What is defined as the energy imparted by ionizing radiation per unit mass of irradiated material?

The term that defines the energy imparted by ionizing radiation per unit mass of irradiated material is "Absorbed Dose." This concept is critical in the field of radiation safety and radiological protection because it quantifies the amount of energy deposited by radiation in a specific mass of material, typically expressed in grays (Gy).

Absorbed dose provides a direct measurement of the biological effects of radiation on the tissues it interacts with, making it an essential parameter when assessing potential health impacts. Understanding absorbed dose helps professionals evaluate radiation exposure's potential risks, particularly in medical imaging and radiation therapy.

The other terms mentioned have different meanings: "Radiation Exposure" refers to the amount of ionization produced in air by X or gamma radiation, measured in roentgens (R); "Radiation Dose" is a more general term that can refer to different types of measures of radiation impact; and "Effective Dose" is a calculation that accounts for the type of radiation and the sensitivity of different organs to radiation, expressed in sieverts (Sv) but not limited to just the energy imparted per unit mass. Thus, "Absorbed Dose" specifically pinpoints the energy deposition aspect, making it the correct answer.