Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions

We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and 208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that the description of low-lying magnetic states of doubly-closed-shell nuclei imposes severe constraints on the spin and tensor terms of the nucleon-nucleon effective interaction. We have first made an investigation by using four phenomenological effective interactions and we have obtained good agreement with the experimental magnetic spectra, and, to a lesser extent, with the electron scattering responses. Then we have made self-consistent RPA calculations to test the validity of the finite-range D1 Gogny interaction. For all the nuclei under study we have found that this interaction inverts the energies of all the magnetic states forming isospin doublets.Comment: 19 pages, 13 figures, 7 tables, accepted for publication in Phys. Rev.

Collective Excitations of (154)Sm nucleus at FEL{gamma}+LHC Collider

The production of collective excitations of the (154)Sm at FEL{gamma}+LHC collider is investigated. We show that this machine will be a powerful tool for investigation of high energy level excitations.Comment: 6 pages, 1 figure, 4 table

Tensor effective interaction in self-consistent Random Phase Approximation calculations

We present a study of the effects of the tensor-isospin term of the effective interaction in Hartree-Fock and Random Phase Approximation calculations. We used finite-range forces of Gogny type, and we added to them a tensor-isospin term which behaves, at large internucleonic distances, as the analogous term of the microscopic interactions. The strength of this tensor force has been chosen to reproduce the experimental energy of the lowest 0$^-$ excited state in $^{16}$O, which shows large sensitivity to this term of the interaction. With these finite-range interactions, we have studied the effects of the tensor-isospin force in ground and excited states of carbon, oxygen, calcium, nickel, zirconium, tin and lead isotopes. Our results show that the tensor force affects mainly the nucleon single particle energies. However, we found some interesting cases where also bulk nuclear properties are sensitive to the tensor interaction.Comment: 18 pages, 14 figures, 3 table

Pygmy dipole strength close to particle-separation energies - the case of the Mo isotopes

The distribution of electromagnetic dipole strength in 92, 98, 100 Mo has been investigated by photon scattering using bremsstrahlung from the new ELBE facility. The experimental data for well separated nuclear resonances indicate a transition from a regular to a chaotic behaviour above 4 MeV of excitation energy. As the strength distributions follow a Porter-Thomas distribution much of the dipole strength is found in weak and in unresolved resonances appearing as fluctuating cross section. An analysis of this quasi-continuum - here applied to nuclear resonance fluorescence in a novel way - delivers dipole strength functions, which are combining smoothly to those obtained from (g,n)-data. Enhancements at 6.5 MeV and at ~9 MeV are linked to the pygmy dipole resonances postulated to occur in heavy nuclei.Comment: 6 pages, 5 figures, proceedings Nuclear Physics in Astrophysics II, May 16-20, Debrecen, Hungary. The original publication is available at www.eurphysj.or

Concentration of electric dipole strength below the neutron separation energy in N = 82 nuclei

The semi-magic nuclei Ba-138, Ce-140, and Sm-144 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.Comment: 10 pages, 3 figure

Performance metrics and auditing framework using application kernels for high‐performance computer systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97468/1/cpe2871.pd

Photon scattering studies of the giant dipole resonance in medium weight nuclei

Quasimonochromatic photons have been used to measure elastic and inelastic photon scattering cross sections in the giant dipole resonance region of 52Cr, Fe, 60Ni, 92Mo, and 96Mo in an experiment in which the elastic and inelastic scattering are resolved. The elastic scattering cross sections show clear evidence for isospin splitting of the giant dipole resonance. The inelastic scattering to low-lying vibrational levels, which is a measure of the coupling between the giant dipole resonance and collective surface vibrations, is in qualitative agreement with the predictions of the dynamic collective model. However, when examined in detail, this model does not provide an adequate description of the scattering data

Isospin Asymmetry in Nuclei and Neutron Stars

The roles of isospin asymmetry in nuclei and neutron stars are investigated using a range of potential and field-theoretical models of nucleonic matter. The parameters of these models are fixed by fitting the properties of homogeneous bulk matter and closed-shell nuclei. We discuss and unravel the causes of correlations among the neutron skin thickness in heavy nuclei, the pressure of beta-equilibrated matter at a density of 0.1 fm$^{-3}$, the derivative of the nuclear symmetry energy at the same density and the radii of moderate mass neutron stars. Constraints on the symmetry properties of nuclear matter from the binding energies of nuclei are examined. The extent to which forthcoming neutron skin measurements will further delimit the symmetry properties is investigated. The impact of symmetry energy constraints for the mass and moment of inertia contained within neutron star crusts and the threshold density for the nucleon direct Urca process, all of which are potentially measurable, is explored. We also comment on the minimum neutron star radius, assuming that only nucleonic matter exists within the star.Comment: 49 pages, 17 figures, Phys. Rep. (in press); made improvements to "RAPR" and corrected transition densitie

A Measurement of the Interference Structure Function, R_LT, for the 12C(e,e'p) reaction in the Quasielastic Region

The coincidence cross-section and the interference structure function, R_LT, were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and central momentum transfer of q=400 MeV/c. The measurement was at an opening angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to 65 MeV. The R_LT structure function is found to be consistent with zero for E_m > 50 MeV, confirming an earlier study which indicated that R_L vanishes in this region. The integrated strengths of the p- and s-shell are compared with a Distorted Wave Impulse Approximation calculation. The s-shell strength and shape are compared with a Hartree Fock-Random Phase Approximation calculation. The DWIA calculation overestimates the cross sections for p- and s-shell proton knockout as expected, but surprisingly agrees with the extracted R_LT value for both shells. The HF-RPA calculation describes the data more consistently, which may be due to the inclusion of 2-body currents in this calculation.Comment: 8 Pages LaTex, 5 postscript figures. Submitted to Phys. Rev.