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Dipole strength of 181Ta for the evaluation of the 180Ta stellar neutron capture rate

Makinaga, A.; Massarczyk, R.; Schwengner, R.; Beard, M.; Dönau, F.; Anders, M.; Bemmerer, D.; Beyer, R.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kögler, T.; Röder, M.; Schmidt, K.; Wagner, A.


The photoabsorption cross section of 181Ta 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 gamma-ray spectra includes the quasicontinuum of levels at high energy. Simulations of gamma-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-random phase approximation in a deformed basis. A combination of the present experimental data and (gamma,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 180mTa.

Keywords: Nuclear resonance fluorescence; photon scattering; photoabsorption cross section; dipole strength function; astrophysical reaction rates; statistical reaction model; quasiparticle random phase approximation; nuclear deformation

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