Exactly, indeed. One of the links I gave shows how to use a 6BK4B rectifier tube for the purpose. No special X-ray tube or glasswork required. Most of the high voltage parts can be scavenged from old color tvs or monitors. Remember, though, only bad things will happen and the inside of a color tv is not a place of honor, no great deed is commemorated there, nothing of value is stored there...

Edit: that might sound tongue-in-cheek but please take it as hahah, only serious. You can hurt yourself with these things, you probably don't have a good reason to be experimenting with them, and if you do need to learn how to work with high voltage or ionizing radiation safely, this is not the place and I am not teaching you.