Protostellar cosmic rays and extinct radioactivities in meteorites

Calcium-aluminum-rich inclusions (CAIs) and chondrules of chondritic meteor ites may originate with the melting of dustballs launched by a magnetically driven bipolar outflow from the inner edge of the primitive solar nebula. Bombardment by protostellar cosmic rays may make the rock precursors of CAI s and chondrules radioactive, producing radionuclides found in meteorites t hat are difficult to obtain with other mechanisms. Reasonable scalings from the observed hard X-rays for the cosmic-ray protons released by flares in young stellar objects yield the correct amounts of Ca-41, Mn-53, and La-138 inferred for meteorites, but proton- and alpha-induced transformations und erproduce Al-26 by a factor of about 20. The missing Al-26 may be synthesiz ed by He-3 nuclei accelerated in impulsive flares reacting primarily with M g-24, an abundant isotope in the target precursor rocks. The mechanism allo ws a simple explanation for the very different ratios of Al-26/Al-27 inferr ed for normal CAIs, CAIs with fractionated and unidentified nuclear (FUN) a nomalies, and chondrules. The overproduction of Ca-41 by analogous He-3 rea ctions and the case of Fe-60 inferred for eucritic meteorites require speci al interpretations in this picture.