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Step 18: Assemble the Radiating Head

Atmospheric air has a dielectric strength of 1.1 million volts per meter despite what Wikipedia argues. This translates to 11kV per centimeter, or 6kV with pointed electrodes. Since reliably insulating 75kV using air would require a distance larger than 10cm,
making an x-ray device compact is near impossible.

That is of course, if one does not use insulating oil!

Most oils have a dielectric strength 4 times that of air, and eliminate the corona losses which would otherwise occur in an open air design. This reason, coupled with increased thermal conductivity is the reason why nearly all x-ray machines insulate all of their high voltage components with oil, and why both mine and yours should follow suit.

A junction box does a fine job of housing the EHT components. [Image 1] displays the junction box which houses my machine's Coolidge tube, its lead shield, the voltage multiplier and a 1.8 billion ohm resistor to measure the anode voltage. A 90kV this resistor will leak the 50uA needed to fully deflect a galvanometer.

The thickness of the box’s wall will attenuate the x-rays somewhat so there likely won’t be any low energy rays escaping.  Depending on what you want to do this may or may not be a problem, but, x-rays with energies higher than 30keV should still be able to penetrate that thick plastic.
 
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