Energetic Constraints on In Situ Production of Short-Lived Radionuclei in the Early Solar System

We calculate upper limits on the amount of short-lived radionuclei that can be produced by nonthermal nucleosynthesis in the early solar system. Using energetic constraints obtained from X-ray observations of young stellar objects, we show that irradiation of bare solids can produce super(10)Be and super(41)Ca at levels compatible with a homogeneous distribution over the entire protoplanetary disk up to the comet-forming region. super(53)Mn and super(36)CI cannot be produced at canonical levels together with super(10)Be and super(41)Ca, unless we posit a heterogeneous spatial distribution. The high level of super(7)Be suggested recently is barely compatible with a reproduction of super(10)Be up to the cometary reservoir and may indicate the irradiation of a gas phase. Finally, we show that the maximum amount of irradiation-induced super(26)AI can only account for a homogeneous distribution of this radionuclide over a rocky reservoir of 2-3 M [unk] and that the well-defined canonical super(26)AI/ super(27) AI ratio observed in Ca-AI-rich inclusions is probably not compatible with an in situ production in the embedded phase of the Sun. If extinct super(26)AI is detected in the cometary material from the Stardust mission, the nucleosynthetic process that produced this preeminent high-resolution chronometer should be searched for in stellar events contemporary with the birth of the Sun.