Talk:Doppler broadening

Correction

I just corrected the formula for the FWHM of the broadened profile, which was wrong by a factor of \sqrt(2).

wrong (old) formula: $\Delta f_{\text{FWHM}}={\sqrt {\frac {8kT\ln 2}{mc^{2}}}}f_{0}$

new formula: $\Delta f_{\text{FWHM}}=2{\sqrt {\frac {2kT\ln 2}{mc^{2}}}}f_{0}$ —Preceding unsigned comment added by Loetknecht (talk • contribs) 17:42, 16 November 2010 (UTC)[reply]

The two expressions you have written here are equal to each other. The new equation in the article is equal to the old equation. PAR (talk) 09:51, 19 November 2010 (UTC)[reply]

Merge

This article should be merged with "Doppler Profile" I've put the notice on the frontpage. --ScienceApologist 23:35, 18 August 2006 (UTC)[reply]

Request for expert in physics

I am a bit confused by the claim that Doppler broadening is going to make Pebble-bed reactors safer. As far as I can tell, Doppler broadening occurs whenever there is U²³⁸, which means it must have occurred in any reactor, including Chernobyl's fourth (if anything, RBMK's have more U²³⁸ than average since they run on natural uranium).

Indeed, Doppler broadening is not mentioned in the Web pages of PBMR, the South African manufacturer: they claim simply that the PBMR is safer because it cannot get hot, never mentioning the word "Doppler". Basically, they claim it is safer because it has a low energy density in the core (and, even if they do not say it clearly, because pebble-bed reactors will be cooled with open air in case of accident. That or a piece of the wall is missing from their diagrams).

So, can any expert tell me whether Doppler broadening can be played with as it is claimed?

Also, it would be nice to know when the effect was discovered. I was reading Schultz's Control of Nuclear Reactors and Power Plants from 1955, and he would only say there was a "negative temperature coefficient" but not its cause.

Add a figure

I think it would be good to include a visualization of a broadened spectral line profile. I had uploaded one previously, but it has since been removed. Here is a link to my figure: [1]. If there are improvements that can be made to it before putting it on this page I am happy to address those! Planetphysicsguy (talk) 20:50, 7 December 2022 (UTC)[reply]

Well, I still do not see any added value in this figure. Something had a certain width and then that something became wider. This is what the "broadening" word means. For somebody not familiar at all with the notion of spectral line, this figure says nothing; for those familiar with the notion, it is trivial. Furthermore, the initial lineshape is already noticeably broad, so you cannot call it "unbroadened" (it isn't a correct English word, BTW). So what is the source of that initial broadening? It would be logical to assume it is the natural width, but then the lineshape should be Lorentzian, while it looks like a Gaussian. Do you want to talk about instrumental broadening? Then the discussion becomes too technical. Finally, "Doppler" is a proper name, so it should be capitalized in any context. Evgeny (talk) 09:47, 8 December 2022 (UTC)[reply]