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Abstract

In the process of slow neutron capture nucleosynthesis, one often has to take into account that nuclei undergoing neutron capture and beta decay may not be only in their ground states, but also in long-lived excited states, known as nuclear isomers. Such isomers might not be thermally equilibrated with the nuclear ground states. In this thesis, we theoretically investigate the efficiency of nuclear excitation by electron capture (NEEC) to deplete such isomeric states in dense stellar plasmas under the sprocess conditions. Due to the high charge states available in such plasmas, NEEC is not always accompanied by its detailed-balance counterpart, the inverse process internal conversion, and reaction rates can be considered separately. We investigate the cases of ^58m Co, ^99mTc, ^121mSn, ^121mSb and ^152mEu and compare the NEEC depletion rates with relevant beta and gamma decay rates of the isomeric states. The results for 58mCo, ^121mSb and ^152mEu show that NEEC should be considered as relevant isomer depletion channel in astrophysical plasmas.