Short-lived radioactivities and the birth of the Sun

Now extinct short-lived radioactive isotopes were apparently extant in the early solar system. Their abundances can be inferred from isotopic effects in their daughter nuclei in primitive meteorites, and the deviation of these abundances from expectations from continuous galactic nucleosynthesis yields important information on the last nucleosynthetic events that contributed new nuclei to the solar system and on the general circumstances of the Sun's birth. In this paper we present a rudimentary model that attempts to reconcile the abundances of ten short-lived radioactivities in the early solar system. In broad outlines, the picture requires 1) that Type Ia supernovae maintained a steady ISM supply of Mn-53 and Sm-146, 2) that the r- process events that slowly admixed new Pd-107, I-129, Hf-182, and Pu-244 nuclei to the solar system occurred over an interval of several hundred million years prior to solar system formation, and 3) that a massive star, by injecting only material outside its helium-exhausted core into the proto-solar nebula, contributed Al-26, Cl-36, Ca-41, Fe-60, and Hf-182 no more than one million years prior to the Sun's birth. In this picture, the live Hf-182 present in the early solar system was not due to r-process production but rather to a fast s-process in helium or carbon burning shell in the massive star. We conclude with a possible chemical-memory explanation for the putative Cr-53/Cr-52 gradient in the solar system.