importance in the determination of radiative neutron-capture cross sections for exotic neutron-rich nuclei. This effect could have a non-negligible impact on the neutron captures that can potentially take place in astrophysical environments characterized by high neutron densities, in particular during the r-process nucleosynthesis.

Conclusions {#sect_conc}
===========

As shown experimentally by the Oslo group, the RSF at very low $\gamma$-ray energy might be characterized by a significant enhancement with respect to the usual rapidly decreasing $\gamma$-decay strength. This upbend structure has been observed systematically in V, Sc, Fe and Mo isotopes at energies typically smaller than 3 MeV, but is absent in elements heavier than Sn. The very origin of this extra strength remains unexplained theoretically.

The impact of this upbend structure is found to be relatively small on the neutron capture cross section of stable nuclei, since it modifies the RSF in an energy region which hardly takes part in the reaction mechanism. However, for exotic neutron-rich nuclei, this effect becomes significant and could potentially increase the reaction rates of astrophysical relevance by one or even two orders of magnitude. This effect is particularly pronounced for nuclei with a low neutron separation energy, crossing a major neutron shell. This effect 