How can I efficiently calculate the amount of material decayed after a specific time in a two-step decay chain? In my specific example, I have 56Ni -> 56Co -> 56Fe. The half life of the first process is 6.1 days, the second - 77.7 days. How can I accurately calculate the amount of 56Fe that was created after a certain time from a given quantity of 56Ni? Is there a formula for "effective half life" of such a decay, in particular when the objective is to calculate the amount of final substance created after time t, as opposed to the amount of initial substance remaining?