I think once you start getting potentials over 10 kV, the Schottky effect starts to give minor x-ray emissions. The more major or typical source is from tubes.

I think once you start getting potentials over 10 kV, the Schottky effect starts to give minor x-ray emissions. The more major or typical source is from tubes. Most tubes at high voltages will emit x-rays, even if that is not their intent, from an emitted electron striking the anode. This is why CRT TVs usually used thick leaded glass, to block the x-ray emissions.