Becquerel A.H. Becquerel The becquerel (Bq) is the unit of activity (A). It is named after the French physicist Antoine Henri Becquerel (1852 - 1908). becquerel (Bq) = disintegration per second (s) Note that activity and frequency (ν) share the same unit (s-1). However, activity is a stochastic quantity, whereas frequency is a periodic quantity.