S-PROCESS AND R-PROCESS CONTRIBUTIONS TO EXTINCT RADIOACTIVITIES

There is now evidence, ranging in quality from very strong to marginal , for the existence in early solar system material of ten radionuclide s with mean lives long enough for them to be incorporated live in our planetary system but not long enough to be live at the present time. O f these ten, one (Pu-244) is unquestionably an r-process product, and four (Cs-135, Pd-107, I-129, and Hf-182) might in principle have been made by either the r-process or the s-process. One of us has construct ed a model for the history of the local part of the galaxy into which the abundances of the ten extinct nuclides can be fitted. The purpose of the present paper is to explain in greater detail the reasoning tha t has led to the assignment of I-129 to the r-process and the assignme nt of the others to the s-process. These latter assignments do not cor respond to the traditional assignments of these nuclides as primarily r-process products. It is shown that most of the so-called r-process i sobars in the solar system abundance table can have s-process contribu tions in lower mass AGB stars where peak neutron number densities of 3 x 10(9) to 3 x 10(10) cm-3 are expected during helium shell flashes.