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The electromagnetic dipole strength of the nucleus 136 Ba has been investigated. Two measurements were performed with electron energies of 7.0 and 11.4 MeV at the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. Photon scattering experiments on the same nucleus have been performed at the HIγS facility of the Triangle Universities Nuclear Laboratory between 4.7 and 9.3 MeV. The GEANT4 code has been used to determine detector response and non-nuclear scattered events. Thus it is possible to account for the dipole strength in the quasi-continuum of unresolvable transitions. A statistical code was used to simulate inelastic transitions and to determine the branching ratios of transitions to the ground-state. The resulting photoabsorption cross section is compared to QRPA and RQTBA calculations.

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The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A = 124, 128, 132, and 134 in nuclear resonance fluorescence experiments using the γELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIγS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides. Photon strength functions (PSF) are important inputs for statistical reaction codes applied in network calculations in nuclear astrophysics and in simulations done for nuclear power production and safety. Knowing and understanding the behavior of the PSF in the energy region around and below the neutron threshold is essential for these applications. For the dominating electric dipole (E1) part of the PSF, the RIPL3 compilation of the IAEA [1] offers an overview on various models, which in essence base on the concept of the damped isovector E1 giant dipole resonance (GDR). It is described by one or two Lorentzian functions with parameters fitted to the characteristic resonance structure observed in (γ, n) reactions. For open shell nuclei, which constitute the majority, the nuclear deformation is taken into account. It splits the peak of the GDR [2, 3] and, as a consequence, increases the dipole strength distribution in the region below the neutron-separation energy. Along these lines, a new global description of the PSF was recently presented in Ref.[4], which takes triaxial quadrupole deformation into account and which is called triple Lorentzian model (TLO).Experimental and theoretical studies [5][6][7][8][9], which have been recently reviewed by Savran, Aumann, and Zilges [10] suggest a richer structure of the PSF below the neutron-separation energy than accounted for by the Lorentzian-type models. In this letter we follow the suggestion in the review [10]: "Today the term Pygmy Dipole Resonance (PDR) is frequently used for the low-lying E1 strength and we will follow this notation in this review without implying with this notation any further interpretation of its structure." The rational behind this terminology is that the interpretation of the PDR depends strongly on the theoretical model invoked and present day experiments cannot distinguish between the models. One important aspect of studying the PDR concerns its isospin dependence, which is particularly important for simulating the r-process that d...