Multiple sources or late injection of short-lived r-nuclides in the early solar system?

Comparisons between the predicted abundances of short-lived r -nuclides ( 107 Pd, 129 I, 182 Hf, and 244 Pu) in the interstellar medium (ISM) and the observed abundances in the early solar system (ESS) conclusively showed that these nuclides cannot simply be derived from galactic chemical evolution (GCE) if synthesized in a unique stellar environment. It was thus suggested that two different types of stars were responsible for the production of light and heavy r -nuclides. Here, new constraints on the 244 Pu / 238 U production ratio are used in an open nonlinear GCE model. It is shown that the two r -process scenario cannot explain the low abundance of 244 Pu in the ESS and that this requires either than actinides be produced at an additional site (A-events) or more likely, that 129 I and 244 Pu be inherited from GCE and 107 Pd and 182 Hf be injected in the ESS by the explosion of a nearby supernova.