Inclusion of isomers/astromers in s-process nucleosynthesis: the pivotal case of 85Kr
J. Tannous, J. Tannous, G. W. Misch, M. Mumpower, B. S. Meyer, B. Meyer, F. X. Timmes, F. Timmes, A. J. Couture, C. L. Fryer, C. Fryer
Published ApJ 986 107 (2025)
85-Kr is an s-process branch point nucleus: the competition between neutron capture and β decay influences the production of nearby nuclides. Its evolution is complicated by the existence of a long-lived isomer that β-decays on a much shorter timescale than the ground state. We calculate the effective thermal transition rates between the ground and isomeric states along with estimates of their thermal β-decay rates in a suite of nucleosynthesis computations to assess the consequences of this isomer on isotopic abundances. A central finding in this study is that the s-process flow with the isomer included under astrophysical conditions relevant for the s-process creates a shift in abundance yield of the important radioactivity 87-Rb by a factor of ∼2.4 relative to the case when the 85-Kr is taken to be internally equilibrated when neutron exposures approach the main branch limit. On the other hand, the 88-Sr/86-Sr ratio is little affected because the bulk of the flow through 85-Kr is still via beta decay, whether the isomer is taken into account or not.