Sievert is a measure of ionizing radiation. It is used to quantify the amount of radiation that an organism is exposed to. There are different units that can be used interchangeably with sievert, depending on the context of its use. These units include becquerel, gray, and rem. Becquerel is used to measure the radioactive decay rate of a substance, while gray is used to measure the amount of absorbed radiation. Rem is used in the United States to measure the biologically effective dose of ionizing radiation. Although these units can be used interchangeably, sievert is the standard unit of measurement in the International System of Units (SI).