Talk:Cherenkov radiation

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)

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)

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)

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 V.P. Zrelov,Cherenkov Radiation in High Energy Physics, 1970, widely referred to physics text...

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)

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)

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)