic scattering, by contrast, the particles' internal state is changed, which may amount to exciting some of the electrons of a scattering atom, or the complete annihilation of a scattering particle and the creation of entirely new particles." Do you see the issue? This is again exactly the definition that is standard in the HEP / nuclear physics community of what constitutes elastic scattering.

Thus, we see that your preferred terminology is not supported by other information on Wikipedia, the cited references, and the comments of other people (above and elsewhere) on this topic. With these points, it appears to me that we should proceed with the modifications to the Compton page that I propose. I will reestablish the changes, absent some really compelling logical counterargument from the community. Qwerty123uiop (talk) 15:34, 18 December 2017 (UTC)

I insist you are misreading Griffiths: He is only talking about "elastic collisions" and does not touch scattering as used here. He is only emphasizing the scattering species have not changed and you are dealing with the same masses. I am convinced, once your proposed changes are made, you will get prodigious amounts of persistent blowback, and the fussing won't stop. If you feel that strongly in effacing the elastic/inelastic bit from the lede, and at the same time, writing a factually correct section on the point for near the bottom (the title of this here discussion section might serve as that for the article section), I would not object.

But, noblesse oblige: you must propose this section on this page first, to be discussed. Rushing to just slam changes in the article is like writing on sand. Perhaps you have a pithy way of contrasting kinetic energy transfer in the lab frame, the low-energy criterion of inelasticity used here, to the methodologically disjoint usage for c.m. frame kinetic energy conservation. I can tell you from personal experience even Feynman got involved in these arguments concerning electron-quark elastic collisions in "deep inelastic scattering". I am not a partisan proponent of the present usage as you are imprecating, but I have monitored the edit wars on this, and it might not be prudent to rekindle them by ignoring the past... Cuzkatzimhut (talk) 16:00, 18 December 2017 (UTC)

Here is a proposed footnote for the Introduction, not the Lede:

Elastic or inelastic scattering? The photon loses energy in the lab frame, which centuries of practice had identified with inelastic scattering---even though, in the c.m. frame, the respective masses remaining the same, no new species are created and kinetic energy is conserved, the mark of an elastic collision. As a result, HEP and nuclear physicists prefer to emphasize elasticity, while atomic and molecular physicists use "inelastic". Cuzkatzimhut (talk) 16:52, 18 December 2017 (UTC)

I gather that you have been debating this point for some time. If my proposed deescalation of the issue is implemented I predict there will be little to no "blowback". We could continue to discuss Point (2) above, where my position remains that Griffiths' usage of the term is "elastic" in the case of Compton scattering represents a very large community of scientists. You did not comment on my Points (3) and (4), which support the need for a change in the presentation here. Again, at least we need to reframe this issue, removing it from the top line and giving it its own sentence or two of explanation.

I think your idea is good: have a footnote attached to the first paragraph that alerts the reader to the terminology issue. That puts it in a reasonable perspective. You have already supplied a good draft of a text for this purpose. Over the next few days, as time permits, I will implement something, unless you do it first. There are several other text changes I have in mind as well, mainly improved figure captions, inclusion of the Compton formula in energy (rather than wavelength) terms, and citing authoritative texts (probably at least the Griffiths text) for a treatment of the whole Compton story for the reader who wants to go further than this article. Qwerty123uiop (talk) 13:44, 19 December 2017 (UTC)

Yes, I have been trying to calm the waters for a decade, basically. As you see from above, people pick up a fight with the other WP page, on inelastic scattering, with which this has to comport, or else the students start asking the obligatory "is Wikipedia wrong?" question in PSE, etc. It is evident you have not bought the sharp contrast between "inelastic scattering" and "inelastic collision" which finesses (2,3,4); in any case, the last ref of that (i.s.) page seems to represent the molecular beam community, and I don't need to fuss with their practices; maybe you wish to. However, you'd have t ensure that future developments don't lead to a mismatch, the prime handle of troubled students. I started the morphing by keeping mum in the lede, and sticking in the footnote in the intro. I have to remind you, however, that this article is not about Compton collisions in QED, which is sloppy usage adopted to what everyone had grown up with in their educational background in the 40s, but, instead, about early 20th century low energy atomic, resolutely tabletop "lab" physics. Cuzkatzimhut (talk) 15:17, 19 December 2017 (UTC)

References

Magnitude of the momentum

In the article it says: "Note that the magnitude of the momentum gained by the electron (formerly zero) exceeds that lost by the photon:"

Momentum is a vector, not a scalar, meaning that the above sentence makes no sense. This should be removed, and rest rewritten if necessary.

Betaneptune (talk) 00:14, 1 December 2018 (UTC)

? The magnitude of a vector is a scalar. Cuzkatzimhut (talk) 03:54, 1 December 2018 (UTC)

I phrased it wrong. Yes, it's a scalar, but as a scalar it's not a transferable quantity. It's not something that is gained or lost. It is not a conserved quantity, so there's no point noting it.

>>>>> It means nothing in this context. <<<<<

It has nothing to do with the topic and should be removed. It just adds needless complexity. You might as well have said, "Note that Mary had a little lamb."

Betaneptune (talk) 05:17, 1 December 2018 (UTC)

The observation, is, of course, crucial. Of course it is not a conserved quantity--that's the point of the inequality. You may tamper with the verbiage, to your satisfaction (but perorations on kinetic energies in relativistic kinematics are worse than counterproductive), but the math should be there, for the perceptive reader. There is a point! Cuzkatzimhut (talk) 11:21, 1 December 2018 (UTC)

You mean to tell me that this magnitude bit is there to demonstrate that the magnitude of momentum is not conserved? Who ever thought it was? Why do we need this? What would be lost without it? It has nothing to do with Compton scattering. If the point is to demonstrate that the magnitude is not conserved but the vector is, then say that's why this pointless point is there. It makes things more complex than they need to be. It is not part of the derivation. You could also say the magnitude of the distance gained by the photon is more than the magnitude of the distance gained by the electron. This is an equally meaningless statement. Why not put that in there to show how distance isn't conserved? Why not add other things that aren't conserved? Put it in the conservation of momentum article if you must have it. It's not a point of verbiage; it's a meaningless pointless point. Betaneptune (talk) 20:37, 1 December 2018 (UTC)

It is not clear to me whether you are outraged or offended by the verbiage, or by the cold fact itself. You appear to be suggesting the very fact is not salutary to anyone, which plainly isn't so: The question does come up often in students' discussions, as unfortunate babblings on kinetic Energy picked up by the electron have their own way of needing continual stanching. A true hard fact readily available in WP can instruct the reader what is and is not conserved, and what is smaller or larger, and what is transferred or not; and help them with limits, in short, relativistic kinematics, in trying to fit the formulas together. The points are further elucidated in the paragraph following (1), and, of course, inform the entire derivation of formula (2), unless one took pleasure in tripping readers. For a competent reader these are non-issues, and neither I, nor, evidently, you should be reading the article. I have, nevertheless, had direct experiences with confusable students, e.g. in PSE, positively in need of further explanation. Again, the student adept in relativistic kinematics would not be reading this: he would write down the 3 energy-momentum conservation equations (on the scattering plane) for the 4 final unknowns, $f',p_{e}',\theta ,\phi$, and eliminate 3 of them to get the two relations relating θ,φ, to f' ; but you do not appear patient with the other kind. Comparable outrages at popular false proofs of theorems deconstructed have been faced and successfully resisted in WP articles. Once you appreciate the point, really, you might propose your favorite verbiage. I would be more sympathetic if you insisted on demotion to a footnote. In any case, I tweaked the wording to dress up the independent parameter in language that ought to puzzle you less. Cuzkatzimhut (talk) 21:03, 1 December 2018 (UTC)

Well, I guess I got a little too excited. I didn't mean to come across as hostile, but maybe I did. Sorry about that. Anyway . . .

I have never found any Wikipedia science or math article helpful to someone coming to the topic for the first time. They always look more like a reference or summary of every possible facet, no matter how small or insignificant, of the topic at hand. Sometimes it's so confusing it seems like it's useful only for someone who already learned it and just needs a refresher or a reference.

OK, back to this case. I think I see what you're trying to say, but the way it's written now is confusing. Also, when you mark off a phrase by a pair of commas, removing the phrase should not alter the essential meaning of the sentence, nor should it ruin the grammar. Removing ", not simply," changes the meaning to the exact opposite of what you're trying to say! In fact, the entire paragraph needs to be rewritten. Also, the second comma in "After scattering, the possibility that the electron might be accelerated to a significant fraction of the speed of light, requires that its total energy be represented using the relativistic energy–momentum relation," probably needs to be removed. If you remove what's between the first two commas, you get "After scattering requires", which makes no sense. (Yes, sometimes you need the comma for clarity, but I don't think so in this case.) You need a comma between electron and so in ". . . mass of the electron so it is not simply related . . ."

I'd also change

"The change in the momentum of the photon is also, not simply, related to the difference in energy, but further involves a change in direction."

to

"The change of the magnitude of the momentum of the photon is not just related to the change of its energy; it also involves a change in direction."

I don't consider this nitpicking. The way it is now is confusing and possibly lacks sufficient context. I also think it is an unnecessary diversion. I learned the Compton Effect from the book by Gasiorowicz called _quantum physics_. It's online. See pp. 10-12. IIRC, no one in class was confused.

I saw a speaker at a physics colloquium tell us the dangers of the term "relativistic mass". It works fine for a single body in one dimension, but he demonstrated how it just causes confusion in many cases. He said that we should instead simply say that the relation between energy, (rest) mass, and momentum (E^2 = m^2 + p^2) is simply different in relativity. I'm not sure if that applies here, and I don't have the time to check. There is a pretty good discussion of energy having inertial mass in relativity in Einstein's book _Relativity: the special and the general theory_ (also online). That doesn't completely cover the situation here, but I think it's important to read, because it clarifies the energy/mass bit, which is confusing to many. See chapter XV. Betaneptune (talk) 16:11, 2 December 2018 (UTC)

OK, tweaked the verbiage to probably comport with your suggestion. Indeed, specific changes proposed is what this page is all about. Also indeed, "relativistic mass" has no place anywhere, and "rest mass" is superfluous for "mass" -- Okun rightly felt strongly about that. Of course this is not how I would have written this lumbering stretch myself. Simple nondimensionalized algebra of the 3 relations, $(f,f,0,0)+(m,0,0,0)=(f',f'\cos \theta ,f'\sin \theta ,0)+({\sqrt {m^{2}+p^{2}}},p\cos \phi ,-p\sin \phi ,0)$, would immediately get to the point, (3,4), in 2 lines, which is how any particle physicist would quickly settle all; but, traditionally, this is an illustration vehicle for novices to leave classical mechanics behind them and move on to simple relativistic kinematics. The original editor apparently believed this is an explicit annotation of Compton's discussion. In any case, you are right that this, and WP in general, is not an introductory tutorial or a substitute for a textbook. There is Wikiuniversity for that. It is more like a review crib sheet and supplement to an obscure article. Cuzkatzimhut (talk) 18:00, 2 December 2018 (UTC)

Inverse Compton scattering vs. Compton backscattering

Are these two terms synonymous, or is one a special case of the other? — Preceding unsigned comment added by 216.46.157.123 (talk) 22:27, 2 December 2018 (UTC)

Is it unclear in the lede? Inverse Compton scattering occurs when a charged particle transfers part of its energy to a photon. Inverse Compton scattering is the same type of amplitude, except the net transfer of energy is from the charged fermion to the photon, and not vice versa. Cuzkatzimhut (talk) 00:59, 3 December 2018 (UTC)

But are the terms Inverse Compton scattering and Compton backscattering synonyms? 216.46.157.38 (talk) 06:42, 5 December 2018 (UTC)

Yes. Backscattering is preferred when the direction of the photon is roughly reversed, upon impact with an ultrarelativistic electron. The process is inverse Compton, though. Typically, laser photons of a few eVs backscatter to MeV such. Cuzkatzimhut (talk) 11:53, 5 December 2018 (UTC)

Inverse Compton scattering in Gamma Ray Burst events

Recent publications indicate ICS is the mechanism producing TeV photons by scattering x-ray photons off of GRB electron jets that are moving at 0.9999c:

Evgeny Derishev et al. The Physical Conditions of the Afterglow Implied by MAGIC's Sub-TeV Observations of GRB 190114C, The Astrophysical Journal (2019). DOI: 10.3847/2041-8213/ab2d8a

A very-high-energy component deep in the γ-ray burst afterglow; The H.E.S.S. collaboration; Nature, 2019; DOI: 10.1038/s41586-019-1743-9 , https://nature.com/articles/s41586-019-1743-9

Teraelectronvolt emission from the γ-ray burst GRB 190114C; The MAGIC collaboration; Nature, 2019; DOI: 10.1038/s41586-019-1750-x , https://nature.com/articles/s41586-019-1750-x

Observation of inverse Compton emission from a long γ-ray burst; The MAGIC Collaboration; Nature, 2019; DOI: 10.1038/s41586-019-1754-6 , https://nature.com/articles/s41586-019-1754-6

Fascinating stuff. LeadSongDog come howl! 18:04, 21 November 2019 (UTC)

recat

I moved the article from Category:Physics to Category:Quantum Mechanics to alleviate overcrowding. StuTheSheep 03:11, Mar 23, 2005 (UTC)

I moved the article from the heading "Compton efect" under the heading "Compton scattering". The last one is more often used. --Eleassar777 15:13, 30 May 2005 (UTC)

In articol nu se spune ca factorul h/(m_e*c), numit constanta lui Compton, este de fapt lungimea de unda a fotonului gama de la anihilarea electronului cu pozitronul. Pentru verificare se poate folosi relatia pentru constanta de actiune h=(k*Qe*Me)/(De*Ffae). Unde k=9*10^9 (N*m^2)/C^2, Qe=1,602*10^-19 C, Me=9,109*10^-31 Kg, De=Re/(2*pi^2*k), Re=2,81743*10^-15 m. Ffae=1,23726*10^20 Hz. Si pentru sarcina electrica elementara se poate folosi relatia Qe=(c^2*De)/k 2A02:2F0B:870F:CF00:84B6:4A46:8BE1:653A (talk) 08:49, 21 June 2020 (UTC)

Error in Derivation

Article claims The derivation which appears in Compton's paper is more terse, but follows the same logic in the same sequence as the following derivation

Compton's paper - PhysRev.21.483 - has relativistic momentum used in his derivation - see Compton's equation (1) from his paper which incidentally has a typo in the cosine rule formula - the cosine term should be negative.

Thus the vector momentum equation used in this article should have a gamma multiplying the electron momentum, which in turn means that equation (2) should have gamma-squared multiplying the left hand side.

Basically, you cannot have relativistic energy without relativistic momentum, so although the math of the article gives the correct formula for Compton Effect is does not represent the physics.

This would explain why Youtube videos are also incorrect, they seems to be sourcing the derivation from this Wiki JohnWki (talk) 13:17, 2 March 2022 (UTC)