who has been exposed to radiation does not become radioactive Patients emit radiation only if they have radioactive atoms on them (external contamination) or within them (internal contamination) Amounts of Radiation Geiger counters can measure amounts of radiation far below levels that have a measurable biologic effect They are inexpensive and readily available in the nuclear medicine department at most hospitals Because a Geiger counter can detect and quantify the radiation exposure rate immediately, detecting and managing a radiation hazard may be easier than detecting and managing biologic or chemical hazards Radiation exposure is commonly measured in three different units in the United States: roentgen, rad, and rem However, new international units are being used by regulatory and professional organizations ( Table 90.10 ) The roentgen (R) is a measure of radiation exposure in air Absorbed dose in an organ is measured in grays (Gy); Gy is equal to 100 rads Effective dose, in sieverts (Sv), is a measure of overall risk to an individual when the irradiation is weighted for the sensitivity of each organ to late effects of radiation One sievert is equal to 100 rems Quantity of radioactivity is measured by becquerels (Bq), defined as atomic disintegration per second The former unit, the curie (Ci), is equal to 3.7 × 1010 Bq, and mCi is equal to 37 MBq