Bq

The becquerel (symbol Bq) is the SI unit of radioactivity. It measures the activity of a radioactive source, defined as one disintegration per second. The unit is named after Antoine Henri Becquerel, who discovered spontaneous radioactivity in 1896, a finding further developed by the Curies. As a derived SI unit, the becquerel expresses the rate of nuclear decay rather than the amount of radioactive material.

In practical terms, a source with an activity of 1 Bq undergoes one radioactive decay each second on average. The becquerel is commonly used in fields such as nuclear physics, medicine, environmental monitoring, and radiation protection to quantify how intensely a material is emitting radiation. For historical reference, the curie (Ci) is a non-SI unit previously used to describe radioactivity; 1 curie equals 3.7×10^10 becquerels.

The becquerel is related to, but distinct from, radiation dose concepts. Activity describes how many decays occur per unit time, whereas dose measures the energy deposited in matter. Therefore, a high-activity source does not automatically imply a high dose without considering factors such as energy per decay, the type of radiation, exposure time, and shielding.

Commonly used multiples include the kilobecquerel (kBq) and megabecquerel (MBq) for higher activities. By providing a standardized rate of decay, the becquerel enables consistent reporting and comparison of radioactive sources across disciplines. See also curie, gray, and sievert for related concepts in radioactivity and radiation dosimetry.