No abstract

The γ -ray strength function is an important input quantity for the determination of the photoreaction rate and the neutron capture rate for astrophysics as well as for nuclear technologies. To test model predictions, the photoabsorption cross section of 139 La up to the neutron-separation energy was measured using bremsstrahlung produced at the electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf with an electron beam of 11.5 MeV kinetic energy. The experimental data were analyzed by applying Monte Carlo simulations of γ -ray cascades to obtain the intensities of the ground-state transitions and their branching ratios. We found a significant enhancement of electric dipole strength in the energy range from 6 to 10 MeV that may be related with a pygmy dipole resonance. The present data are combined with photoneutron cross sections for 139 La and compared with results of calculations on the basis of a quasiparticle-random-phase approximation using an instantaneous-shape sampling.

Cross sections of the 186 W, 187 Re, 188 Os(γ, n) reactions were measured using quasi-monochromatic photon beams from laser Compton scattering (LCS) with average energies from 7.3 to 10.9 MeV. The results are compared with the predictions of Hauser-Feshbach statistical calculations using four different sets of input parameters. In addition, the inverse neutron capture cross sections were evaluated by constraining the model parameters, especially the E1 strength function, on the basis of the experimental data. The present experiment helps to further constrain the correction factor Fσ for the neutron capture on the 9.75 keV state in 187 Os. Implications of Fσ to the Re-Os cosmochronology are discussed with a focus on the uncertainty in the estimate of the age of the Galaxy.PACS numbers: PACS number(s): 25.40.Lw,26.20.+f

Photoneutron cross sections were measured for 91Zr, 92Zr, and 94Zr near the neutron separation energy with quasimonochromatic gamma rays. The data exhibit some extra components around the neutron threshold. A coherent analysis of the photoneutron data for 92Zr together with the neutron capture on 91Zr based on the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model for the E1 strength has revealed the presence of an M1 resonance at 9 MeV. The microscopic approach systematically shows the same M1 strength in the photoneutron cross section for 91Zr and 94Zr. The total M1 strength is about 75% larger than the strength predicted by the systematics, being qualitatively consistent with the giant M1 resonance observed in the inelastic proton scattering.

The photoabsorption cross section of 181 Ta up to the neutron-separation energy is deduced using bremsstrahlung produced with an electron beam of 9.6 MeV energy. The analysis of the measured γ -ray spectra includes the quasicontinuum of levels at high energy. Simulations of γ -ray cascades are performed to estimate intensities of inelastic transitions and branching ratios of the ground-state transitions. The resulting photoabsorption cross section shows enhanced dipole strength in the energy range from 5 to 8 MeV, which may be related to a pygmy dipole resonance. The results of the present experiment are compared with predictions of a quasiparticle-randomphase approximation in a deformed basis. A combination of the present experimental data and (γ,n) data is used as an input to the statistical code TALYS applied to calculate cross sections and reaction rates of photonuclear reactions that are important for the nucleosynthesis of 180 Ta.A. MAKINAGA et al. PHYSICAL REVIEW C 90, 044301 (2014)