Becquerel (Bq) is the SI derived unit, with a special name, for radioactivity, equal to s^-1. It describes a radioactivity of an amount of radionuclide decaying at the rate, on average, of one spontaneous nuclear transition per second. The unit was named after the French scientist Antoine Henri Becquerel (1852-1908) (disintegrations per unit time), equal to s^-1.