Indeed, x-rays are mostly generated by slamming high-velocity electrons into a tungsten target, x-rays are emitted as 'braking radiation' as those electrons rapidly slow down through collisions with tungsten nuclei. Old school x-ray generation resulted in some visible light photons, so there was a glow from the x-ray tubes. Being able to see the x-ray tube, of course, turned out to be a bad idea. Apropos of nothing, x-ray is the coolest name for something ever.
Cherenkov radiation is a similar-ish but not at all phenomenon that results in visible spectrum photons when particles end up travelling faster than the speed of light* in a medium (basically, when they pass one medium to another, and the phase velocity of light changes). Again, if you can see it, it's probably a really bad idea to say 'ooo, that's nice, let me get a photograph.'
Back when I used to work a 32-phosphorous, mostly a moderately high energy beta-emitter, so spits out a fast electron and an electron antineutrino, it was notable that exposed sources would attract flies. I assume that was because those electrons were causing some UV fluorescence in the acrylic shielding that the flies could see and humans couldn't. Or the flies wanted superpowers. They could have gone down the corridor, the people there were happily zapping them with full-on gamma rays.
*you can actually travel faster than the speed of light, provided that's not the speed of light in a vacuum.