How is the radiation absorbed dose (Rad) defined?

The radiation absorbed dose, commonly referred to as "Rad," is defined as a unit that measures the amount of energy absorbed per unit mass of material from ionizing radiation. Specifically, one Rad is equivalent to the absorption of 100 ergs of energy per gram of matter. This definition highlights how much energy is deposited within a specific mass, making it a crucial factor in evaluating exposure to and the effects of radiation on matter, particularly biological tissues.

While other options relate to different aspects of radiation measurement—such as ionization in air, biological effects, or radioactive decay—the definition of Rad directly pertains to the energy absorbed, which is foundational for understanding radiation safety and its impact on living organisms. This concept is vital in medical physics, radiation therapy, and radiological safety, emphasizing the importance of understanding the energy transfer associated with various types of radiation exposure.