Thanks
When the bulb is "struck" a high voltage RF pulse is feed to the bulb. Because the RF voltage is an alternating current, both electrodes are being hurt. The ignition voltage is high enough to ionize the gas between the electrodes, and an arc forms between the gaps. Because the gap has already been broken down, the low voltage DC can cross the gap, and produce lots of light.
Any other questions
Josh
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"Film is made of silver, video is made of rust"
'nuf said
The anode is the positive electrode of the lamp. (The cathode is the negative.) Electrons come in through the anode and jump the gap toward the other electrode. The xenon gas gets excited and gives off light. It's kind of like a subatomic game of billiards.
Xenon is one of the noble gases. (Helium, Neon, Argon, Krypton and Xenon.) They are VERY stable atoms. They have all of their elecrons in their outer shell. (Think like the solar system... The sun is the nucleus and the planets are the electrons.) Since it's very hard to knock an electron out of place in an atom like that, noble gases don't react with other elements very easily.
So, here comes this electron jumping off the the cathode and "flying" though an atmosphere of xenon gas. A lot of those electons are bound to hit an atom of the gas. When it does, one of the electrons in the outer shell gets knocked away from it's "ground state" into a larger orbit. The electron doesn't like that and wants to go back to the way it was. When it snaps back to it's original place it gives off the extra energy in the form of a photon.
Now, imagine that a huge number of electrons (6.25 X 10^25) TIMES the number of amps your lamp burns at) jumping that gap every second. Put a like number of xenon molecules inside that glass envelope (hence, the reason there is so much pressure inside) and think about the number of little collisions there would be... and how many photons would be given off. We're talking GOZILLIONS!
The anode is just the "landing pad" for those electrons after they have made the jump. The reason it's larger than the other one is that they need a bigger target. After being bounced off a few zillion xenon atoms they aren't flying in a straight line anymore so they become spread out. Sort of like the way water comes out of a garden hose when you put it on fine spray.
The anode (and the cathode) are made of tungsten alloy because they need to be able to withstand the heat caused by the hundreds of culoumbs of electrons whizzing through them every second. Even then, they can't withstand that kind of tourture forever. Ever notice that the ends of the electrodes get rounded off after they have been used for a while? That's because some of the metal has been literally vaporized. When the glass in your xenon lamp starts getting dark grey or black, that's becasue the metal vaporized off the elecrodes has deposited itself there.
When enough of the metal has been eroded it's time to replace the lamp. Otherwise the blackening will block a lot of the light. I would bet that it would cause the glass to get hotter too and raise the chances that the glass will fail. When the electrodes get worn away they start operating inefficiently. It takes more and more energy to push them across the gap. The heat goes up and less and less light gets produced. Finally, the lamp will give out all together if you don't replace it. It it gets too bad, the glass will give way or else the ceramic seal on the end of the lamp will blow out.
When that happens, the gas inside there will get really big... really fast! (It will explode.) If you're lucky it will just go, "Ffffsssshhhhhhh!" and leak out in a semi-controled manner. Then the air will get in and start burning. That's what causes the inside of a lamp to go milky white, sometimes, when they fail.
or "POW!"
Sorry, I could not resist. 
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Jan Hackett
Theater Operations Manager
Extreme Screen Dynatheater
NM Museum of Natural History Foundation
I don't think so. If that were true, xenon bulbs would require extensive labeling re: the radioactive materials, and used bulbs would be considered HAZMAT and require specialized (read expensive) disposal .
-Aaron
JJ
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"Film is made of silver, video is made of rust"
'nuf said
Electrons enter through the negatively charged CATHODE and jump the gap to the positively charged ANODE. Those little buggers have a negative charge and they want to get to that positive charge. It's a common misconception that a current flows from the + to the -, an idea that actually goes back to Ben Franklin. The actual flow is from - to +. Otherwise, the beam in a picture tube would flow from the faceplate back into the electron gun!
Isn't it only perception anyway? Electrons do their stuff and we just need a way to visualize them doing it.
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Jan Hackett
Theater Operations Manager
Extreme Screen Dynatheater
NM Museum of Natural History Foundation
Disposal of a spent Xenon Lamp normally should not cause too much of a problem. However, I know of a person who saved up a whole bunch of cathodes. When he pointed a Geiger Counter in it's direction and had it about a foot away from the pile of cathodes, it drove the Geiger Counter nuts!
In eny avent, I would not recommend the cathodes be carried around in your pocket.
I know this shit... Honest!
Just don't ever ask me to do something like, "Go to Maple Drive, turn right and stop at house number 1321"because I'll turn LEFT on Apple Drive and stop at house number 1231!
(Paul: After they go "Pbpthbpthbthp!" the projector goes "Wooga-Wooga!" )
About 10 minutes into the reel, a strange noise was emitted from that old Super that sounded like "WOOGA WOOGA! - CLINK - BLAM..CLUNK!" Then I heard the "WOOGA WOOGA" noise on the floor, followed by a "Plop!"
By the way, are you going to put "Pbpthbpthpthp" in your dictionary? When you finish your dictionary, can I get a copy?
Would anyone be interested in doing a similar thing with discarded xenon bulb anodes and donating the proceeds to the Rick Long Memorial Beer Fund?
As for its radioactivity, the half-life of thorium (the time it would take for 1/2 half of it to radioactively decay away into something else) is extremely long, hence the radioactivity is very low. A brick house will give off a lot more radioactivity (in total) than one of those mantles from the trace amounts of uranium in the originating material (i.e., clay).
An old watch with radium dials gives off a tremendous amount of radiation, by comparison. And radium mixed with beryllium gives off neutrons, which when slowed down (by water or paraffin) will interact with other elements (like thorium) and make them radioactive through their atoms being split. That's what that kid did, in essence.
End of physics lesson -- quiz tomorrow
Mantle lamps--where gas is is burned efficiently to make heat, not illumination and the incandescent mantle creates the light--are much more efficient than traditional gaslights, with their sooty yellow flames. But did they exist in the gaslight era? If not then what are people trying to prove with gas mantle lamps out in the front yard? Can't be nostalgic if it didn't exist in olden times!
"Thorium dioxide is also much more resistant to chemical interactions, which is demonstrated by its uses as a high temperature crucible (container) or in the gas mantle (used in "Coleman" camping laterns) invented in 1885 by Welsbach; which is a fabric soaked with a mixture of thorium nitrate and cerium nitrate, which upon ignition becomes a 99% Thoria "mantle" that glows white-hot when heated by a gas flame."
http://www.easylivingsystems.com/gas-litemantles.htm
"Dr. Carl Auer von Welsbach was an Austrian chemist and engineer who invented the gas mantle,
thus allowing the greatly increased output of light by gas lamps.
In 1885 Welsbach discovered and isolated the elements neodymium and praseodymium from a mixture called didymium,
which was previously considered an element. His interest in rare-earth elements continued,
and he found that a fabric impregnated with a mixture of thorium nitrate and cerium nitrate
could be made into a mantle that glowed brightly when heated by a gas flame.
Patented in 1885, the Welsbach mantle greatly improved gas lighting and,
although largely supplanted by the incandescent lamp, is still widely used in kerosene and other lanterns.
In 1898 Welsbach introduced the first metallic filament for incandescent lamps.
Although the osmium he used was too rare for general use, his improvement paved the way for the tungsten filament
and the modern light bulb. Welsbach also developed misch metal,
a mixture of cerium and other rare earths, which he combined with iron to make Auer's metal,
the first improvement over flint and steel for making sparks since ancient times.
It is used in cigarette lighters and in strikers for lighting gas jets. "
http://www.rottnest.freeserve.co.uk/links.htm
Unfortunately, even gas illumination has environmental implications:
http://www.epa.gov/region02/superfund/npl/0203580c.htm
http://www.epa.gov/superfund/sites/rodsites/0203580.htm
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
(sorry, fairly long...)
The do-it- yourself reactor
David Hahn wanted to be an Eagle Scout, but he was not interested in typical merit-badge projects. Instead of astronomy, backpacking, or business, Hahn was interested in producing energy. He set out to build his very own breeder reactor in his mother's potting shed.
Hahn never built anything resembling a working reactor. But his merit-badge project got some attention. On June 25, 1995 agents from the Environmental Protection Agency (EPA) raided his home in the quiet Detroit suburb of Golf Manor. The extremely high levels of radioactivity the EPA found in his backyard shed prompted the agency to declare it a federal Superfund site.
Hahn was remarkably resourceful in his search for radioactive substances. According to Ken Silverstein ("The Radioactive Boy Scout," Harper's Magazine, November 1998), Hahn "figured out a way to dupe officials at the Nuclear Regulatory Commission [NRC into providing him with crucial information he needed in his attempt to build a breeder reactor, and then he obtained and purified radioactive elements such as radium and thorium."
Even at age 15, Hahn knew how to ask nrc officials for information about how to isolate radioactive elements, which isotopes were capable of sustaining a chain reaction, and where he could find commercial sources of radioactive materials. "The nrc gave me all the information I needed," he told Silverstein. "All I had to do was go out and get the materials."
Not that he had to look very far for most of his "reactor" elements. In an interview on cbs This Morning (October 19, 1998), Hahn listed his sources: "I found lantern mantels, which contain thorium dioxide. They sold these at Kmarts. . . . [I got] tritium from bow-and-arrow sights, polonium from electrostatic film brushes, americium from smoke detectors, radium from, of course, radium dials."
But, writes Silverstein, what Hahn really wanted was uranium 235, because it would provide the "biggest reaction." His first approach was to drive hundreds of miles through northern Michigan with a Geiger counter on his dashboard. The search yielded only a few rocks of pitchblende (which contains minuscule amounts of uranium 235), so he decided to go back to his friends at the nrc for help. His contacts at the regulatory commission gave him the address of a Czechoslovakian firm that sells uranium to commercial buyers. That contact resulted in a few more samples of pitchblende. His attempts to isolate and purify the uranium, however, resulted in little more than a small pile of black powder.
Armed with his radioactive cocktail末and a sketch of a checkerboard breeder reactor from one of his father's college textbooks末 Hahn began devising his backyard breeder. He knew that it took at least 30 pounds of enriched uranium末vastly beyond anything he had末to initiate a chain reaction, but he thought he could at least generate some interesting results. "No matter what happened," he told Silverstein, "there would be something changing into something末some kind of reaction going on there."
His makeshift reactor had a "core" of radium, americium, and beryllium that was wrapped in a "blanket" of thorium ash and uranium powder. And it produced. "The level of radiation after a few weeks was far greater than it was at assembly," he recounted. "I know I transformed some radioactive materials."
When his Geiger counter began picking up radiation several doors down from his house, Hahn decided that he had "too much radioactive stuff in one place," and he disassembled the "reactor." By the time the EPA showed up, he had hidden most of the radioactive materials, including the purified thorium pellets, leaving only the radium and americium behind. "The funny thing is," he joked to Silverstein, "they only got the garbage, and the garbage got all the good stuff."
The "garbage" was enough to scare the EPA, which spent $60,000 on the Golf Manor Superfund clean-up. And, according to CBS This Morning, the agency "never sent a bill."
末Michael Flynn