What unit is typically used to measure radioactivity?

The unit typically used to measure radioactivity is the Becquerel (Bq) or the Curie (Ci). The Becquerel is defined as one disintegration per second and reflects the activity level of a radioactive source. The Curie, which is an older unit, was originally based on the radioactivity of one gram of radium-226 and is equivalent to 3.7 x 10^10 disintegrations per second. Both units specifically quantify how many radioactive decays or transformations occur in a given time period, making them the appropriate choices for measuring radioactivity.

The other units mentioned serve different purposes in the context of radiation. The Sievert (Sv) measures the biological effect of ionizing radiation on human tissue, while the Gray (Gy) measures the energy deposited by radiation in a unit mass of material. The Röntgen (R) is a measure of exposure to X-rays or gamma rays in air, which does not directly equate to the measurement of radioactivity itself.