What is the unit of measurement for decay rate?

The decay rate of a radioactive substance is measured in units that quantify the number of decays that occur in one second. The correct answer is the Becquerel (Bq), which defines one decay per second. This unit reflects the activity of a radioactive material, providing a measure of its radioactivity.

Curies (Ci), while also a unit of radioactivity, is an older metric where 1 Ci is defined as 3.7 × 10^10 disintegrations per second. Therefore, while the Curie could indicate decay rate, the standard SI unit is the Becquerel.

Sieverts (Sv) and Grays (Gy) are units related to the effects of radiation on biological tissue (Sieverts) and the absorbed dose of radiation (Grays), respectively. Neither of these measures pertains directly to the decay rate itself, which is specifically related to the number of radioactive disintegrations occurring in a certain time frame.