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 Be-10 and Ca-41 at levels compatible with a homogeneous distribution over the entire protoplanetary disk up to the comet-forming region. Mn-53 and Cl-36 cannot be produced at canonical levels together with Be-10 and Ca-41, unless we posit a heterogeneous spatial distribution. The high level of Be-7 suggested recently is barely compatible with a coproduction of Be-10 up to the cometary reservoir and may indicate the irradiation of a gas phase. Finally, we show that the maximum amount of irradiation-induced Al-26 can only account for a homogeneous distribution of this radionuclide over a rocky reservoir of 2-3 M-circle plus and that the well-defined canonical Al-26/Al-27 ratio observed in Ca-Al-rich inclusions is probably not compatible with an in situ production in the embedded phase of the Sun. If extinct Al-26 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.