11 Radioactive Decay Radioactive atoms are unstable because they have too much energy When they release their extra energy they are said to decay When studying cesium 137 a nuclear engineer found that over 365 days 1 000 000 radioactive atoms decayed to 977 287 radioactive atoms therefore 22 713 atoms decayed during 365 days 2 Find the mean number of radioactive atoms that decayed in a day Find the probability that on a given day exactly 50 radioactive atoms decayed murde