Which interaction describes an x-ray photon interacting with an outer-shell electron weakly bound to the absorbing medium?

Which interaction describes an x-ray photon interacting with an outer-shell electron weakly bound to the absorbing medium?

• A. Compton scattering
• B. Coherent scattering
• C. Pair production
• D. Photoelectric effect

Answer: (A)

When an x-ray photon meets a loosely bound outer-shell electron, it tends to scatter inelastically off that electron, transferring some of its energy to the electron and coming away with less energy and a changed direction. This process is Compton scattering. The key is that the electron is only weakly bound, so it behaves almost like a free electron during the interaction, allowing the photon to lose energy and change trajectory while ejecting a recoil electron. Coherent (Rayleigh) scattering would leave the photon energy basically unchanged and involves the entire atom, not a weakly bound outer electron. Pair production needs photon energy well above the MeV range and also occurs in the atomic field but not by interacting with a single loosely bound outer-shell electron. The photoelectric effect involves absorption of the photon and ejection of an electron (usually from inner shells at diagnostic energies), which is not described by scattering off a weakly bound outer-shell electron.

When an x-ray photon meets a loosely bound outer-shell electron, it tends to scatter inelastically off that electron, transferring some of its energy to the electron and coming away with less energy and a changed direction. This process is Compton scattering. The key is that the electron is only weakly bound, so it behaves almost like a free electron during the interaction, allowing the photon to lose energy and change trajectory while ejecting a recoil electron.

Coherent (Rayleigh) scattering would leave the photon energy basically unchanged and involves the entire atom, not a weakly bound outer electron. Pair production needs photon energy well above the MeV range and also occurs in the atomic field but not by interacting with a single loosely bound outer-shell electron. The photoelectric effect involves absorption of the photon and ejection of an electron (usually from inner shells at diagnostic energies), which is not described by scattering off a weakly bound outer-shell electron.