Modification of nuclear transitions in stellar plasma by electronic processes: K isomers in 176Lu and 180Ta under s-process conditions

The influence of the stellar plasma on the production and destruction of K isomers is studied for the examples Lu-176 and Ta-180. Individual electromagnetic transitions are enhanced predominantly by nuclear excitation by electron capture, whereas the other mechanisms of electron scattering and nuclear excitation by electron transition give only minor contributions. It is found that individual transitions can be enhanced significantly for low transition energies below 100 keV. Transitions with higher energies above 200 keV are practically not affected. Although one low-energy transition in Ta-180 is enhanced by up to a factor of 10, the stellar transition rates from low-K to high-K states via so-called intermediate states in Lu-176 and Ta-180 do not change significantly under s-process conditions. The s-process nucleosynthesis of Lu-176 and Ta-180 remains essentially unchanged.