A new class of models is advanced for interpreting the relationship of radioactive abundances in the early solar system to their average concentration in the interstellar medium. The model assumes that fresh radioactivities are ejected from supernovae into the hot interstellar medium, and that the time scales for changes of phase into molecular clouds determine how much survives for formation therein of our solar system. A more realistic and physically motivated understanding of the low observed concentrations of 129I, 244Pu, and 107Pd may result.