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Abstract

The new regime of resonant nuclear photoexcitation rendered possible by x-ray
free electron laser beams interacting with solid state targets is investigated
theoretically. Our results unexpectedly show that secondary processes coupling
nuclei to the atomic shell in the created cold high-density plasma can dominate
direct photoexcitation. As an example we discuss the case of $^{93m}$Mo isomer
depletion for which nuclear excitation by electron capture as secondary process
is shown to be orders of magnitude more efficient than the direct laser-nucleus
interaction. General arguments revisiting the role of the x-ray free electron
laser in nuclear experiments involving solid-state targets are further deduced.