Enhanced electric dipole strength below particle-threshold as a consequence of nuclear deformation


Enhanced electric dipole strength below particle-threshold as a consequence of nuclear deformation

Rusev, G.; Schwengner, R.; Beyer, R.; Erhard, M.; Grosse, E.; Junghans, A. R.; Kosev, K.; Nair, C.; Schilling, K. D.; Wagner, A.; Dönau, F.; Frauendorf, S.

Photoabsorption cross sections up to the neutron-separation energy were measured for the stable even-mass isotopes 92-100Mo in photon-scattering experiments. The photon-scattering data were analyzed in a novel way by taking into account the intensity of unresolved levels at high excitation energy and high level density. Simulations of gamma-ray cascades were performed to estimate the intensity distribution of inelastic transitions to low-lying levels and, hence, to deduce intensities and branching ratios of the ground-state transitions needed for the determination of the absorption cross section. The present (gamma,gamma') data can be combined for the first time with (gamma,n) data which allows us to obtain the absorption cross section in the energy range from about 4 MeV up to the giant dipole resonance for a series of isotopes. The absorption cross section below the neutron-separation energy increase with the number of neutrons above the neutron shell closure at N = 50. Calculations using a quasiparticle-random-phase approximation in a deformed Woods-Saxon potential describe this effect as a consequence of the increasing nuclear deformation.

Keywords: photon scattering; photoabsorption cross section; dipole strength function; nuclear deformation; random phase approximation

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Publ.-Id: 11269