radguide

15 Radiation for Radionuclide Users Absorbed Dose The absorbed dose is the quantity that expresses the amount of energy which ionizing radiation imparts to a given mass of matter. The special unit for absorbed dose is the rad (Radiation Absorbed Dose), which is defined as a dose of 100 ergs of energy per gram of matter. The SI unit for absorbed dose is the gray (Gy), which is defined as a dose of one joule per kilogram. Since one joule equals 10 7 ergs, and since one kilogram equals 1000 grams, 1 Gy = 100 rad The size of the absorbed dose is dependent upon the strength (or activity ) of the radiation source, the distance from the source to the irradiated material, and the time over which the material is irradiated. The activity of the source will determine the dose rate which can be expressed in rad/hr, mrad/hr, mGy/sec, etc.