Increasing HVL leads to an increase in which property of the beam?

• A. beam hardness
• B. beam divergence
• C. beam angle
• D. beam frequency

Answer: (A)

Increasing HVL means the beam has greater penetrating power, i.e., it becomes harder. HVL is the thickness of material needed to reduce the beam’s intensity by half; a larger HVL indicates that more energy is required to attenuate the beam, which happens when the photons in the beam are on average more energetic. In diagnostic X-ray beams, increasing filtration or energy shifts the spectrum toward higher energies, so the beam’s quality (hardness) increases. Divergence and angle are determined mainly by the geometry and collimation of the setup, not by HVL. The photon energy distribution (frequency) is related to the beam’s energy spectrum, but the standard way we describe the effect of higher HVL is that the beam becomes harder.