Production and Use of X‑rays – A‑Level Physics 9702
Production and Use of X‑rays
1. How X‑rays are produced
X‑rays are generated when high‑energy electrons are decelerated rapidly upon striking a metal target. Two
processes contribute to the emitted radiation:
Bremsstrahlung (braking radiation) – a continuous spectrum produced by the
deceleration of electrons in the electric field of the nuclei.
Characteristic radiation – discrete lines resulting from electron transitions
between inner atomic shells of the target material.
2. Typical X‑ray tube arrangement
A high voltage source accelerates electrons from a heated cathode toward an anode (usually tungsten). The
resulting X‑ray beam exits through a thin window and may be filtered or collimated before use.
Suggested diagram: Schematic of an X‑ray tube showing cathode, anode, high‑voltage supply, and beam path.
3. Uses of X‑rays
Medical imaging (radiography, CT scans)
Industrial radiography for non‑destructive testing
Crystallography and material analysis
Radiation therapy for cancer treatment
4. Attenuation of X‑rays in matter
When an X‑ray beam passes through a material of thickness $x$, its intensity $I$ is reduced according to the
exponential attenuation law:
$$
I = I_0 e^{-\mu x}
$$
$I_0$ – initial intensity (before the material)
$I$ – transmitted intensity (after the material)
$\mu$ – linear attenuation coefficient (units: $\text{m}^{-1}$)
$x$ – thickness of the material (m)
5. Factors affecting the attenuation coefficient $\mu$
Photon energy – higher energy X‑rays are less attenuated.
Atomic number $Z$ of the absorber – high‑$Z$ materials have larger $\mu$.
Density of the material – denser materials provide greater attenuation.
6. Example calculation
Determine the thickness of aluminium required to reduce a 50 ke \cdot X‑ray beam to 10 % of its original intensity.