Characteristic X-ray energies depend on

• A. Atmospheric pressure
• B. Sample mass
• C. Ambient temperature
• D. Atomic number and electron structure

Answer: (D)

Characteristic X-ray energies come from the electronic transitions that occur when an inner-shell vacancy is filled inside an atom. The energy of the emitted photon equals the difference between the binding energies of the shells involved in the transition. Those binding energies, and thus the photon energies, are set by the atom’s nuclear charge (the atomic number) and the detailed electron arrangement (electron structure). That’s why each element produces X-ray lines at specific, element-unique energies.

In practice, this is how XRF identifies elements: by measuring the energies of the characteristic X-rays and matching them to known lines. Factors like atmospheric pressure, sample mass, or ambient temperature don’t determine these energies; they may affect how many photons you detect or the peak shape and intensity, but not the photon energies themselves.