Talk:Čerenkov radiation

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[edit] Glow

This article states that "even very radioactive substances do not glow in air"; on the other hand. polonium claims, supported by LANL [1], that polonium does glow blue in air "by excitation of the surrounding air". Is this a different glow, or is this article wrong? --Andrew 18:07, Dec 16, 2004 (UTC)

Upon further research, a number of radioactive substances definitely glow (see the CRC handbook; eg. polonium, promethium, and radium). So I took out the claim:

The Cherenkov effect is used as a visual cue in Hollywood movies to announce radioactive materials. However, it should be noted that even very radioactive materials do not glow in air - the particles are simply too slow - and that even in water a source may be producing a dose of radiation lethal in seconds without easily visible Cherenkov radiation. A source itself would only glow if it was very strong, transparent, and an insulator.
I wrote that working from the basis that a particle would only produce a Cherenkov effect in air if it was faster than the speed of light in air (meaning it'd have to be at a highly relatavistic speed). This may be a misunderstanding of the physics involved on my part, however. In any case, we should probably note that the glow cannot be counted on to identify a (perhaps dangerously) radioactive object. I'd also note that "excitation of the surrounding air" could refer to excitation of electrons in air, by passing particles, which then produces light when the electrons return to the ground state. This is different from Cherenkov radiation. Pakaran 00:18, 29 Apr 2005 (UTC)

I suspect that the ionization of air is what causes the blue glow of highly radioactive materials (see criticality accident). A beta particle would have to have about 6 MeV of kinetic energy to produce Cerenkov glow in air (rest mass is 0.511 MeV, refractive index of air is about 1.003); radium gives about 0.046 MeV. --Andrew 03:30, Apr 29, 2005 (UTC)

[edit] Heaviside's prediction

Should we mention that Cherenkov radiation was predicted by Oliver Heaviside in 1888-1889?

Absolutely: in standard practice (calling an effect after the one who predicted it, starting with Halley) it would even be called Heaviside radiation. Thus it should be mentioned in the leading paragraph. Harald88 17:02, 22 March 2006 (UTC)

[edit] Explicit definition

This may seem like an obvious question to those who are technically acquainted...

You say that the absence of Cherenkov radiation is not a sure sign of the absence of dangerous levels of radioactivity, but could it be said that the presence of Cherenkov radiation is a sure sign of the presence of dangerous radioactivity? --68.107.141.30 00:52, 25 December 2005 (UTC)


Yes, it's true that the presence of the Cherenkov's Radiation means that -to put things simply- you're in big trouble. But only if you are in the same medium as the one in which the radiation occurrs or and similiar and close to the source. If you're in a medium which stops the radiation then it's, of course, stopped. For example: imagine Cherenkov's Radiation occurring in a place fully isolated from the outside -- you're safe outside as long as the isolation is not destroyed. Isolation can anyting that doesn't meet the requirements for the radiation to take place. Another example: It's much harder to produce the radiation in the air than it is in water. If you produce weak radiation in water then you can make it powerful enough for it to visible in water, but at the same time weak enough for it to be harmful in air. Then, you'll be able to actually watch it, standing next to the water pool. —Preceding unsigned comment added by 83.142.107.30 (talk) 23:14, 6 April 2008 (UTC)

[edit] Tscherenkov / Cherenkov

In the Science and technology in the Soviet Union article, the name is spelled as Tscherenkov (assuming it's the same person). Should there be a redirect from Tscherenkov radiation to Cherenkov radiation? Googling suggests this is the german spelling of the name. --129.240.122.183 22:35, 26 January 2006 (UTC)

Sure, why not? Done. -- Xerxes 04:17, 27 January 2006 (UTC)
This is a small point but it's noteworthy: while the man's name is Cherenkov, the phenomenon is called Cerenkov Radiation (without the 'h'). I've never seen it spelled with an 'h' in any physics text. But this is a small point. Astrobayes 22:23, 29 June 2006 (UTC)
See Pavel Alekseyevich Cherenkov for further discussion. The guy's name was "Черенков", not any of the above. The current standard transliteration would seem to be "Cherenkov", but transliterations have been known to change over the years. "Čerenkov" does appear to dominate in science, but what that indicates is questionable. Probably it means that it was the favored spelling of someone who wrote a notable book. If someone is interested and has a lot more free time than I do, it would be a nice thing to track down. :) Andrew Rodland 22:28, 17 July 2007 (UTC)
See V.P. Zrelov,Cherenkov Radiation in High Energy Physics, 1970, widely referred to physics text... —The preceding unsigned comment was added by Stuart Ponder 63.199.162.164 (talk) 08:54, 5 December 2006 (UTC).

In Russian Language does not exist letter -Č-, there it is -ч-. This way of writing -ch- comes from Czechoslovakia, and a couple of other balkan states. Probably the original article that this name was taken from was written by a Czech person. The sound that you are looking for (-ch- in English) is written the same way you write it in English language, namely -ch- (if you translate from Cyrillic alphabet into Latin, that is). The reason why, sometimes, you come across a -TCH- variation of it, is because in Russian language the sound -ch- is a shorter(!) AND "tougher"/stronger sounding -ch-. I.E. think of the Chicagoans (in the States) pronouncing the name of their city (Chicago), well, now make it, (the -ch-), sound "shorter" and sharper. That would be the difference in pronunciation. It is NOT a German way of spelling it. You see, there is no set standard in Russia how to write some of their sounds, that is why you get to see so many variations of spelling of the same sound. Eg.: Russian name Сергей, can be written as Sergei, Sergey, and Serguei, but in each variant it sounds the same. English language has 26 letters, Russian has 33. The sound -sh- is -ш-, however, you can come across -sh- way of spelling it almost as much as -sch-. Sound -я- can be written as -ya-, -ja-, and -ia-. Russian name Ваня, can be written as -Vanya- and -Vania-. Яблоня as -jablonya- (apple tree), and so on and so forth... So, you can send that link from Tcherenkov to Cherenkov with an easy heart. (And for the love of god, folks, remove this -Č- from his name in this one. This is the very reason I even got here in this discussion to let you know. It almost lookes like... blasphemy(?) the more I look at it). :) I'm sure the dude who created it meant well, it's probably that he used a Czech source for reference, or something. - Regards. :) —Preceding unsigned comment added by 128.205.115.91 (talk) 02:03, 6 March 2008 (UTC)

[edit] Superluminal?

Could someone explain in the article what's meant by "faster than the speed of light in the medium"? I thought the speed of light was a constant, and nothing could go faster than it?

Nothing can go fater than Light in vacuum, however, you can go faster than light in a medium (like water or glass) because light is slowed down. --Falcorian (talk) 03:42, 25 March 2006 (UTC)
If you want a straightforward answer, consider this: The speed of any electromagnetic wave is, to first order, v = c/n, where n is the medium's index of refraction, c = 3*10^8 meters/sec.squared. For vacuum, n=1 so the speed of light (which is an electromagnetic wave) is v=c. Nothing can exceed that speed. But, for many material media n>1 so then v<c and light in that medium travels slower than light in vacuum. It is therefore possible for something traveling faster than this speed to exceed the speed of light in that medium. Astrobayes 22:27, 29 June 2006 (UTC)

[edit] Luminal boom

Should I add "sometimes this is refered to as a "luminal boom" - because I've heard that before. 68.6.112.70 08:16, 17 April 2006 (UTC)

Generally, made-up words and phrases should not be added to articles. The analogy to sonic booms is already in the article. -- Xerxes 15:54, 17 April 2006 (UTC)
Where have you "heard that before?" If you cite a verifiable source, then what you're saying would carry some weight behind an edit or addition. If not, then it's probably best to leave this phrase out as it would be more likely to garner a revert. Astrobayes 22:30, 29 June 2006 (UTC)

[edit] Definition

The definition mentions that this effect is when a "charged particle" goes through an "insulator". However, I would think that this effect should occur when ANY particle (charged or not) passes through ANY medium (inulator or not) at faster than the propogation speed of photons in that medium. 68.6.112.70 08:18, 17 April 2006 (UTC)

You're wrong about charged particles; a neutral particle has no impact on the electromagnetic fields inside the medium, so it cannot produce radiation. The bit about conductors is already explained in the article: no light is produced. -- Xerxes 15:54, 17 April 2006 (UTC)

[edit] Accelerating 'matter' beyond speed of light.

"Colloquially and in chemistry, matter is easy to define because it is directly associated with mass." [[2]]

I think the use of the term 'matter' in the following sentence in this article on Cherenkov radiation is misleading: "Matter can be accelerated beyond this speed [the speed of light] during nuclear reactions and in particle accelerators."

The problem is that 'real', 'physical' matter can NOT be accelerated beyond the speed of light. Only theoretical particles like Tachyons (which do not have any mass) can go beyond the speed of light. 'Matter' suggests real particles with real mass, hence it is misleading. The problem of course is the loose definition of matter, but in this instance i think it pays to be pedantic since not going beyond the speed of light is a fundamental rule we all learn in physics class!

Instead i would suggest something like the following: "Certain special particles can be accelerated beyond this speed during nuclear reactions and in particle accelerators."

--Kavrod 14:46, 8 January 2007 (UTC)

I disagree. It says: "For example, the speed of light in water is only 0.75c. Matter can be accelerated beyond this speed during nuclear reactions and in particle accelerators." which is true. Matter can be accelerated to faster then 0.75c in water. Further, it says right after that "Cherenkov radiation results when a charged particle, most commonly an electron, exceeds the speed of light in a dielectric (electrically insulating) medium through which it passes." Matter can't break 1c, but it can certainly go faster than the speed of light in certain mediums. --Falcorian (talk) 18:05, 8 January 2007 (UTC)

[edit] the angle is not 90 degrees.

The figure shows an 90 degree angle between wavefront and emission angle. Note that the pysical light front of photons are not in 90 degree angle with the emitted light. This i due to the difference between group and phase velocity. Read for example http://arxiv.org/abs/hep-ex/0008001 —Preceding unsigned comment added by 130.237.208.86 (talk) 13:28, 4 November 2007 (UTC)

[edit] Image change?

Just being proper and asking first, but I think we should change the current image with this one to the right. I feel it illustrates the phenomenon more obviously (for lack of a larger vocabulary). Any thoughts? --RA dialogue observe 06:14, 14 December 2007 (UTC)

There has been no answer for a few days, so I'm just going to assume no one cares and change the image already. --RA dialogue observe 07:06, 19 December 2007 (UTC)
I missed it the first time, but no, no problem at all. New one looks good! --Falcorian (talk) 16:26, 19 December 2007 (UTC)