American Society of Radiologic Technologist (ASRT) Practice Exam

Which term best describes air kerma?

1. Weighted for tissue type

2. Absorbed dose

3. Kinetic energy transferred

4. Equivalent dose

The correct answer is: Kinetic energy transferred

Air kerma, which stands for "kinetic energy released per unit mass," essentially refers to the amount of energy from radiation that is transferred to air when it is exposed to this radiation. This term specifically captures the energy transferred from ionizing radiation to kinetic energy of charged particles (such as electrons) in the air. The concept is significant in radiological sciences as it helps to quantify the exposure of radiation and is crucial for understanding how various types of radiation can affect matter, particularly biological tissue. The term "kinetic energy transferred" accurately encapsulates what air kerma measures, focusing on the initial energy transfer events before any absorption by tissue or other materials occurs. In contrast, the other terms do not define air kerma accurately. For example, "absorbed dose" refers to the amount of energy absorbed per unit mass of tissue, while "weighted for tissue type" and "equivalent dose" involve considerations of tissue types and their differing sensitivities to radiation, which are not part of the direct definition of air kerma. Therefore, the characterization of air kerma as a measure of kinetic energy transferred is precise and aligns with its role in radiation measurement and safety assessments.