X-rays have the same wave length as 2 electrones or the so called neutrino. They can visualise only subjects which have different wave length of the outer electron shell, because they hit with their electrones which have half of their length. If the object has free electrones it changes the direction of X-rays . If it has no free electrons such in gasses and fluids because their electrons are connected in neutrinos X-rays pass parallelly to them. So we may conclude that x-rays are neutrinos. They can visualise only metals because metals have free electrons. Neutrinos can hit each other and change their direction only if they are with different directions. So fluids and gases are also not absolute transparent for X-rays but metals absorb them in much bigger amounts, because electrones have the half wave length of the neutrinos.