Low densities in nuclear and neutron matters and in the nuclear surface

Abstract

Abstract. Nuclear and neutron matters are investigated in the low density region, well below the nuclear saturation density. Microscopic calculations, based on the Bethe-Brueckner approach with a few realistic nucleon-nucleon potentials, are compared with the predictions of a set of phenomenological effective interactions, mostly employed in nuclear structure studies. An energy functional is constructed on the basis of the microscopic bulk EoS and applied to a selection of nuclei throughout the mass table. The results provide a microscopic basis for a link between nuclear surface behaviour and neutron EoS previously observed with phenomenological effective forces. Possible effects of pairing on asymmetric nuclear matter are also analyzed in detail. The results are expected to illuminate the physical mechanisms which determine the behaviour of the surface density tail in exotic nuclei.

Neutron skin thickness in the droplet model with surface width dependence: Indications of softness of the nuclear symmetry energy

“…Experimentalists combine two different techniques in this case [48][49][50], namely the measurement of the antiprotonic x rays that determine the atomic level shifts and widths due to the strong interaction and the radiochemical analysis of the yields after the antiproton annihilation. The values of the neutron skin thickness of 26 stable nuclei from 40 Ca to 238 U deduced from antiprotonic atoms data by Trzcińska et al [48,49] follow a roughly linear trend with the overall relative neutron excess I = (N − Z)/A of these nuclei. This trend can be fitted by the relationship R np = (0.90 ± 0.15)I + (−0.03 ± 0.02) fm as discussed in Refs.…”

“…We also know that R np in 208 Pb shows a linear dependence with these slopes at some subsaturation density ρ 0.10 fm −3 [37][38][39][40]. Therefore it is reasonable that the neutron skin thickness in 208 Pb and the leading term L/3ρ 0 of Eqs.…”

“…These facts, and the noticed correlation between L and J /Q, allow one to interpret in a qualitative way within the DM, the correlation pointed out in Refs. [37][38][39][40] between the slope of the symmetry energy at some subsaturation density ρ 0.10 fm −3 and the neutron skin thickness in a heavy nucleus. In a recent work [51] we have investigated further the relations of the neutron skin thickness with the parameters L and K sym that characterize the density dependence of the symmetry energy around saturation.…”

“…It has been shown that the neutron skin thickness in heavy nuclei, like 208 Pb, calculated in mean-field models with either nonrelativistic or relativistic effective nuclear interactions, displays a linear correlation with the slope of the neutron equation of state (EOS) obtained with the same interactions at a neutron density ρ ≈ 0.10 fm −3 [37][38][39]. A similar correlation exists between R np and the density derivative of the bulk symmetry energy [13][14][15][16]33,40,41], as the latter is a measure of the pressure difference between neutrons and protons. These correlations have been exploited in recent years to gain a deeper understanding of the isospin properties of the effective nuclear interaction and to relate them with nuclear and astrophysical observations.…”

Neutron matter at low density and the unitary limit

“…Despite that BBG is essentially a low density expansion, it has been found [13,14] that the convergence is valid up to densities as high as few times saturation density in symmetric nuclear matter and even better in neutron matter.…”