Which statement defines an exposure rate?

• A. The dose rate in air or tissue per unit time.
• B. The total accumulated dose over a year.
• C. The dose rate in tissue per unit time.
• D. The energy deposited per unit mass in a tissue.

Answer: (A)

Exposure rate is about how fast radiation delivers exposure, i.e., a quantity that changes with time. It describes the rate at which ionizing events occur and, in practical terms, is tied to how much dose is deposited per unit time, either in air (historically defined as exposure) or in tissue after converting from exposure. That makes the statement about the dose rate per unit time, applicable to air or tissue, the best fit. The other ideas describe total dose accumulated over time, or energy deposited per mass, which are not rates and thus don’t capture the concept of exposure rate.