HV capacitors which emit x-rays?!!!

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

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.

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

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

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.

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.

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)

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

Does it date this website?

Bob Weiss N2IXK

You underestimate the internet!

Chris

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.

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.

Wrong,

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

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

Isn't there a vacuum inside TV picture tubes?

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

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

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

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

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"