What is the principle of taking X-rays in a hospital?

X-ray can't penetrate metal because it is strongly absorbed by metal. Bone contains a lot of calcium (a metal), which can absorb X-rays. Metals can absorb X-rays because the light wave energy of X-rays is enough to excite electrons in the inner orbit of metal ions. When electrons are excited, they absorb the light energy of X-rays and make a transition. At this time, X-rays are converted into ionization energy and remain in electrons. The light wave energy of ordinary light is much lower than that of X-rays. Electrons that cannot excite elements will be reflected back in the form of light energy and absorbed and diffused in the form of heat energy. X-ray irradiation of nonmetals will also excite electrons in their internal orbits, but the energy required for electron transition of nonmetallic elements is very low. Even if all electrons are excited, it is not enough to absorb all the energy of X-rays. Unabsorbed X-rays can pass through the non-skeletal parts of human body.