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

Photoelectric Absorption
An atom completely absorbs a photon, which then disappears; this excess
energy provided to the atom ultimately results in ejection of an orbital electron.
The ejected electron is known as a photo electron.
Electrons have binding energies of orbit, with outer shells having less energy
than those closer to the positive nucleus. When the initial orbital vacated is
not that of an outer valance electron, the atom remains in a high-energy state
until an outer orbital electron shifts to fill its incomplete inner shell. This shift is
accompanied by emission of a characteristic X-ray.
Photoelectric Absorption is an important interaction for low energy photons
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