Question

Why does the energy of characteristic x rays become increasingly greater for heavier atoms?

a) Heavier atoms have more electrons, leading to higher energy transitions.

b) Heavier atoms have lower binding energies.

c) The energy of characteristic x rays is independent of atomic weight.

d) Heavier atoms emit fewer characteristic x rays.

Answer 1

Characteristic X-rays have higher energy in heavier atoms because they are produced when tightly bound inner-shell electrons are replaced, with the energy released increasing proportionally to the square of the atomic number (Z^2).

Step-by-step explanation:

The energy of characteristic X-rays increases for heavier atoms because inner-shell electrons in such atoms are more tightly bound due to a stronger nuclear charge, indicated by a higher atomic number (Z). When an inner-shell electron vacancy is filled, the energy released as an X-ray photon is proportional to the square of the atomic number (Z2), which means that heavier elements will emit X-rays with higher energy. Therefore, as we move to heavier elements with larger atomic numbers, the energy needed to remove an inner-shell electron increases significantly, and consequently, the energy of the characteristic X-rays emitted when these vacancies are filled also increases. In the context of X-ray tubes, higher accelerating voltages are required to knock out inner-shell electrons, especially in heavy elements such as tungsten, which is frequently used as an anode material due to its high melting point.