Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

If during the ionization process, only part of the photons energy is needed to
liberate the electron, the rest of the energy is transferred to the electron in the
form of speed (velocity). Now that all of the photon's energy is accounted for,
the photon ceases to exist and total absorption has occurred. Remember that
a photon is not a particle, but acts like one. When the energy of the photon is
used, there is nothing left to cause further ionization.
Keep in mind that electrons orbit in various shells of the atom and not all
electrons have the same binding energy. This binding energy is dependent
upon the elements (Z) number and the position of the electron in the atom.
Those electrons nearer the nucleus possess greater binding energy and will
require greater photon energy to remove them than will electrons in the outer
shells.
Charlie Chong/ Fion Zhang
https://www.nde-ed.org/EducationResources/HighSchool/Radiography/photoelectric_popup.htm