American Society of Radiologic Technologist (ASRT) Practice Exam

The kinetic energy deposited per unit mass of air from an x-ray beam is measured by:

1. Absorbed dose.

2. Equivalent dose.

3. Air kerma.

4. Exposure.

The correct answer is: Air kerma.

The correct choice is focused on air kerma, which specifically measures the kinetic energy transferred to air from an x-ray beam per unit mass. This concept is critical in the context of radiation dosimetry, as air kerma provides an indication of the amount of energy that ionizing radiation imparts onto a specific mass of air, which can be directly related to the radiation exposure experienced by patients and personnel. Air kerma is expressed in grays (Gy) and is important for characterizing the radiation fields in diagnostic imaging and radiation therapy. It signifies the energy available to create ion pairs in air, which, in turn, helps to assess the potential biological effects of the radiation. The other options pertain to different aspects of radiation measurement. Absorbed dose corresponds to the energy deposited in any given medium (not just air), while equivalent dose takes into account the biological effect of different types of radiation by applying a weighting factor. Exposure generally refers to the amount of ionization produced in air by x-rays or gamma rays but does not express the energy deposited in a unit mass of that air like air kerma does. Understanding this distinction is crucial in radiation safety and applying appropriate protection measures in medical settings.