SI unit of activity of a radioactive substance
The becquerel (symbol Bq) is the SI derived unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second. A petabecquerel is 1015 times a becquerel, s-1, s for second, dimensionally is it second minus one, i.e. inverse seconds.
The unit is named in honor of Henri Becquerel.