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...

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The 14 N(p,γ) 15 O reaction is the slowest reaction of the carbon-nitrogen cycle of hydrogen burning and thus determines its rate. The precise knowledge of its rate is required to correctly model hydrogen burning in asymptotic giant branch stars. In addition, it is a necessary ingredient for a possible solution of the solar abundance problem by using the solar 13 N and 15 O neutrino fluxes as probes of the carbon and nitrogen abundances in the solar core. After the downward revision of its cross section due to a much lower contribution by one particular transition, capture to the ground state in 15 O, the evaluated total uncertainty is still 8%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range. The present work reports precise S-factor data at twelve energies between 0.357-1.292 MeV for the strongest transition, capture to the 6.79 MeV excited state in 15 O, and at ten energies between 0.479-1.202 MeV for the second strongest transition, capture to the ground state in 15 O. An R-matrix fit is performed to estimate the impact of the new data on astrophysical energies. The recently suggested slight enhancement of the 6.79 MeV transition at low energy could not be confirmed. The present extrapolated zero-energy S-factors are S6.79(0) = 1.24±0.11 keV barn and SGS(0) = 0.19±0.05 keV barn.

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