Radioactive Decay Computation with Dynamic Source Terms

This technical note discusses radioactive decay computation with multiple source terms with heterogeneous introduction dates to the system. Two methods are considered: (1) decaying in sequence from the oldest dated source, ad finitium, to the final decay date and (2) decaying each source term to the final decay date and summing the resulting nuclides. We prove that radioactive decay computation using the prescribed two methods produces the same result. The algorithmic advantage of the second method over the first one is formally argued. The radioactive decay of ⁹⁰Sr with multiple initial decay dates is given as an illustrative example.