The semi-magic nuclei 138 Ba, 140 Ce, and 144 Sm have been investigated in photon scattering experiments up to an excitation energy of about 10 MeV. The distribution of the electric dipole strength shows a resonance like structure at energies between 5.5 and 8 MeV exhausting up to 1 % of the isovector E1 Energy Weighted Sum Rule.

High precision angular distribution data of (α,α) A systematic fitting procedure was applied to the presented experimental scattering data to obtain comprehensive local potential parameter sets which are composed of a real folding potential and an imaginary potential of Woods-Saxon surface type. The obtained potential parameters were used in turn to construct a new systematic α-nucleus potential with very few parameters.Although this new potential cannot reproduce the angular distributions with the same small deviations as the local potential, the new potential is able to predict the total reaction cross sections for all cases under study.

Differential cross sections for 3 He-α scattering were measured in the energy range up to 3 MeV. These data together with other available experimental results for 3 He +α and 3 H +α scattering were analyzed in the framework of the optical model using double-folded potentials. The optical potentials obtained were used to calculate the astrophysical S-factors of the capture reactions 3 He(α, γ) 7 Be and 3 H(α, γ) 7 Li, and the branching ratios for the transitions into the two final 7 Be and 7 Li bound states, respectively. For 3 He(α, γ) 7 Be excellent agreement between calculated and experimental data is obtained. For 3 H(α, γ) 7 Li a S(0) value has been found which is a factor of about 1.5 larger than the adopted value. For both capture reactions a similar branching ratio of R = σ(γ 1 )/σ(γ 0 ) ≈ 0.43 has been obtained.

The cross sections for the elastic scattering reactions 112,124 Sn(α,α) 112,124 Sn at energies above and below the Coulomb barrier are presented and compared to predictions for global α-nucleus potentials. The high precision of the new data allows a study of the global α-nucleus potentials at both the proton and neutron-rich sides of an isotopic chain. In addition, local α-nucleus potentials have been extracted for both nuclei, and used to reproduce elastic scattering data at higher energies. Predictions from the capture cross section of the reaction 112 Sn(α,γ) 116 Te at astrophysically relevant energies are presented and compared to experimental data.

For the determination of the 144 Sm-α optical potential we measured the angular distribution of 144 Sm(α,α) 144 Sm scattering at the energy E lab = 20 MeV with high accuracy. Using the known systematics of α-nucleus optical potentials we are able to derive the 144 Sm-α optical potential at the astrophysically relevant energy Ec.m. = 9.5 MeV with very limited uncertainties.