What is the SI unit of the absorbed dose?

The absorbed dose is defined as the amount of energy deposited by ionizing radiation in a substance per unit mass of that substance. In the International System of Units (SI), this is quantified using the Gray (Gy) as the unit. One gray is equivalent to the absorption of one joule of radiation energy by one kilogram of matter. This measurement is critical in fields such as radiology and radiation therapy, where understanding the exact amount of radiation that tissues absorb is essential for ensuring safety and effectiveness in treatment.

The other units mentioned serve different purposes: the sievert is used to measure the biological effects of radiation and accounts for the type of radiation and its impact on human tissues; the rad is a traditional unit that has been mostly replaced by the gray in modern practice; the rem is similar to the sievert but is also used to express the biological effects of radiation based on the type of radiation and the susceptibility of different tissues. Hence, while they are all related to radiation measurement, the Gray is specifically the SI unit designated for absorbed dose.