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Re: glass vacume gaps x-rays

Subject: 
        Re: glass vacume gaps
  Date: 
        Sun, 13 Apr 1997 18:04:30 -0400
  From: 
        104521.363-at-compuserve-dot-com
    To: 
        "INTERNET:tesla-at-pupman-dot-com" <tesla-at-pupman-dot-com>


>Could high voltage flowing thru a vaccume create X rays?
>
>
Chris,  

It could provided that electrons were emitted in some fashion from one
of
the electrodes. (thermionic, high field emission, photoelectric, etc.) 
When
this does happen, it always occurs at the negative electrode.  The anode
or
(+) electrode material is important to the emission as well as the
actual
voltage across the tube.

Richard Hull, TCBOR

All,
X-rays are the direct result of a change in the kinetic energy of an
atom's
orbiting electrons.

In order to generate x-rays, you need to have three things,
1. A sufficiently high voltage gradient in the tube (or similar
structure)
so that the electrons are moving sufficiently fast (perhaps possible in
some very hv tesla coil designs)

2. A target which will be amenable to the generation of x-rays.  Ie, the
electrons when they strike the target must have a sufficient change in
kinetic energy so that the resulting photons will have a sufficiently
high
frequency.  By conservation of energy, if the electron's kinetic energy
drops drastically (collision), the energy must be somewhere: it goes
into
heat, light, uv and x-ray production  (one reason gaps are fair uv
generators).

3.  Enough electrons of 1 and 2 so that any x-rays will be detectable.

There are two main x-ray types: Bremsstrahlung and Characteristic.  The
first type is due to the multiple kinetic energy loss of electrons
striking
a solid/liquid/gaseous target.  As the electron burrows into the target,
it
suffers collisions with the orbiting electrons of the target's atoms. 
You
can't get around this without careful material choices.

The second type is due to the shell transitions in the target material:
tungsten, molyb, etc.  This can be controlled by simply choosing low
molecular density metals.

Usually, you need voltages on the order of 40kv dc and above in the tube
(70kv+ is much better) for x-ray production with the ususal materials
(tungsten, thorium etc).  However, you can have "soft" x-ray generation
(35-45 kv dc) a la breast mamogram machinery but the targets are usually
berillium which is expensive, toxic, hard to acquire and not used in
usual
coils.

A good reference: "Aspects of medical radialogy" by Christensen.  It
covers
x-ray production from tubes and the like.

So, to avoid x-rays, use tube voltages under 40 kv dc or make certain
you
have about 6-8+ mm of aluminum shielding around your high voltage tube
to
attenuate the possible x-rays (this is done in the medical community).

Kyle
(The usual email disclaimer)