Neutron density distributions deduced from antiprotonic atoms

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results.     

Nucleon charge radius from QCD sum rules

The proton and neutron electric radii are calculated within QCD using the sum rules method for processes with small momentum transfers. The agreement with experimental values is good for the proton radius and somewhat poorer for the neutron one due to the numerical smallness.     

Measurement of the neutron radius of 208Pb through parity violation in electron scattering

We report the first measurement of the parity-violating asymmetry A(PV) in the elastic scattering of polarized electrons from 208Pb. A(PV) is sensitive to the radius of the neutron distribution (R(n)). The result A(PV)=0.656±0.060(stat)±0.014(syst) ppm corresponds to a difference between the radii of the neutron and proton distributions R(n)-R(p)=0.33(-0.18)(+0.16) fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.     

Calculation of nucleon densities in calcium,nickel, and molybdenum isotopes on the basis of the dispersive optical model

The radial distributions of proton and neutron densities in the even–even isotopes ^40?70Cа and ^48?78Ni and the analogous distributions of neutron densities in the even–even isotopes ^92?138Mo were calculated on the basis of the mean-fieldmodel involving a dispersive optical potential. The respective root-mean-square radii and neutron-skin thicknesses were determined for the nuclei under study. In N > 40 calcium isotopes, the calculated neutron root-mean-square radius exhibits a fast growth with increasing N, and this is consistent with the prediction of the neutron-halo structure in calcium isotopes near the neutron drip line.     

应用原子核的宏观－微观模型研究远离稳定线核的性质

应用原子核的宏观－微观模型研究远离稳定线核的性质，得到了一些结果，例如质子和中子滴线，质子和中子密度分布及其均方根半径和中子皮厚度随同位素位移的变化．对一些奇异核性质的计算结果同相对论平均场方法计算的结果作了比较，对质子滴线附近核的质子放射性也作了简要讨论．     

Neutron radii and skins in the Hartree-Fock-Bogoliubov calculations

We examine the systematic predictions for proton and neutron radii in even-even nuclei made by the self-consistent Skyrme-Hartree-Fock-Bogoliubov theory. Such an approach allows us to describe nuclei far from stability, where the spatial extensions of a nuclear system crucially depend on the continuum effects. We concentrate on the influence of spherical shell structure on global behavior of radii. The (N, Z)-localization of neutron and proton skins is discussed.     

The neutron distribution in nuclei from bremsstrahlung-weighted cross-sections

Bremsstrahlung-weighted cross-section (bwcs) measurements may be a decisive step to obtain information about the difference between neutron and proton radii. A model-independent relation is discussed between the total bwcs, the relative intensity of the bwcs of the upper (T_>) fragment of the dipole excitation and the neutron and proton radii.     

Nuclear and neutron star radii

We investigate the correlation between nuclear neutron radii and the radius of neutron stars. We use a well-established hadronic SU(3) model based on chiral symmetry that naturally includes nonlinear vector meson and scalar meson–vector meson couplings. The relative strengths of the couplings modify the nuclear isospin-dependent interactions. We study the dependence of nuclear and neutron star radii on the coupling strengths. The relevance of the results for parity-violating electron–nucleus scattering is discussed.     

Nuclear periphery studied with antiprotonic atoms

Two experimental methods were employed to study the nuclear peripheral density. The first method was based on antiprotonic X ray measurements. The widths and shifts of the last atomic state levels available for the antiproton were deduced from the shape of the X-ray lines. These observables are sensitive to the nuclear matter density at a distance 1.5 fm larger than the charge half-density radius. The other method consisted in studying the antiproton annihilation products and gave information on the neutron-to-proton density ratio at a radius 2.5 fm larger than the charge half-density radius. This article presents the results obtained by the PS209 collaboration in measurements performed with the LEAR facility at CERN. Neutron densities and differences of neutron and proton root-mean-square radii were deduced for isotopes over a wide mass range (A = 40–238).     

A potential diquark in the proton

A non-relativistic, QCD-based, potential quark model for the proton and the neutron inevitably predicts a spin-0 diquark structure with an rms radius of the order of 0.35 fm or smaller. We prove this by solving the (S wave}) hamiltonian by De Rüjula et al. with variational methods. It is essential to include all quark interactions and to use realistic test wave–functions. The protondelta mass difference, the magnetic moments and the nucleon charge radii can be reproduced only with wave functions that contain a mixture of quark–diquark and three–quark states. Approaches with just a quark–diquark component give incorrect magnetic moments, while those without diquarks lead to a too low proton–delta mass difference.     

Some characteristics of nuclear densities

We propose a simple expression for nuclear densities, which brings out the following important nuclear properties: (i) shell effects in proton and neutron central densities, (ii) approximate global constancy of neutron central densities, (iii) approximate constancy ofRN ^?1/3 and R_pZ^?1/3 whereR is the nuclear half-density radius andR _p is the rms radius of the proton density, (iv) larger surface thickness and rms radius for neutron density as compared to those for proton density.     

Proton and neutron radii of208Pb from transfer reactions and single particle energies

Neutron and proton transfer cross sections and single-particle energies are converted into rms radii of density distributions via independent particle wave functions. The radii of the neutron excess and the analogous “proton excess” are found to be the same. Comparison is made with the results of other experiments.     

Magnetic moment and radius of the nucleon in a nonlocal model of meson-nucleon interaction

Magnetic moment and radius of the nucleon are calculated in a nonlocal extension of the chiral linear σ-model. Properties of the nonlocal model under the vector and axial transformations are considered. The conserved electromagnetic and vector currents, and partially conserved axial vector current are obtained. In the calculation of the nucleon electromagnetic vertex the π- and σ-loop diagrams are included. Contribution from vector mesons is added in the vector meson dominance model with a gauge-invariant photon-meson coupling. The nonlocality parameter associated with the πN interaction is fixed from the experimental magnetic moment of the neutron. Other parameters (nonlocality parameter for the σN interaction and the mass of the σ-meson) are constrained by the magnetic moment of the proton. The calculated electric and magnetic mean-square radii of the proton and neutron are in satisfactory agreement with experiment. Received: 12 February 2001 / Accepted: 4 September 2001     

Isospin dependence of proton and neutron radii within relativistic mean field theory

The proton and neutron radii of even-even β-stable nuclei with A ⩾ 40 and a few chains of isotopes with Z = 50, 56, 82, 94 protons and isotones with N = 50, 82, 126 neutrons are analyzed. The average isospin dependence of the radii evaluated within the relativistic mean field theory is studied. A simple, phenomenological formula for neutron radii is proposed.     

Thick skin in neutron/proton-rich sodium isotopes

Nucleon (both neutron and proton) density distributions of the chain of sodium isotopes are calculated using a semi-phenomenological model of nuclear density which incorporates correctly the asymptotic behaviour and the behaviour near the centre. The experimental charge root-mean-square radii and the single neutron and proton separation energies, required as input, are used. The calculated interaction cross-sections using these densities in the Glauber model agree well with the experiment. The calculated neutron rms radii r _n and the nuclear skin thickness ( r _n - r _p) closely agree with the corresponding experimental values and also are consistent with the Relativistic Hartree-Bogoliubov (RHB) calculations. Received: 24 April 2001 / Accepted: 28 June 2001     

Charge and mass radii of the tin isotopes

Data on the isotope shift of the nuclear charge densities of the tin isotopes and of their mean square charge radii are considered from the viewpoint of the Hartree-Fock and Droplet Models. Attention is paid to the electromagnetic corrections of order 1/m². Through a leptodermous analysis of charge and matter densities we find: (i) differences of m.s. charge radii are mainly sensitive to the external region, (ii) the electromagnetic corrections are important in that region, (iii) despite different leptodermous properties, forces Ska and GO-P lead to the same neutron skin thickness. The average rate of variation of the proton m.s. radius is interpreted as favouring either a low valueQ≈30 MeV for the droplet model asymmetry parameter, or a zero value for the saturation asymmetry parameterL.     

Nuclear properties far from the stability line in the relativistic mean field theory

We study the nuclear properties far from the stability line in the relativistic mean field theory. We find that the parameter set NL 1 provides very good results on binding energies of unstable nuclei, while NL2 results are not good, although both parameter sets give equally good results on nuclear properties for stable nuclei. We discuss the neutron number dependence of the proton and the neutron root mean square radii of proton magic nuclei.     

Study of Electric Polarizabilities of Nucleon with a Constituent Quark Model and Pion Meson Cloud

In this work, a subtle role of the pion meson cloud effect on the electric polarizabilities of the proton and neutron is stressed. It is shown that the electric polarizabilities of the proton and neutron, and the difference between the electric polarizabilities of the proton and neutron can be explained by including the pion meson cloud explicitly. However, the magnitude of the estimated mean-square charge radius of the neutron is still far from the measurement.     

Criterion for a unique non-relativistic quark model

We have calculated the mean square charge radii of the neutron and proton, and compared them with the experimental values, to construct a unique non-relativistic quark potential model. It is shown for the first time that, contrary to general belief, it is possible to reproduce simultaneously the baryon mass spectrum and the electromagnetic sizes of neutron and proton using a single potential model. It was found necessary to add admixtures of excited states of the nucleon in the unperturbed ground state wavefunctions.     

Neutron skin effect of some Mo isotopes in pre-equilibrium reactions

The neutron skin effect has been investigated for even isotopes of molybdenum at 25.6 MeV ^{94 − 100}Mo(p, xn) reaction using the geometry-dependent hybrid model of pre-equilibrium nuclear reactions. Here the initial neutron/proton exciton numbers were calculated from the neutron/ proton densities obtained from an effective nucleon–nucleon interaction of the Skyrme type. Initial exciton numbers from different radii of even Mo isotopes were used to obtain the corresponding neutron emission spectra. In this investigation the calculated results are compared with the experimental data as also with each other. The results using central densities in the geometry-dependent hybrid model are in better agreement with the experimental data.