During an x-ray exposure, an incident electron with 84 keV passes very close to the tungsten nucleus. What is the approximate energy of this electron as it exits the atom?

During an x-ray exposure, an incident electron with 84 keV passes very close to the tungsten nucleus. What is the approximate energy of this electron as it exits the atom?

• A. 60 keV
• B. 1 keV
• C. 84 keV
• D. >100 keV

Answer: (B)

When a fast electron approaches a heavy nucleus, the strong Coulomb field causes a rapid deceleration (acceleration) of the electron. This intense interaction produces bremsstrahlung radiation, so a large portion of the electron’s kinetic energy can be emitted as an X-ray photon. If the encounter is very close, most of that energy can go into radiation, leaving the electron with only a small residual amount of energy. For an 84 keV electron that skims the tungsten nucleus, the remaining energy after the encounter is typically around a keV. So the exiting energy is about 1 keV. This makes sense because energy cannot exceed what the electron started with, and a near-nucleus pass favors substantial energy loss through radiation, not preservation of the full 84 keV.

When a fast electron approaches a heavy nucleus, the strong Coulomb field causes a rapid deceleration (acceleration) of the electron. This intense interaction produces bremsstrahlung radiation, so a large portion of the electron’s kinetic energy can be emitted as an X-ray photon. If the encounter is very close, most of that energy can go into radiation, leaving the electron with only a small residual amount of energy. For an 84 keV electron that skims the tungsten nucleus, the remaining energy after the encounter is typically around a keV. So the exiting energy is about 1 keV. This makes sense because energy cannot exceed what the electron started with, and a near-nucleus pass favors substantial energy loss through radiation, not preservation of the full 84 keV.