Cherenkov radiation
Discussion
This came up on another thread. Cherenkov radiation is IMHO one of the coolest things in physics.
http://en.wikipedia.org/wiki/Cherenkov_radiation
Sadly I think few people have to chance to see it first hand - I remember it being one of the most amazing things I've seen
http://en.wikipedia.org/wiki/Cherenkov_radiation
Sadly I think few people have to chance to see it first hand - I remember it being one of the most amazing things I've seen
rhinochopig said:
Only in a bag-less as they're clear plastic so can let the light in.
Me not follow! 
I understood that Cherenkov effect was due to some particles being able to travel faster than light was able to in certain substances!
In a vacuum, light (theoretically) will always travel the fastest and is one of the universal constants (currently under review elsewhere!)
Ali G said:
rhinochopig said:
Only in a bag-less as they're clear plastic so can let the light in.
Me not follow! I understood that Cherenkov effect was due to some particles being able to travel faster than light was able to in certain substances!
In a vacuum, light (theoretically) will always travel the fastest and is one of the universal constants (currently under review elsewhere!)
Cherenkov is as you describe = particles dumping energy as they pass through a medium at FTL for that medium (water in the case of core ponds / reactors)
Or is it http://www.sheldrake.org/experiments/constants/
rhinochopig said:
Oops, I misread your post.
Cherenkov is as you describe = particles dumping energy as they pass through a medium at FTL for that medium (water in the case of core ponds / reactors)
Or is it http://www.sheldrake.org/experiments/constants/
I've always thought of it as an EMR equivalent to a sonic 'boom' when particles travel faster than EMR can keep up!Cherenkov is as you describe = particles dumping energy as they pass through a medium at FTL for that medium (water in the case of core ponds / reactors)
Or is it http://www.sheldrake.org/experiments/constants/
The human retina produces an illusion of intense but transparent blue color in the air when a burst of free Neutrons speeding through the air, passes through the body (head).
This effect was described after a serious accident occurred at the Manhattan Project Laboratory in Los Alamos, New Mexico (USA) in about 1946. Canadian Physicist Louis Slotin erred in performing his work, which involved inducing and measuring small but highly energetic fission reactions. The "mistake" produced a burst of hard radiation in the room, primarily free neutrons, to which all the observing members of the team present, were exposed. All described a strange phenomenon in which they perceived that the air in the room had turned a blue color. The following excerpt explains concisely:
On May 21, 1946, with seven other colleagues watching, Slotin performed an experiment that involved the creation of one of the first steps of a fission reaction by placing two half-spheres of beryllium (a neutron reflector) around a plutonium core. The experiment used the same 6.2-kilogram (13.7 lb) plutonium core that had irradiated Harry K. Daghlian, Jr., later called the "Demon core" for its role in the two accidents. Slotin grasped the upper beryllium hemisphere with his left hand through a thumb hole at the top while he maintained the separation of the half-spheres using the blade of a screwdriver with his right hand, having removed the shims normally used.[2] Using a screwdriver was not a normal part of the experimental protocol.
At 3:20 p.m., the screwdriver slipped and the upper beryllium hemisphere fell, causing a "prompt critical" reaction and a burst of hard radiation.[9] At the time, the scientists in the room observed the "blue glow" of air ionization[citation needed] and felt a "heat wave". In addition, Slotin experienced a sour taste in his mouth and an intense burning sensation in his left hand.[2] Slotin instinctively jerked his left hand upward, lifting the upper beryllium hemisphere and dropping it to the floor, ending the reaction. However, he had already been exposed to a lethal dose (around 2100 rems, or 21 Sv) of neutron and gamma radiation.[14] Slotin's radiation dose was about four times the lethal dose, equivalent to the amount that he would have been exposed to by being 1500 m (4800 ft) away from the detonation of an atomic bomb.[15]
The website below contains a most interesting chronology of the accident.
http://web.ncf.ca/lavitt/louisslotin/beaver.html
I personally am not sufficiently technically competent to remark on whether the "blue glow" experienced is truly Cherenkov radiation in effect. impish
This effect was described after a serious accident occurred at the Manhattan Project Laboratory in Los Alamos, New Mexico (USA) in about 1946. Canadian Physicist Louis Slotin erred in performing his work, which involved inducing and measuring small but highly energetic fission reactions. The "mistake" produced a burst of hard radiation in the room, primarily free neutrons, to which all the observing members of the team present, were exposed. All described a strange phenomenon in which they perceived that the air in the room had turned a blue color. The following excerpt explains concisely:
On May 21, 1946, with seven other colleagues watching, Slotin performed an experiment that involved the creation of one of the first steps of a fission reaction by placing two half-spheres of beryllium (a neutron reflector) around a plutonium core. The experiment used the same 6.2-kilogram (13.7 lb) plutonium core that had irradiated Harry K. Daghlian, Jr., later called the "Demon core" for its role in the two accidents. Slotin grasped the upper beryllium hemisphere with his left hand through a thumb hole at the top while he maintained the separation of the half-spheres using the blade of a screwdriver with his right hand, having removed the shims normally used.[2] Using a screwdriver was not a normal part of the experimental protocol.
At 3:20 p.m., the screwdriver slipped and the upper beryllium hemisphere fell, causing a "prompt critical" reaction and a burst of hard radiation.[9] At the time, the scientists in the room observed the "blue glow" of air ionization[citation needed] and felt a "heat wave". In addition, Slotin experienced a sour taste in his mouth and an intense burning sensation in his left hand.[2] Slotin instinctively jerked his left hand upward, lifting the upper beryllium hemisphere and dropping it to the floor, ending the reaction. However, he had already been exposed to a lethal dose (around 2100 rems, or 21 Sv) of neutron and gamma radiation.[14] Slotin's radiation dose was about four times the lethal dose, equivalent to the amount that he would have been exposed to by being 1500 m (4800 ft) away from the detonation of an atomic bomb.[15]
The website below contains a most interesting chronology of the accident.
http://web.ncf.ca/lavitt/louisslotin/beaver.html
I personally am not sufficiently technically competent to remark on whether the "blue glow" experienced is truly Cherenkov radiation in effect. impish
I suspect the question could be resolved by determining which isotopes of either nitrogen or oxygen (or both, or even other, lesser-present elements, such as neon, argon, etc.) are likely to capture a neutron, thereby becoming unstable, the resolution of which may be the ejection of a photon in the visible blue range of wavelength.
Since blue seems to predominate, that might narrow the search. Other isotopes are likely also created, perhaps ejecting non-visible photons.
Surely, a curious way to be rid of loose, high-speed, and dangerous, neutrons!
impish
Since blue seems to predominate, that might narrow the search. Other isotopes are likely also created, perhaps ejecting non-visible photons.
Surely, a curious way to be rid of loose, high-speed, and dangerous, neutrons!
impish
impish said:
I suspect the question could be resolved by determining which isotopes of either nitrogen or oxygen (or both, or even other, lesser-present elements, such as neon, argon, etc.) are likely to capture a neutron, thereby becoming unstable, the resolution of which may be the ejection of a photon in the visible blue range of wavelength.
Since blue seems to predominate, that might narrow the search. Other isotopes are likely also created, perhaps ejecting non-visible photons.
Surely, a curious way to be rid of loose, high-speed, and dangerous, neutrons!
impish
I think you're missing the proposed mechanism; it's not neutron capture related, although you will certainly get some of that. It's recombination of ions followed by de-excitation just like in a plasma globe.Since blue seems to predominate, that might narrow the search. Other isotopes are likely also created, perhaps ejecting non-visible photons.
Surely, a curious way to be rid of loose, high-speed, and dangerous, neutrons!
impish
And just to clear up some babbaness that crept into the thread - light travels the same speed everywhere, it just propogates more slowly in denser materials. Photons travel at exactly C at all times and in all mediums. If a bloke runs across a 100m field at 10m/s he'll take 10 seconds to get from one side to the other. Put a few obstacles in his way and he'll still run at 10m/s but might take 20 seconds to get from one side to the other because he's dodging s
t. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).
t. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).carmonk said:
And just to clear up some babbaness that crept into the thread - light travels the same speed everywhere, it just propogates more slowly in denser materials. Photons travel at exactly C at all times and in all mediums. If a bloke runs across a 100m field at 10m/s he'll take 10 seconds to get from one side to the other. Put a few obstacles in his way and he'll still run at 10m/s but might take 20 seconds to get from one side to the other because he's dodging st. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).
In some media the particle emitting ER can travel faster than the radiation emitted - hence Cherenkov.t. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).Wave/particle duality of EM suggests that photons and the 'waves' are inseperable - so not sure why you suggest photons travel at C at all times in all media?
Ali G said:
carmonk said:
And just to clear up some babbaness that crept into the thread - light travels the same speed everywhere, it just propogates more slowly in denser materials. Photons travel at exactly C at all times and in all mediums. If a bloke runs across a 100m field at 10m/s he'll take 10 seconds to get from one side to the other. Put a few obstacles in his way and he'll still run at 10m/s but might take 20 seconds to get from one side to the other because he's dodging st. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).
In some media the particle emitting ER can travel faster than the radiation emitted - hence Cherenkov.t. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).Wave/particle duality of EM suggests that photons and the 'waves' are inseperable - so not sure why you suggest photons travel at C at all times in all media?
Ali G said:
carmonk said:
And just to clear up some babbaness that crept into the thread - light travels the same speed everywhere, it just propogates more slowly in denser materials. Photons travel at exactly C at all times and in all mediums. If a bloke runs across a 100m field at 10m/s he'll take 10 seconds to get from one side to the other. Put a few obstacles in his way and he'll still run at 10m/s but might take 20 seconds to get from one side to the other because he's dodging st. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).
In some media the particle emitting ER can travel faster than the radiation emitted - hence Cherenkov.t. His speed doesn't change, his path does, and that's why light appears to travel slowly, but doesn't. (with light it's not the same photon that emerges but still, the analogy sort of works).Ali G said:
Wave/particle duality of EM suggests that photons and the 'waves' are inseperable - so not sure why you suggest photons travel at C at all times in all media?
Because they do. I think you're confusing group velocity with another velocity, the name of which I can't think of right now (edit: phase, just looked it up), but which describes the speed of the wave peak which is not an actual photon and carries no information.R300will said:
isn't wave/particle duality more to do with electrons?
Not really - light (and all electromagnetic radiation) seems to exhibit both wavelike and particle like behaviour. Photons are the 'particle' incarnation of EMR.For instance - light will defract like normal waves do, but will also appear to be a lump or particle of energy when interacting (hitting) a molecule of CO2
for example.Gassing Station | Science! | Top of Page | What's New | My Stuff