Which is the reverse process of x-ray production?

The reverse process of x-ray production is called the photoelectric effect. In the photoelectric effect, an incident photon interacts with an electron in an atom, transferring its energy to the electron and causing the electron to be ejected from the atom. The minimum energy required for this process to occur is called the ionization energy of the atom. The kinetic energy of the ejected electron is equal to the difference between the energy of the incident photon and the ionization energy of the atom.