Photon strength functions and nuclear level densities: Recent developments in photonuclear reaction studies

Photons provide a particularly clean probe for studying a wide range of nuclear structure phenomena 1. Their interaction with the nucleus is described by the electromagnetic interaction, so that the nuclear response can be separated almost model-independently from the details of the reaction mechanism. Thus, photon-induced reactions are important tools in nuclear physics for determining the properties of low-spin excited states in atomic nuclei. Important quantities for the modeling of nuclear and stellar reaction rates are photon strength functions (PSF) and nuclear level densities (NLD). Systematic studies of PSFs and NLDs across the nuclear chart are an important testing ground for benchmarking microscopic and macroscopic models, allowing extrapolation from mostly stable isotopes to experimentally unreachable exotic neutron-rich isotopes.