Talk:Rutherford scattering experiments

Why the Thomson model was wrong

@Johnjbarton: A week or so ago you complained that the material I put on the Thomson model was wrong somehow. I think we should do a section on it, and I invite you to lay it out, since you understand the history better. Kurzon (talk) 18:14, 30 July 2024 (UTC)

Our treatment of the case against the Thomson model is spread out in the article. It is discussed in "Legacy", "Comparison to JJ Thomson's results" and some implicit parts of the experiment. Perhaps we need to rearrange the content to address the Thomson model head on.

I am opposed to a mythological discussion of how the Rutherford experiments devastated Thomson's model. It's not what happened. That's half the reason I'm against a scattering theory section on Thomson model; the other half is its distraction from the article main content.

Rutherford's scattering model deposed Thomson's scattering model, but the physics community did not understand the power of scattering models at the time. So the implications for atomic models did not sink in. In addition, Rutherford's atomic model had no electrons, it's not a replacement.

Do you think it would help to subdivide the Legacy section into "Particle scattering" and "Demise of the Thomson model"? That would draw attention to the two aspects and give them focus. The latter section could include more modern perspective. Johnjbarton (talk) 18:45, 30 July 2024 (UTC)

Let me study the matter a little further until I fully understand what you're talking about. Kurzon (talk) 11:33, 31 July 2024 (UTC)

Page 19:

• Kragh, Helge (2012). Niels Bohr and the Quantum Atom: The Bohr Model of Atomic Structure 1913–1925. Oxford University Press. ISBN 978-0-19-163046-0.
• "Shortly later Thomson’s picture of the atom faced a new and grave difficulty, namely its inability to explain the scattering experiments with alpha rays performed in Manchester by Hans Geiger and Ernest Marsden under Rutherford’s supervision (see Section 1.5). Although these experiments were highly important, the demise of the Thomson atom was not simply caused by them. The refutation of the classical Thomson process was a gradual process, during which anomalies and conceptual problems accumulated until most physicists, including Thomson himself, realized that it could not be developed into a satisfactory state."

Johnjbarton (talk) 01:37, 2 October 2024 (UTC)

Right... if the electrons circulate in the positive sphere, shouldn't they lose energy to electromagnetic radiation? Kurzon (talk) 06:47, 2 October 2024 (UTC)

No.

• Wheaton, Bruce R. (1992). The tiger and the shark: empirical roots of wave-particle dualism (1. paperback ed., reprinted ed.). Cambridge: Cambridge Univ. Press. ISBN 978-0-521-35892-7.

Page 113

• "In the article in which Larmor derived expression 5.5, he went on to suggest that radiative losses might drop almost to zero for atomic systems with more than one electron. This would be true as long as the vector sum of all electron accelerations remains zero, a situation most easily achieved when two electrons describe the same circular orbit at opposite ends of a diameter. J. J. Thomson developed this idea in 1903 for radiation from multi electron orbits, finding that the energy radiated per electron drops by a factor of roughly 1,000 for each additional electron in the ring when the particles move at a velocity of 0.01c."

Johnjbarton (talk) 16:13, 2 October 2024 (UTC)

YouTube video

This just happened to pop up on my YouTube feed this evening: How Rutherford Split the Atom for the First Time https://www.youtube.com/watch?v=dHrX1U7KCis RoySmith (talk) 01:07, 10 September 2024 (UTC)

A very nice video with only a couple of minor (and typical) errors.

These later experiments are covered to some extent on Proton#History and Ernest Rutherford. You could add the video as an External Link to one of these.

I originally thought to extent the Experiments section here this article is focused on Rutherford's discovery of the atomic nucleus. In fact I wonder if we should change the name of this article to "Discovery of the atomic nucleus". Johnjbarton (talk) 03:23, 10 September 2024 (UTC)

What are those minor errors? Kurzon (talk) 08:03, 10 September 2024 (UTC)

Near the beginning the video describes Rutherford's atom as having orbiting electrons, but that was Bohr's work. Near the end Wilson's cloud chamber is invented around 1919, but in fact it was in use in 1911. The details of the "whose first" bits are I believe a bit disputed but I've not read up on that. Minor stuff, the video is excellent. Johnjbarton (talk) 14:59, 10 September 2024 (UTC)

A new section which is not correct.

I have deleted most of a paragraph in "Scattering theory and the new atomic model". It starts with an assertion of contrast without meaning:

• At the atomic scale, the concept of "solid matter" is meaningless,

This is misleading because the nature of the forces does not change with scale. High speed alpha particles penetrate "solid matter" just like they penetrate atoms.

• the alpha particle will not bounce off the atom ...According to Thomson's calculations,

Thomson says nothing about alpha particles bouncing or otherwise, see

• Heilbron, John L. (1968). "The Scattering of α and β Particles and Rutherford's Atom". Archive for History of Exact Sciences. 4 (4): 247–307. doi:10.1007/BF00411591. ISSN 0003-9519. JSTOR 41133273. Page 277
  • "He unveiled the new approach on February 21, 191O, in a paper delivered to the Cambridge Philosophical Society under the title, "The Scattering of Rapidly Moving Electrified Particles." The title is in fact quite misleading: Thomson did not consider α particles, nor did he take loss of speed into account, as Wilson's results required for a general treatment; the new theory therefore applied only to the deflection of β so thin as to make the velocity degradation negligible."

By the way, Thomson viewed the alpha particle as an atom, on the same scale as say gold atoms, not as a charged particle on the same scale as beta particles.

I also do not think this section is needed: what problem does it solve? Johnjbarton (talk) 15:29, 17 September 2024 (UTC)

I watched a video by Neil DeGrasse Tyson which described the Rutherford experiment. He says that Rutherford discovered that matter was mostly empty because almost all the alpha particles went through the gold foil as opposed to all of them bouncing back like a mirror reflects light. I wanted to clarify that he always expected all of the alpha particles to go through, he didn't expect a few of them to be reflected back. Kurzon (talk) 15:38, 17 September 2024 (UTC)

It is true that Rutherford was "surprised" by the backscattering in some way, because through out the 1900's decade he was learning new things about alpha particles. Everything was a surprise. But you have to ask yourself: why did Rutherford recommend Marsden's reflection experiment? Rutherford clearly knew by the time of the 1908 experiment that alpha particles do not obey the expectations set by Thomson's model. Recall that these are very tedious experiments, so much so that Rutherford himself was unable to complete them. These people were not just trying reflection for the fun of it. The evidence shows that from 1905 on they were trying to understand why some alpha particle scattering was contrary to the existing model. The reflection results were absolutely unexpected, but not by Rutherford: he chose to do the experiment to look for the effect.

But this is not related to the text I deleted. That text was about Thomson and calculations that he did not do. Johnjbarton (talk) 03:45, 18 September 2024 (UTC)

https://youtube.com/shorts/iVpRtVJ5Uys?si=5IOmIE7m4b47hMKK Kurzon (talk) 16:05, 17 September 2024 (UTC)

I don't want to mislead readers, rather I want to lead them away from the simplistic descriptions they were taught in high school. I see a lot of videos on YouTube by Indian professors that do not do justice to the history. Kurzon (talk) 18:06, 17 September 2024 (UTC)

Ok so I just told the non-simplistic story in a different and more historically accurate way. Johnjbarton (talk) 15:56, 18 September 2024 (UTC)

Put plum pudding stuff here

I don't feel like this article is complete if the plum pudding stuff isn't here. That's like half the story. Kurzon (talk) 15:28, 25 September 2024 (UTC)

I don't agree and I don't think it's a close call.

• The article topic is the Rutherford scattering experiments. Rutherford's 1911 paper is relevant because it provides a model to explain the scattering experiment results. The Thomson scattering theory was designed to explain beta scattering. There is no evidence that Thomson ever expected his scattering theory to apply to Rutherford's data.
• If we want to say more about the plum-pudding model, then the best place to start is more discussion in Plum pudding model of the beta experiments.
• The content you describe as "plum pudding stuff" already exists in Plum pudding model, so you are essentially merging. I think we have two strong balanced articles. Taking content from one and putting here just makes this one too long and that one too weak.
• Details of Thomson's scattering model are important in the context of the beta experiments, Thomson's model, and the times represented. But after the Geiger-Marsden result, the details are not helpful because its clear that the model does not work. That is why Rutherford starts his 1911 paper with the quick calculation on turning alpha particles.
• The article already has two sections of details on scattering models. Don't think readers need more, especially when the content is available in one click.

Johnjbarton (talk) 16:12, 25 September 2024 (UTC)

• Rutherford cites Thomson's equations in his 1911 paper. That's the connection.
• I'm not merging, I'm repeating, or perhaps doing a partial transfer.
• The details help students understand the reasoning behind the plum pudding model's demise. It's there for historical reasons. This article is a history article.
• I'll delete the section based on the Hyperphysics site. It's redundant.

Kurzon (talk) 16:49, 25 September 2024 (UTC)

• Rutherford's discussion of Thomson's equations is similar to what we have now; his citation is comparable to our wikilink. Rutherford does not reproduce Thomson's derivation and neither should we.
• The content needs more context (beta scattering issues) which can be added in its current location.
• I object to the concept that Thomson's analysis is primarily valuable because it was "wrong". It was justified by the evidence of the time. Students can read the plum pudding model for both the detailed model and its historical context. The role of beta scattering on motivating Thomson's model should be covered in Plum pudding model. In this Rutherford article we can do many different things to improve the historical accuracy. For example this article over emphasizes the intensity vs angle data but historically the thickness and material dependence were just as important (the angle data was not very good until 1913).
• The second scattering model based on the Beiser reference is helpful for students as you previously discussed not being familiar with the scattering from a central potential assumed by Rutherford's approach.

Johnjbarton (talk) 18:14, 25 September 2024 (UTC)

• Thomson's model became wrong after Rutherford's alpha scattering evidence came in. If we want to show how the model was correct before that, we can certainly go into detail in the plum pudding model article.
• Once I brushed up on hyperbolic geometry, I edited your write-up to make it more accessible, filling in some gaps in your explanation. I believe it is now adequate.

Kurzon (talk) 19:30, 25 September 2024 (UTC)

@Headbomb and Materialscientist: Would you guys care to comment? I think this article needs to take a look at the plum pudding model to complete the story. It doesn't have to be as detailed as the plum pudding article itself, it just needs the maths. Kurzon (talk) 21:36, 25 September 2024 (UTC) @Headbomb and Materialscientist: Take a look at my revision and tell me what you think. https://en.wikipedia.org/w/index.php?title=Rutherford_scattering_experiments&oldid=1247703064 Kurzon (talk) 14:26, 26 September 2024 (UTC)

I agree the plum pudding stuff needs to be there. Literally every introductory textbook on the subject matter contrast Rutherford with Thomson. Explaining what Thomson model predicted and how it fails to account for large angle deflection is critical. Headbomb {t · c · p · b} 16:24, 26 September 2024 (UTC)

The article already contrasts Rutherford and Thomson models:

• Rutherford_scattering_experiments#Thomson's_model_of_the_atom
• Rutherford_scattering_experiments#Alpha_particles_and_the_Thomson_atom
• Rutherford_scattering_experiments#Scattering_theory_and_the_new_atomic_model
• Rutherford_scattering_experiments#Alpha_particle_reflection:_the_1909_experiment
• Rutherford_scattering_experiments#Rutherford's_Structure_of_the_Atom_paper_(1911)
• Rutherford_scattering_experiments#Comparison_to_JJ_Thomson's_results

The proposal by @Kurzon is to included a detailed presentation of Thomson's beta scattering theory.

@Headbomb Can you cite some text books that present Thomson's beta scattering theory? Johnjbarton (talk) 16:54, 26 September 2024 (UTC)

I don't have my textbooks with me, but Hyperphysics has the relevant math. Headbomb {t · c · p · b} 17:04, 26 September 2024 (UTC)

The reference used by the Hyperphysics site for Rutherford scattering is the Beiser textbook. That was the basis for our section "‎An alternative method to find the scattering angle". That section was deleted without an edit summary by @Kurzon.

The Hyperphysics site coverage of Rutherford scattering does not include the 1910 beta scattering paper of Thomson. That is the content being proposed now.

If I understand correctly, @Headbomb would support the addition of the content similar to Hyperphysics, which is "‎An alternative method to find the scattering angle" content, not the beta scattering content I oppose. Johnjbarton (talk) 16:13, 27 September 2024 (UTC)

I deleted the Hyperphysics stuff because it was redundant. Kurzon (talk) 08:24, 29 September 2024 (UTC)

It was not redundant. Johnjbarton (talk) 17:54, 29 September 2024 (UTC)

But you end up with the same formula. Kurzon (talk) 18:14, 29 September 2024 (UTC)

Beiser's book does a simplistic mathematical description of scattering in the Thomson model, then it goes into the Rutherford model. Before Johnjbarton came along, that's what this article did, and it lacked Rutherford's scattering model. Thanks to Johnjbarton we now have both, and makes sense to have both in this article. I don't propose eliminating the plum pudding model article, I just want to copy the maths stuff. Kurzon (talk) 17:48, 26 September 2024 (UTC)

Recent addition has serious errors.

The content added in this edit has many errors. I started to correct them but this content is in my opinion inappropriate for this article per the ongoing discussion on the topic #Put plum pudding stuff here. So rather than invest a lot of time correcting this I will just annotate it. Johnjbarton (talk) 03:18, 27 September 2024 (UTC)

I gave up even commenting. Johnjbarton (talk) 03:37, 27 September 2024 (UTC)

Hey I am glad you're paying attention. Since I copied this stuff from the plum pudding article, that article always had these errors and they're finally getting fixed. Kurzon (talk) 04:18, 27 September 2024 (UTC)

So you added content you knew was incorrect. Johnjbarton (talk) 16:20, 27 September 2024 (UTC)

There's always errors that escape my notice. Kurzon (talk) 16:30, 27 September 2024 (UTC)

Best notation for mean of a square root?

What's the best notation for expressing the mean of ${\sqrt {L}}$? Would it be ${\overline {\sqrt {L}}}$ or perhaps $({\sqrt {L}})_{\mu }$ Kurzon (talk) 05:08, 27 September 2024 (UTC)

Comments

@Tjlafave: What do your students think of this article? Kurzon (talk) 10:49, 29 October 2024 (UTC)

Scientific context for Rutherfords work

I want to explain why I reverted a change by @Kurzon. Many of our articles suffer from a weird kind of "hero worship" in which the accomplishment of one person are described but the input from all others are omitted. So claiming the "Rutherford knew" does not represent the nature of the science. Rather than deleting information about how "Rutherford knew" we should be seeking out sources to document how he knew it. Johnjbarton (talk) 18:33, 24 November 2024 (UTC)

I guess we've sorted this out, but it's just another example of how much extra work you create by not including edit summaries. If this edit, which has no summary, had said "Thomson and Rutherford found that alpha rays ionize air in 1898" then I would not have reverted the edit and you would not have gotten mad and I would not have to post this topic. Johnjbarton (talk) 19:24, 24 November 2024 (UTC)