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New results on dipole strength distributions of direct and cascade transitions in neutron-excess nuclei, obtained in a theoretical approach based on energy-density functional theory and quasiparticle-phonon model are discussed [1]. The method and its recent developments, including a reaction theory [2, 3], have been successfully applied in spectroscopic studies of different types of nuclear excitations in stable and exotic nuclei, including two-phonon states [4], pygmy and giant resonances [1-5], thus demonstrating its effectiveness and reliability. Besides the single-particle nature of the excited nuclear states from the PDR region, different properties of the low-energy dipole strength emerge from the analysis of inelastic photon- and proton-scattering spectral distributions and branching ratios, from which the role of the quasicontinuum coupling with the low-energy dipole strength can be studied [5]. Experimentally, the determination of the dipole strength function and the associated photoabsorption cross section requires knowledge of the intensity distribution of the ground state transitions and their branching ratios. These quantities cannot be derived directly from the measured spectra. However, they can be determined theoretically from our microscopic calculations, which are also important for the interpretation of the fine structure of the dipole photoabsorption cross-section in atomic nuclei.
[1] N. Tsoneva, H. Lenske, Physics of Atomic Nuclei 79, 885–903 (2016) and refs. therein.
[2] M. Spieker, A. Heusler, B.A. Brown, T. Faestermann, R. Hertenberger, G. Potel, M. Scheck, N.Tsoneva, M. Weinert, H.-F. Wirth, and A. Zilges, Phys. Rev. Lett. 125, 102503 (2020).
[3] M. Weinert, M. Spieker, G. Potel, N. Tsoneva, M. Müscher, J. Wilhelmy, and A. Zilges, Phys. Rev. Lett. 127, 242501 (2021).
[4] J. Isaak, D. Savran, N. Pietralla, N. Tsoneva, A. Zilges, K. Eberhardt, C. Geppert, C. Gorges, H. Lenske, and D. Renisch, Phys. Rev. C 108, L051301 (2023).
[5] T. Shizuma, S. Endo, A. Kimura, R. Massarczyk, R. Schwengner, R. Beyer, T. Hensel, H. Hoffmann, A. Junghans, K. Römer, S. Turkat, A. Wagner, and N. Tsoneva, Phys. Rev. C 106, 044326 (2022).
