the amount of radiation an object (such as human tissue) receives. Several units are used to describe radiation doses, as listed below.
rad (acronym for radiation absorbed dose) – a basic unit of the amount of radiation transferred to an object. This measurement does not take into account the type of radiation, which can influence the effect on different body tissues. The rad has largely been replaced by the gray measurement scale (see next).
gray (abbreviated Gy) – the newer, international unit of measurement of radiation transfer. One gray equals 100 rads, and a centigray is 1/100th of a gray. So, one rad equals one centigray (cGy). 1/1000 of a gray is called a milligray (mGy).
rem (acronym for roentgen equivalent man) – a basic unit of radiation exposure which is based on both the dose and the type of radiation. Because of this, it is more commonly used to describe radiation exposure in humans than is the rad. Often reported in units of millirem (mrem), which is 1/1000 of a rem. The rem is sometimes replaced by the sievert (see next).
sievert (see-vert) – abbreviated Sv. A newer, international unit of measurement of human radiation exposure. One sievert equals 100 rem. Often reported in millisieverts (mSv), which are thousandths of a sievert (or 1/10 of a rem).