The amount of radiation damage in human exposure to ionizing radiation is measured in terms of:

The correct answer, Sieverts, measures the effect of ionizing radiation on human health. While the Grays (Gy) measure the absorbed dose of radiation, Sieverts account for the biological impact of that radiation based on the type of radiation and the sensitivity of different tissues. This is crucial because not all ionizing radiation has the same potential to cause harm; for example, alpha particles are more damaging than beta particles for the same amount of energy absorbed.

By considering the relative biological effectiveness, Sieverts allow for a better understanding of the potential long-term effects of radiation exposure on human health, factoring in various types of radiation and the biological systems involved. This makes it the standard unit used in assessing radiation exposure for health risk assessments and regulatory purposes.