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HV capacitors which emit x-rays?!!!

I stumbled across an odd idea.

If a home-built stacked-plate capacitor is operated with high-volt pulses, the thin air film trapped between the foils and the dielectric sheets should glow violet. (I verified this idea using a quickie test device made from a thin glass bowl, foil on the bottom, and salt-water on the top. Sure enough, there's a purple glow shining from the foil surface under the glass.)

Ah, but we know that plasma leads to pumping: both from ion pump effects where gas molecules embed into metal surfaces, and also from N2 turning into metal nitrides, and O2 turning into metal oxides. (Plasma does chemistry.) And there's not much air involved, so the pressure should plummet fairly fast.

So I use silicone to seal up the edges of the foil on the glass/saltwater cap, then run it for awhile. Sure enough, the purple glow changes color after a few minutes. Becomes greyish. Maybe even greenish. Might be a pressure change, or it might be contamination from the silicone caulk. I place it on the large ion chamber of a GM counter, but don't detect any rise above background count. I could keep running it for lots more minutes, but I'd burn down the contacts of my little "vacuum tester TC."

So... any Tesla coil capacitor which is sealed but which isn't vacuum-impregnated with oil is going to have plasma-filled air films, and the internal pressure is going to drop over time. And in theory, over time these air layers might pump down to non-glowing vacuum and then start emitting soft x-rays!

What to do? The whole problem might be a crackpot idea. It's all speculation (except for my glass/saltwater test.) Suggestion: paint the outside of your home-built well-sealed Tesla coil stacked-plate capacitors with ZnS glow-in-dark paint. Run them in a darkened room separate from the bright streamers and spark gap. Or instead make an xray alarm: a solar cell as sensor, painted with fluorescent paint and embedded in black epoxy or silicone.

First one to detect a dim green glow wins a prize: slightly irradiated gonads!

:)

If the effect ever proves real, then does it mean we can replace the vacuum tube in the dentist office with a bunch of aluminum foil layers with spontaneously-appearing vacuum inside? (And would a cylindrically wrapped capacitor act as a line-source of x-rays?)

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066 http//staff.washington.edu/wbeaty/

Reply to
billb
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Carry on testing. I'd suggest using a TV LOPT if you have equipment problems.

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Reply to
Sorcerer

I don't know about that, but I do remember a "science experiments" book from my high school library that suggested using a color television high voltage rectifier tube as an X-ray source.

That source (plus the fact no book would _dare_ suggest any such thing nowadays) dates the book.

Reply to
Michael Moroney

I will try to discourage you. The light you see is probably corona. You need to have high energy electrons (tens of keV's) to get any x-rays with penetrating capability. Electrons traveling in a gas, ionized or not, will just not reach sufficient energy because of collisions with air molecules. If you end up gettering the air to get a vacuum you will not get electrons except from photoemission or field emission. If you apply a voltage high enough to achieve that, you are likely to destroy your metal coatings well before you get x-rays.

A similar technique has been used for image intensification. In that case, you might get electron energy in the tens of eV's. Look up image intensifiers.

Bill

-- Fermez le Bush

Reply to
Salmon Egg

That's why those tubes have metal shielding.

When I hooked up a sheet of aluminum foil to an old TV high voltage supply, it sounded like ants were rustling across the aluminum as little blue sparks jumped off!

Double-A

Reply to
Double-A

On 26 Nov 2006 22:04:11 -0800, snipped-for-privacy@eskimo.com Gave us:

Whenever an electron beam (even a leak discharge) or plasma strikes a metal surface x-rays are emitted.

It's a rule.

Reply to
JoeBloe

On Mon, 27 Nov 2006 17:52:05 +0000 (UTC), snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) Gave us:

Bone up on the forum you invade.

Quote who you are replying to.

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Reply to
JoeBloe

Do consider the kinetic energy of free electrons. In corona in air, that's going to be only a couple to a few eV. I don't see silicone being airtight enough to improve upon that much from metal reacting with air unless you have a vacuum pump hooked up and running. Even if you do remove all oxygen and nitrogen, there will be argon - at a pressure greater than that inside most fluorescent lamps.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

Bill, there's a question involving transfer of electrical energy on sci.physics.research which might benefit from your input.

--
Dirk

http://www.onetribe.me.uk - The UK\'s only occult talk show
Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4 
http://www.resonancefm.com
Reply to
Dirk Bruere at NeoPax

Does it date this website?

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Bob Weiss N2IXK

Reply to
Bob Weiss

You underestimate the internet!

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Chris

Reply to
Chris Jones

need

I agree, X-rays will not be generated because the electons in the corona have lost most of their energy in molecular collisions with the gases present. Secondly, even if X-rays were formed, they wold be very low energy because the voltage is low by X-ray standards. At best, the photons could only be a few kV or so and would barely penetrate a piece of paper.

Reply to
Bob Eld

On Mon, 27 Nov 2006 20:05:02 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) Gave us:

The key then would be to laminate the plate segments to their insulative layer with a vacuum process during construction. Should probably bake out any water as well. THEN seal the edges of the plate layers, and one could even pull a vacuum on that assembly prior to cure.

Reply to
JoeBloe

Wrong,

harmful X-rays were well known side effect of the first color TVs in the

1950's, and also of some high voltage tubes.

Why do you think there is 30 pounds of LEAD in today's 27 inch TV tube ??

Reply to
smuggie

Isn't there a vacuum inside TV picture tubes?

Reply to
mrdarrett

And anyway it doesn't work! Well, if you find an old enough tube I guess it does. In the 1970s they switched over to lead glass in the rectifiers and in the CRT faceplate.

If we ignore the cancer danger, x-rays aren't that bad. For example, a typical dental x-ray head cannot give you an x-ray burn. It takes a year or two to get enough of a dose to give the mildest burn, and your skin will heal faster than it's damaged. It's like weak sunlight: too dim to get a sunburn.

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066

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Reply to
Bill Beaty

Definitely. But go look up "ion pump." Apparently they're common in small high-vac systems. No moving parts.

If you have metal with high enough negative voltage, slowly it will scavange up all the remaining gas as accelerated ions become embedded.

On the other hand, if the mean free path for electrons is shorter than the empty space inside the cap, then all you need is electrons and a strong enough e-field.

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066

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Reply to
Bill Beaty

Agreed.

Wrong. What do you mean by "gas?" We have to consider the issue of pressure and mean free path for electrons.

For example, the old-style Roentgen x-ray tubes would stop working if pumped down to really hard vacuum. They did not operate by field-emission alone, instead they required electrode collisions with the trace of gas ions remaining. Before GE/Coolidge introduced hot-filament x-ray tubes around the 1930s, non-filament medical x-ray tubes would include a small gas-generator (such as a piece of coal) in a glass side-arm. If the internal pressure decreased too much because of ion-pumping effect,

the coal-chunk could be warmed in order to restore the (low) pressure.

Yet the old-style Roentgen tubes worked just fine.

If we slowly reduced the electrode spacing in those old tubes, what effects would arise that could prevent proper operation?

On the other hand, the dielectric sheets exposed to plasma would spew out ions and raise the gas pressure. Even quartz would generate oxygen. So use intrinsic silicon wafers as the dielectric?

:)

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066

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Reply to
Bill Beaty

Sorry about that. I agree. The mean free path has to be long enough for the electron to gain energy between collisions. I was not thinking about that for the small gaps at relatively high pressure found in capacitors.

Residual gas can help in the formation of electron beams. The ions can neutralize space charge repulsion effects and help keep beams focused.

Bill

-- Fermez le Bush

Reply to
Salmon Egg

Sure. And the electron energy is around 25-30 keV. that's significant.

Mati Meron | "When you argue with a fool, snipped-for-privacy@cars.uchicago.edu | chances are he is doing just the same"

Reply to
mmeron

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