Which interaction produces discrete spectral lines in the x-ray spectrum?

• A. Bremsstrahlung
• B. Photoelectric
• C. Characteristic
• D. Compton

Answer: (C)

Discrete lines in the x-ray spectrum come from electrons transitioning between bound energy levels in the target atoms after an inner-shell vacancy is created. When an inner-shell hole (like in the K-shell) is filled by an electron from a higher level, the energy difference between those shells is emitted as a photon. Because those energy differences are fixed for a given element, the emitted photons appear at specific energies, producing sharp lines known as characteristic radiation (examples include K-alpha and K-beta lines).

Bremsstrahlung, by contrast, results from the continuous deceleration of fast electrons in the atomic field, yielding a continuous spectrum of photon energies. The photoelectric effect involves absorbing a photon and ejecting an electron, not emitting discrete lines. Compton scattering produces photons with a range of energies depending on the scattering angle, also a continuum.