X-rays and visible light are the same thing. Both are photons, differing only in energy, and everything that separates them follows from that one difference.
Why X-rays penetrate
Visible light photons pass through air easily, which is why a room is lit. They do not pass through a hand, which is why a hand held in front of a lamp casts a shadow. The photons are absorbed or scattered at the surface and go no further.
X-ray photons carry considerably more energy, which gives them a much higher probability of passing through dense material rather than being stopped by it. Enough of them make it through a hand to reach a detector on the other side, and the variation in how many get through different parts of the hand is the image.
Nothing about X-ray imaging is exotic. It is a shadow, cast by light energetic enough to make the shadow partially transparent.
Why you cannot see them
The visible spectrum is a narrow band, bounded by infrared at the low-energy end and ultraviolet at the high-energy end. Human vision evolved to work within it and does not respond to anything outside it.
X-rays sit far beyond the ultraviolet boundary, well outside the range any biological eye detects. There is no version of looking harder that helps.
So seeing an X-ray requires converting it into something the eye does respond to.
How X-rays are made visible
That conversion is what a fluorescent screen does, and it is the oldest technique in the field.
Early systems, including the shoe-fitting fluoroscopes in the Creative Electron museum, used a screen coated with a fluorescent material such as gadolinium oxysulfide, commonly abbreviated GADOX. When an X-ray photon strikes it, the material absorbs that energy, and as the excited atoms return to their normal state they release the energy as photons in the visible range.
One X-ray photon in, visible light out. The screen glows in a pattern matching the X-rays reaching it, and the person looking at it sees the image indirectly.
Modern detectors work on exactly the same principle. A scintillator layer, often cesium iodide rather than GADOX, converts X-rays into visible light, and a silicon sensor underneath detects that light. The materials improved and the eye was replaced by a photodiode array, but the fundamental trick has not changed in over a century.
Can you touch one?
No. A photon has no rest mass, and there is nothing there to make contact with. X-rays pass through a hand without producing any sensation at all, at any intensity encountered in normal circumstances.
The complication is that this remains true well past the point where the radiation is doing damage. At extreme exposure levels, the kind associated with events like Chernobyl and Fukushima rather than with any inspection equipment, radiation causes serious biological harm. But the harm comes from ionization damaging tissue at a cellular level, and it announces itself afterward rather than at the moment of exposure.
So there is no sensation to warn anyone. Radiation is not hot, not sharp, and not detectable by any human sense.
Why that matters more than it sounds
The inability to feel radiation is the reason the entire safety apparatus around it exists.
Every other industrial hazard offers some warning. Heat is felt, noise is heard, sharp edges are seen. Radiation offers nothing, which is why safety depends entirely on shielding that contains it, interlocks that prevent exposure, and instruments that measure what the body cannot.
A dose rate meter is not a convenience. It is a substitute for a sense humans do not have.
The verdict
Can you see an X-ray? Indirectly, yes, once a fluorescent material converts it into visible light. That conversion is the basis of every X-ray image ever produced.
Can you touch one? No, and it cannot touch you in any way you would notice. In sufficient quantity it can certainly affect you, which is precisely why the equipment is built the way it is.
