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Cherenkov Radiation

iaea.org

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Re: Cherenkov Radiation

#31

Post by voidUpdate »

freitzzz wrote: post #18

Not a science guy per se, is this blue the same blue in the radioactive accident in Goiânia’s?

According to the all-knowing Wikipedia, "The exact mechanism by which the blue light was generated was not known at the time the IAEA report of the incident was written, though it was thought to be either ionized air glow, fluorescence, or Cherenkov radiation associated with the absorption of moisture by the source; a similar blue light was observed in 1988 at Oak Ridge National Laboratory in the United States during the disencapsulation of a caesium-137 source"

Re: Cherenkov Radiation

#33

Post by margorczynski »

I think a problem is that because of historical reasons the speed of light is used interchangeably to something much more fundamental - the maximum speed at which information can propagate in space. Which is of course the speed of light in a vacuum but a better approach is the inverse - light in a vacuum moves at the maximum speed possible in our universe.

Re: Cherenkov Radiation

#34

Post by JumpCrisscross »

prathje wrote: post #15

It took me a long time to develop an intuition for light and electromagnetic wave propagation, and I’m still working on it. Fundamentally, changes in the EM field propagate always with the speed of light in a vacuum, i.e., c (also known as the speed of causality). Single EM waves propagate with exactly this speed and they do not magically slow down in a medium... they propagate happily at speed c! (FYI EM waves are m…

> changes in the EM field propagate always with the speed of light in a vacuum, i.e., c (also known as the speed of causality)

Speed of causality is a way more intuitive term.

Massless particles travel at the speed of causation in a vacuum. (Usually. Someone else brought up solitons.) Not necessarily in a medium. Trying to work backwards from speed of light to gravity propagating is tortured; understanding that gravity can't cause an effect faster than causality itself is more direct.

Re: Cherenkov Radiation

#35

Post by smnplk »

prathje wrote: post #15

It took me a long time to develop an intuition for light and electromagnetic wave propagation, and I’m still working on it. Fundamentally, changes in the EM field propagate always with the speed of light in a vacuum, i.e., c (also known as the speed of causality). Single EM waves propagate with exactly this speed and they do not magically slow down in a medium... they propagate happily at speed c! (FYI EM waves are m…

I dont think there can be intuition for this. How can one even imagine an electron "flying" through space, there is no measurable thing that travels, we can only see the disturbance of the surrounding space caused by it. But what is the it, does it maybe live in other dimension not accessible to us, or is there no it at all ? I gave up as a layman trying to understand any of this. Sure, there is math and you can somehow make some mental models involving 3d graphics and all, but that is not actually what is going on down there.

Re: Cherenkov Radiation

#36

Post by mmmattt »

Betelbuddy wrote: post #26
nuccy wrote: post #3

The title (likely intentionally) is misleading, it should say "travelling faster than light in a medium". Nothing here travels faster than light in vacuum. BTW there are special types of telescopes used to observe gamma rays - they cannot see gamma ray directly but observe a flash of Cherenkov light of a cascade of charged particles created when gamma ray hits atoms in the atmosphere. Those telescopes are Imaging Atm…

>> The title (likely intentionally) is misleading, That is because that is not the title...the title is: "What is Cherenkov Radiation?"

He obviously meant the title of the HN post? Why not straight up say that the article title is different and avoid the passive aggressiveness.

Re: Cherenkov Radiation

#37

Post by maxnoe »

The article has a section about what it can be used for, but only mentions the uses of the IAEA.

Of course I am biased because I work in the field, but the by far most wide reaching application of Cherenkov radiation is in the detection of high energy particles, particularly in astrophysics.

- Imaging Atmospheric Cherenkov telescopes detect the Cherenkov radiation emmited in the atmosphere when a high energy cosmic ray or gamma ray creates an air shower

- Water Cherenkov Detectors detect Cherenkov light when the secondary particles of these air showers reach water tanks on the ground

- Neutrino telescopes like kamiokande, Icecube and km3net detect Cherenkov radiation in water or ice produced by secondary particles produced by the rare interactions of Neutrinos in their detector volumes

Modern, high energy astrophysics is all about detecting different kinds of Cherenkov radiation and then reconstructing the original particle properties.

Re: Cherenkov Radiation

#38

Post by prathje »

spwa4 wrote: post #27
prathje wrote: post #15

It took me a long time to develop an intuition for light and electromagnetic wave propagation, and I’m still working on it. Fundamentally, changes in the EM field propagate always with the speed of light in a vacuum, i.e., c (also known as the speed of causality). Single EM waves propagate with exactly this speed and they do not magically slow down in a medium... they propagate happily at speed c! (FYI EM waves are m…

> Single EM waves propagate with exactly this speed ... Yes ... and no. Or we should say yes, but not necessarily forward. What about circular? What about ball shaped? What about a vortex? Any valid soliton is a solution and a single wave. Which means this is not just possible in water, but also in the electromagnetic field: https://www.youtube.com/watch?v=909o_kbCdFgll Circular (as in 2d circular in 3d space) propag…

Love this, good point! It really shows how difficult it is to give an easy explanation that generalizes well... So, although quite abstract, the fundamental propagation of changes in the EM field at the speed of causality is a good enough approximation?

Re: Cherenkov Radiation

#39

Post by pfdietz »

hdgvhicv wrote: post #10
chinathrow wrote: post #7

> How can something travel faster than light? > Nothing can travel faster than the speed of light in a vacuum. However, in other mediums, particles can potentially move faster than light. For instance, while in water, light would instantly slow down to 75% of its normal speed, but there are other particles that don’t slow down as much and end up moving faster than light. Whenever that happens, a blue or violet glow o…

In water photons travel at say 200,000km a second. Neutrinos travel at nearly 300,000km a second. That’s causes a blue glow. Which is how neutrino detectors work.

> In water photons travel at say 200,000km a second.

It really depends on the energy of the photons. There is "dispersion". It's the same effect that causes a prism to split white light into different wavelengths.

Re: Cherenkov Radiation

#40

Post by weinzierl »

I had learned about Cherenkov Radiation and its characteristic blue color at university. When, a couple of years later, the university had finished building a new research reactor, they had an open house day with guided tours. Of course I’d take one!

The new reactor was of the swimming pool type, and seen from the wraparound gallery above, you could easily mistake it for one. Except for the blue shimmer in the water.

Remembering my studies, my head went hot and cold. Hadn’t they said the reactor wasn’t operational yet? Or had I just assumed, because of the open day? ub So I hesitantly approached our guide and asked about the blue light, to which he answered in the most casual way you can imagine:

"Oh, that’s because of the Cherenkov Radiation."

Pause.

Laughter. Seeing the doubts in my eyes he had just been messing with me, and they had deliberately installed blue lights there to make the experience more realistic for the open day

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