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Re: spark gap x-rays !



Tesla List wrote:

> Original Poster: Hollmike-at-aol-dot-com
>
> Richard,
>      It sounds like you have the RF feedback into the mains suppressed, so I
> am thinking that the interference is due to radiation from your coil.  One
> thing you might try is to place your spark gap inside a grounded metal
sheild.
> This may at least help you determine whether or not the gap is the culprit.
> An EE buddy of mine keeps insisting that I place my gap in such a shield to
> prevent the emanation of x-rays (and VHF/UHF radiation perhaps) from the gap
> itself.

> Mike

 Although this post won't contribute to the RFI discussion, I feel that the
momentary diversion is warranted.

For those who are trying to decide if x-ray shielding is necessary on their
spark
gap, let's for a moment revisit X-R Gen physics.

1. x-rays occur as a 1% side effect of high kv anode bombardment
     (bremstraulung radiation)

2. The energy (and penetrance) of the photons generated are polyspectral
(broad
band)
     The brilliant plasma discharge of the gap goes all the way up from
infrared
to
     visible to soft and hard UV  into soft x-ray.

3. The maximum photon emitted will be proportional to the kV across the
gap, with
a
     poisson type of distribution of frequencies peaking somewhat below the
Fmax.

4. The flux of x-ray photons is current dependent. A physical chemistry
description
     Phi = P(b.r.-at-V) * I
     in which the number of einsteins of x-ray photons produced is
proportional
to the
     product of the probability of brem rad at a given e-'s kV and the
number of
moles
     of e-  impinging on the target.

Actually calculating the anticipated production of x-rays of various
frequencies
for a gaussian distribution of e- in a spark gap would implode most
calculators
and pc's, not to mention what it would do to your social life. Anyway it's
pretty
much an academic exercise. For kV's below 20, even a plywood box would be
pretty
good shielding. Aluminum would be pretty good ( a few mm would be plenty)  If
you're dealing with higher kV's than that, I would try something heavier like
1/4" steel up to 40-50 kV. Beyond that, think lead (got any old car batteries
laying around?). If you've got even temporary access to some kind of counter,
(Geiger etc.) you'd be surprised by what you'll be producing. The ultimate
shielding is of course distance. Remember, intensity drops as the square of
distance . . . stay away from the spark gap when it's running; even with
shielding.

Bryan Kaufman