Which SI unit is associated with dose equivalent?

The unit associated with dose equivalent is the Sievert. Dose equivalent is a measure used in radiation protection to account for the biological effects of different types of radiation on human tissue. It takes into consideration the energy deposited by radiation and the quality of that radiation type, which can affect the level of biological damage it can cause.

The Sievert quantifies the effect of radiation on human health, allowing for comparisons between different radiation exposures. This unit incorporates a radiation weighting factor, which helps in assessing the potential biological impacts from various radiation types, such as alpha particles, beta particles, gamma rays, and neutrons.

In contrast, other units listed relate to different concepts in radiation measurement. For example, the Gray measures the absorbed dose of radiation, representing the energy deposited in tissue, but it does not account for the biological effectiveness of that radiation. The Röntgen is primarily used to measure exposure to ionizing radiation in air, and the Rad is an older unit of absorbed dose which has been largely replaced by the Gray. Therefore, while all these units are related to radiation, the Sievert uniquely represents the biological impact of radiation, making it the correct answer.