Faster than the speed of light travel/ Cherenkov

tierless · Dec 14, 2004

Cherenkov radiation/ Blue Glow Cherenkov radiation (also spelled Cerenkov) is electromagnetic radiation emitted when a charged particle passes through an insulator at a speed greater than that of light in the medium. The characteristic "blue glow" of nuclear reactors is due to Cherenkov radiation. It is named for Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to rigorously characterize it. While relativity holds that the speed of light in a vacuum is a universal constant (c), the speed of light in a material may be significantly less than c. 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. Cherenkov radiation results when a charged particle, most commonly an electron, exceeds the speed of light in a dielectric medium through which it passes. Moreover, the velocity of light that must be exceeded is the phase velocity rather than the group velocity. The phase velocity can be altered dramatically by employing a periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity — a phenomenon known as the Smith-Purcell effect. In a more complex periodic medium, such as a photonic crystal, one can also obtain a variety of other anomalous Cherenkov effects, such as radiation in a backwards direction (whereas ordinary Cherenkov radiation forms an acute angle with the particle velocity). As a charged particle travels, it disrupts the local electromagnetic field in its medium. Electrons in the atoms of the medium will be displaced and polarized by the passing EM field of a charged particle. Photons are emitted as an insulator's electrons restore themselves to equilibrium after the disruption has passed. (In a conductor, the EM disruption can be restored without emitting a photon.) In normal circumstances, these photons destructively interfere with each other and no

rogers_buck · Dec 15, 2004

They failed to mention its most practical down to earh application. Earth-based high energy astronomy. Earth bound gamma ray telescopes exist in a variety of forms. The most common is the giant light bucket. The Solar Thermal Test Facility in Albaquerqi NM was first tried out as a Gamma Ray telescope by Weekes et al back in the early 80's. There were problems with the RTL based electronics and analysis methods given the extended light path. Since then the STTF has been successfully used routinely to make Gamma Ray observations in the 10^20 GeV range. Dedicated gammar ray telescopes of the light bucket design are employed at several locations including Mt. Hopkins Whipple Observatory in Arizona. The second type of earth-bound gamma ray telescope that has been tried uses light conversion panels. These are plastic panels that contain an organic dye that convert incident far blue light to a longer wavelength and use a waveguide design to bring the light to photo-multiplier tubes. The data processing involved in detecting gamma rays and distinguishing them from other phenomena including atmospheric cosmic ray showers is done using a monte-carlo analysis of data collected over many hours of observation. To my knowledge, photo-multiplier tubes are still among the best types of detectors of atmospheric cerenkov having a good match to the spectrum and short duration of this type of flash. In addition to searching for gamma ray sourcese in the night sky, the large 10 meter gamma ray telescope on Mt. Hopkins was used by Weekes, et al to search for exploding primordial black holes left over from the big bang. In this modality, the massive instrument was pointed at the side of a nearby mountain (Mt. Wrightson) to detect the interphase with the earth and the air. This work helped establish a lower limit for such events. I helped with the initial STTF experiments and spent many a blissfull hour making observations using the 1

CalliArcale · Dec 15, 2004

Thank you for that explanation! I'd never really known what Cherenkov radiation was, although I'd certainly heard it mentioned, and knew it had something to do with nuclear physics. Thanks! I learned something this morning! <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

Saiph · Dec 15, 2004

good explaination indeed. Another neat fact: The "blue room" incident during the manhattan project, where two samples of uranium (or was it plutonium) were accidentally merged during critical mass measurements (by slowly bringing them together, but not crossing the threshold) was not named because it was in a blue room. The intense radiation from the merged samples (which was above critical mass, but not much, so the reaction was fast, and growing, but not catastrophic) instead created Cherenkov radiation, suffusing the room with blue light (i.e. the air glowed blue). Pretty creepy, and lethal. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

silylene old · Dec 15, 2004

The same blue flash was observed in the 1999 Japanese nuclear accident, which killed 2. ++++++++++++++++++++++++++++++++ When and where did the accident take place? An inadvertent nuclear chain reaction, or so-called “criticality accident,” began at 10:35 AM local time on Thursday, September 30 at the JCO Co. Ltd. Conversion Test Building at Tokai-mura, Japan, about 75 miles northeast of Tokyo. The chain reaction, which gave off intense heat and radiation, could not be stopped until 18 hours later. The accident began when workers were converting enriched uranium into oxide powder for use in preparing fuel for the Joyo experimental fast breeder reactor. This reactor is part of Japan’s plutonium-production program. The uranium was enriched to 18.8% U-235, far higher than the 3 to 5% enriched uranium used as fuel in Japan’s conventional nuclear power reactors. Breeder fuel, whether enriched uranium or plutonium, is far more susceptible to criticality accidents than power-reactor fuel. What happened? It appears that workers deliberately circumvented safety measures to save time. A solution of uranyl nitrate was transferred into a large-volume precipitation tank, rather than the smaller, cylindrical container required by regulations. According to JCO Inc. official Yutaka Tatsuta, one of the injured workers reported that some 16 kilograms of uranium solution had been poured into the precipitation tank, nearly eight times more than its criticality safety limit of 2.4 kilograms. Workers reported seeing a blue flashand then started to feel ill. According to one report, “the area was wrapped in a haze of blue smoke.” Workers told plant staff that “they saw a blue flame rising from the fuel.” Kenji Sumida, a member of Japanese government’s Nuclear Safety Commission, concluded, “I know this is difficult to believe, but I think that we have no choice but t <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

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Faster than the speed of light travel/ Cherenkov

tierless

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rogers_buck

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