103Ru has a 39-day half life. 134Cs has a 2 yr half life, 137Cs has a 30-year half life. 131I has an 8 day half-life. One can use those numbers to infer, in t

103Ru has a 39-day half life. 134Cs has a 2 yr half life, 137Cs has a 30-year half life. 131I has an 8 day half-life. One can use those numbers to infer, in the absence of supporting chains, how-recently the released material was involved in a fission reaction.