Isotopic dependence of the giant monopole resonance in the even-A 112-124Sn isotopes and the asymmetry term in nuclear incompressibility

A Statistical Approach to Neutron Stars' Crust-Core Transition Density and Pressure

In this paper, a regression model between neutron star crust-core pressure and the symmetry energy characteristics was estimated using the Akaike information criterion and the adjusted coefficient of determination Radj2. The most probable value of the transition density, which should characterize the crust-core environment of the sought physical neutron star model, was determined based on the obtained regression function. An anti-correlation was found between this transition density and the main characteristic of the symmetry energy, i.e., its slope L.

Toward a Unified Description of Isoscalar Giant Monopole Resonances in a Self-Consistent Quasiparticle-Vibration Coupling Approach

The nuclear incompressibility is a key parameter of the nuclear equation of state that can be extracted from the measurements of the so-called "breathing mode" of finite nuclei. The most serious discrepancy so far is between values extracted from Pb and Sn, that has provoked the longstanding question "Why is tin so soft?". To solve this puzzle, a fully self-consistent quasiparticle random-phase approximation plus quasiparticle-vibration coupling approach based on Skyrme-Hartree-Fock-Bogoliubov is developed. We show that the many-body correlations introduced by quasiparticle-vibration coupling, which shift the isoscalar giant monopole resonance energy in Sn isotopes by about 0.4 MeV more than the energy in ^{208}Pb, play a crucial role in providing a unified description of the isoscalar giant monopole resonance in Sn and Pb isotopes. The best description of the experimental strength functions is given by SV-K226 and KDE0, which are characterized by incompressibility values K_{∞}=226  MeV and 229 MeV, respectively, at mean field level.

Dynamic Isovector Reorientation of Deuteron as a Probe to Nuclear Symmetry Energy

We present the calculations on a novel reorientation effect of deuteron attributed to isovector interaction in the nuclear field of heavy target nuclei. The correlation angle determined by the relative momentum vector of the proton and the neutron originating from the breakup deuteron, which is experimentally detectable, exhibits significant dependence on the isovector nuclear potential but is robust against the variation of the isoscaler sector. In terms of sensitivity and cleanness, the breakup reactions induced by the polarized deuteron beam at about 100 MeV/u provide a more stringent constraint to the symmetry energy at subsaturation densities.

Measurement of the isoscalar monopole response in the neutron-rich nucleus 68Ni

The isoscalar monopole response has been measured in the unstable nucleus (68)Ni using inelastic alpha scattering at 50A  MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1 ± 1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9 ± 1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L = 0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L=0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.

Has a thick neutron skin in 208Pb been ruled out?

The Lead Radius Experiment has provided the first model-independent evidence in favor of a neutron-rich skin in 208Pb. Although the error bars are large, the reported large central value of 0.33 fm is particularly intriguing. To test whether such a thick neutron skin in 208Pb is already incompatible with laboratory experiments or astrophysical observations, we employ relativistic models with neutron-skin thickness in 208Pb ranging from 0.16 to 0.33 fm to compute ground-state properties of finite nuclei, their collective monopole and dipole response, and mass-versus-radius relations for neutron stars. No compelling reason was found to rule out models with large neutron skins in 208Pb from the set of observables considered in this Letter.

Constraining the nuclear equation of state at subsaturation densities

Only one-third of the nucleons in 208Pb occupy the saturation density area. Consequently, nuclear observables related to the average properties of nuclei, such as masses or radii, constrain the equation of state not at the saturation density but rather around the so-called crossing density, localized close to the mean value of the density of nuclei: ρ is approximately equal to 0.11 fm(-3). This provides an explanation for the empirical fact that several equation of state quantities calculated with various functionals cross at a density significantly lower than the saturation one. The third derivative M of the energy per unit of volume at the crossing density is constrained by the giant monopole resonance measurements in an isotopic chain rather than the incompressibility at saturation density. The giant monopole resonance measurements provide M=1100±70 MeV (6% uncertainty), whose extrapolation gives K(∞)=230±40 MeV (17% uncertainty).

Nuclear symmetry energy probed by neutron skin thickness of nuclei

We describe a relation between the symmetry energy coefficients c(sym)(rho) of nuclear matter and a(sym)(A) of finite nuclei that accommodates other correlations of nuclear properties with the low-density behavior of c(sym)(rho). Here, we take advantage of this relation to explore the prospects for constraining c(sym)(rho) of systematic measurements of neutron skin sizes across the mass table, using as example present data from antiprotonic atoms. The found constraints from neutron skins are in harmony with the recent determinations from reactions and giant resonances.

First measurement of the giant monopole and quadrupole resonances in a short-lived nucleus: 56Ni

The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the 56Ni unstable nucleus by inducing the 56Ni(d,d') reaction at 50A MeV in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at 19.3+/-0.5 MeV and 16.2+/-0.5 MeV, respectively. The corresponding angular distributions are extracted from 3 degrees to 7 degrees . A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energy-weighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediate-energy radioactive beam facilities.