The becquerel (symbol Bq) is the SI derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. It is therefore equivalent to s−1. The becquerel is named for Henri Becquerel, who shared a Nobel Prize with Pierre and Marie Curie for their work in discovering radioactivity. In a fixed mass of radioactive material, the number of becquerels changes with time. Therefore, a sample radioactive decay rate is always… (More on Becquerel)