Naked Science Forum
General Science => General Science => Topic started by: Naufal the B. S. on 05/10/2009 13:25:58
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How to build electron gun?
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I wouldn't bother; I would just salvage one from an old television.
What do you want it for?
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Electron guns only work in near vacuum, (like in a CRT (http://en.wikipedia.org/wiki/Cathode_ray_tubes)).
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Does junk television contain junk electron gun too?
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The electron gu is not likely to be the first part to fail.
Most old TV sets (old enough to have a CRT rather than an LCD) will have a working electron gun.
However, while it would be fairly easy to get it out of the picture tube, it would be very difficult to get it to do anything interesting.
Do you have a very good vacuum pump?
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It wont be powerful enough to kill people though...
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It's not the power that stops it killing people. Its the fact that it will only work in a vacuum and there are no people in a vacuum.
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Space? Joke [:D]
so, why egun cannot works "in not vacuum"?
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Electrons are much lighter than air molecules so the air would stop them.
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How about this diagram? Does it need vacuum?
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Electron guns only work in near vacuum, (like in a CRT (http://en.wikipedia.org/wiki/Cathode_ray_tubes)).
The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen. The image may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets and others.
http://en.wikipedia.org/wiki/Cathode_ray_tubes
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How about this diagram? Does it need vacuum?
Of course it needs a vacuum.
The electrons don't know what sort of gun they have been fired from so they behave exactly the same way. When they bummp into the air they stop.
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They typically make the electron gun using a tungsten filament - which would oxidise in air in a few 10's seconds or quicker if operated at the usual dull red heat.
For use in air you could use a nichrome wire (which won't oxidise)... but as others have suggested, the mean free path of an electron in air (how far it travels before bumping into gas molecules) is something less than a millimetre.
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(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fweb.me.com%2Fawcg%2FiWeb%2FBF%2FPhotos_files%2FDeathray.jpg&hash=752d4a4d246f4b8223d99a22b556294c)
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How about this diagram? Does it need vacuum?
Yes vacuum is must for e-beam. To know more about this try to know something about Scanning Electron Microscope.
There are many reasons for requiring a vacuum in an SEM. If the filament were surrounded by air, it would quickly burn out, like a light bulb. If the column were full of air, the electrons would collide with the gas molecules.
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They typically make the electron gun using a tungsten filament - which would oxidise in air in a few 10's seconds or quicker if operated at the usual dull red heat.
Yes, and in a beautiful white 'puff', becoming yellow tungsten oxide (you won't believe me but this is the way I made this chemical [:)])For use in air you could use a nichrome wire (which won't oxidise)
At which temperature? Certainly not at the ~ 3000°C of a tungsten filament in a lamp...(it melts much before...).
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If I had money to burn I could use a yttria coated rhenium filament which would survive being heated to bright red or even white heat in air.
It would still be as much use as a chocolate teapot for an electron gun in air because, as has been said, the range of the electrons is somewhere between not a lot and nothing.
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If I had money to burn I could use a yttria coated rhenium filament which would survive being heated to bright red or even white heat in air.
This is interesting. Do you have any more information, or links about it?
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I know they use them in mass spectrometers. The advantage is that they don't die if you let some air in.
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I know they use them in mass spectrometers. The advantage is that they don't die if you let some air in.
Thank you.
What intrigues me is the fact a not-so-small layer of oxide can behave well, physically, at high temperature on a metal body: usually oxides have very different thermical and mechanical properties from metals, just to say one, thermal expansion coefficient. Obviously in this case they coexist quite well...weird.
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make a rail gun instead :)
http://science.howstuffworks.com/rail-gun.htm
But don't point it at me ::))