E. Khan

Large-scale QRPA calculation of E1-strength and its impact on the neutron capture cross section

Abstract Large-scale QRPA calculations of the E1-strength are performed as a first attempt to microscopically derive the radiative neutron capture cross sections for the whole nuclear chart. A folding procedure is applied to the QRPA strength distribution to take the damping of the collective motion into account. It is shown that the resulting E1-strength function based on the SLy4 Skyrme force is in close agreement with photoabsorption data as well as the available experimental E1 strength at low energies. The increase of the E1-strength at low energies for neutron-rich nuclei is qualitatively analyzed and shown to affect the corresponding radiative neutron capture cross section significantly. Axa0complete set of E1-strength function is made available for practical applications in a table format for all 8⩽ Z ⩽110 nuclei lying between the proton and the neutron drip lines.

Microscopic HFB+QRPA predictions of dipole strength for astrophysics applications

Abstract Large-scale QRPA calculations of the E1-strength are performed on top of HFB calculations in order to derive the radiative neutron capture cross sections for the whole nuclear chart. The HFB + QRPA predictions based on various Skyrme forces with different pairing prescriptions and parameterizations are confronted with experimental photoabsorption data for spherical nuclei. Within the approximations of the present model, the effective nucleon–nucleon interaction is probed with the GDR data. The dipole strengths obtained with the present HFB + QRPA model is finally used to estimate the radiative neutron capture cross section for all nuclei of relevance in astrophysics applications. The resulting rates are shown to be close to the one predicted with the previously determined HFBCS + QRPA model, but for neutron-rich nuclei to differ significantly from the ones obtained with the empirical Lorentzian-like formula.

Low-lying collective states in neutron-rich oxygen isotopes via proton scattering ☆

Abstract Proton elastic and inelastic scattering angular distributions to the 2+1 and the 3−1 states for the neutron-rich nucleus 20 O were measured with a secondary beam using the MUST silicon strip detector array. Data for 18 O were also obtained for comparison. A phenomenological analysis has been used to deduce the deformation parameters βp,p′ for the collective excitations. Matter and transition densities were generated from self-consistent QRPA calculations. DWBA calculations using microscopic optical potentials obtained with these densities and the JLM interaction are compared to the data. The isovector character of the 2+1 state in 20 O is confirmed and predictions are discussed for the properties of the heavier neutron-rich oxygen isotopes.

Low-lying 2+ states in neutron-rich oxygen isotopes in quasiparticle random phase approximation

Abstract The properties of the low-lying, collective 2 1 + states in neutron-rich oxygen isotopes are investigated in the framework of self-consistent microscopic models with effective Skyrme interactions. In RPA the excitation energies E 2 + 1 can be well described but the transition probabilities are much too small as compared to experiment. Pairing correlations are then accounted for by performing quasiparticle RPA calculations. This improves considerably the predictions of B ( E 2) values and it enables one to calculate more reliably the ratios M n / M p of neutron-to-proton transition amplitudes. A satisfactory agreement with the existing experimental values of M n / M p is obtained.

Proton scattering from the unstable nuclei 30S and 34Ar: structural evolution along the sulfur and argon isotopic chains☆

Abstract Proton elastic and inelastic scattering angular distributions to the 2 1 + and 3 1 − collective states of the proton-rich nuclei 30 S and 34 Ar were measured at 53xa0MeV/ A and 47xa0MeV/ A , respectively, using secondary beams from the GANIL facility and the MUST silicon strip detector array. Data for the stable 32 S nucleus were also obtained at 53xa0MeV/ A for comparison. A phenomenological analysis was used to deduce the deformation parameters β p,p′ for the low-lying collective excitations. A microscopic analysis was performed by generating matter and transition densities from self-consistent QRPA calculations. Configuration mixing calculations based on a collective Bohr Hamiltonian were also performed. DWBA and coupled-channel calculations using microscopic optical potentials built from these densities and the JLM interaction are compared to the data. There is no indication for the presence of proton skins in these nuclei. The microscopic calculations are extended to the even–even sulfur and argon isotopes from A =30 to A =40, and A =34 to A =44, respectively, and compared to available experimental results. On the basis of this analysis predictions are made for the 42,44 S and 46 Ar nuclei concerning ground state and transition densities.

Folding model analysis of elastic and inelastic proton scattering on sulfur isotopes

Abstract The folding formalism for the nucleon–nucleus optical potential and inelastic form factor is applied to study elastic and inelastic proton scattering on 30–40S isotopes. A recently developed realistic density dependent M3Y interaction, well tested in the folding analysis of nucleus–nucleus elastic and inelastic scattering, is used as effective NN interaction. The nuclear ground state and transition densities (for the 2+ excitations in sulfur isotopes) are obtained in the Hartree–Fock-BCS and QRPA approaches, respectively. The best fit ratios of transition moments Mn2+/Mp2+ for the lowest 2+ states in sulfur isotopes are compared to those obtained earlier in the DWBA analysis of the same data using the same structure model and inelastic form factors obtained with the JLM effective interaction. Our folding + DWBA analysis has shown quite a strong isovector mixing in the elastic and inelastic scattering channels for the neutron rich 38,40S nuclei. In particular, the relative strength of the isovector part of the transition potential required by the inelastic p + 38 S data is significantly stronger than that obtained with the corresponding QRPA transition density.

A proton density bubble in the doubly magic 34Si nucleus

The central densities of protons and neutrons in stable atomic nuclei are saturated. More exotic nuclei — with imbalanced proton and neutron numbers — may have depleted central densities. Experiments now suggest such depletion for the 34Si nucleus.

Density functional theory studies of cluster states in nuclei

The framework of nuclear energy density functionals is applied to a study of the formation and evolution of cluster states in nuclei. The relativistic functional DD-ME2 is used in triaxial and reflection-asymmetric relativistic Hartree-Bogoliubov calculations of relatively light

Two-neutron transfer in nuclei close to the drip line

N=Z

Probing preformedαparticles in the ground state of nuclei

and neutron-rich nuclei. The role of deformation and degeneracy of single-nucleon states in the formation of clusters is analyzed, and interesting cluster structures are predicted in excited configurations of Be, C, O, Ne, Mg, Si, S, Ar, and Ca