Neutron star structure and the neutron radius of 208Pb.

We study relationships between the neutron-rich skin of a heavy nucleus and the properties of neutron-star crusts. Relativistic effective field theories with a thicker neutron skin in 208Pb have a larger electron fraction and a lower liquid-to-solid transition density for neutron-rich matter. These properties are determined by the density dependence of the symmetry energy which we vary by adding nonlinear couplings between isoscalar and isovector mesons. An accurate measurement of the neutron radius in 208Pb-via parity violating electron scattering-may have important implications for the structure of the crust of neutron stars.     

Theoretical study on neutron distribution of ~(208)Pb by parity-violating electron scattering

The precise determination of neutron distribution has important implications for both nuclear structure and nuclear astrophysics. The purpose of this paper is to study the characteristics of neutron distribution of~(208) Pb by parity-violating electron scattering(PVS). Parity-violating asymmetries of~(208) Pb with different types of neutron skins are systematically calculated and compared with the experimental data of PREx. The results indicate that the PVS experiments are very sensitive to the nuclear neutron distributions. From further PVS measurements, detailed information on nuclear neutron distributions can be extracted.     

Determination of the neutron scattering length of208Pb by the neutron interferometry method

The coherent scattering length of²⁰⁸Pb was measured by means of the neutron interferometry method and the value ofb _c =9.494(29) fm was obtained.     

Nature of parity violation in neutron interaction with lead

The effect of parity violation in the interaction of thermal neutrons with lead was discovered in a number of studies. According to the existing theory, this effect is explained by the mixing of compound states characterized by different parities (s-and p-wave resonances). In view of the absence of a p-wave resonance in the region of thermal neutron energies, it is of importance to reveal a level below the neutron binding energy, a so-called negative resonance. The energy dependence of the cross section for radiative neutron capture on lead was measured in the present study, and it is shown that, for the ²⁰⁷Pb isotope, the results of this measurement deviate from the \({1 \mathord{\left/ {\vphantom {1 {\sqrt E }}} \right. \kern-\nulldelimiterspace} {\sqrt E }}\) law, thereby suggesting the presence of a strong negative resonance. The parameters of this resonance are estimated.     

Parity violation in electron scattering

By comparing the cross sections for left- and right-handed electrons scattered from various unpolarized nuclear targets, the small parity-violating asymmetry can be measured. These asymmetry data probe a wide variety of important topics, including searches for new fundamental interactions and important features of nuclear structure that cannot be studied with other probes. A special feature of these experiments is that the results are interpreted with remarkably few theoretical uncertainties, which justifies pushing the experiments to the highest possible precision. To measure the small asymmetries accurately, a number of novel experimental techniques have been developed.     

Parity violation in electron scattering

Approximations based on the 2PI effective action are used to investigate the process of equilibration in ϕ⁴ theory in 3+1 dimensions, both in the symmetric and broken phase. A special emphasis is put on the study of the kinetic and chemical equilibration.     

Neutron scattering from 208Pb

Elastic scattering of 7, 9, 11, 20 and 26 MeV neutrons from ²⁰⁸Pb has been measured with the Ohio University Tandem Van de Graaff accelerator. Standard pulsed beam time-of-flight techniques were employed. Measurements of the incident flux at 0° were used to normalize the differential cross sections. The measured cross sections were corrected for dead time, detector efficiency, flux attenuation, multiple scattering, finite geometry, neutron source anisotropy and compound elastic contribution. Relative uncertainties are estimated to be between 5%–10% and the uncertainty in the normalization is estimated to be less than 5 %. The data were used to obtain neutron optical potential parameters. A comparison with proton optical parameters is presented, and the (p, n) quasi-elastic cross section is calculated and compared with available data. Deformation parameters for the 3^? state (Q = ?2.615 MeV) and 5ā (Q = ?3.198 MeV) in ²⁰⁸Pb were obtained at incident energies of 11 and 26 MeV.     

Compton scattering on208Pb

In this paper we briefly review the formalism of the nuclear Compton scattering in the frame of the low-energy theorems (LET). We treat the resonant terms of the amplitude, having collective intermediate nuclear states, as a superposition of Lorentz lines with energy, width and strength fixed by the photo-absorption experiments. The gauge terms are evaluated starting from a simple, but realistic, nuclear Hamiltonian. Dynamical nucleon-nucleon correlations are consistently taken into account, beyond those imposed by the Pauli principle. The comparison of the theoretical predictions with the data of elastic diffusion of photons from²⁰⁸Pb shows that LET are insufficient to account for the experiment.     

Parity violation,the neutron radius of lead,and neutron stars

The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties in the reaction mechanism. The parity radius experiment at the Jefferson Laboratory offers an attractive electro-weak alternative to the hadronic program and promises to measure the neutron radius of ²⁰⁸Pb accurately and model independently via parity-violating electron scattering. In this contribution we examine the far-reaching implications that such a determination will have in areas as diverse as nuclear structure, atomic parity violation, and astrophysics.     

Scaling violation in quasielastic electron scattering

The scaling law in quasielastic electron scattering is broken due to exchange forces. The violation in the longitudinal response function is attributed to the central part of exchange forces, while in the transverse response the tensor part also leads to the breaking. The effects of one-boson exchange potentials are discussed.     

Parity violation in neutron scattering on lead isotopes

On the basis of an analysis of experimental data, it is shown that a subthreshold (negative) p-wave resonance can exist in the ²⁰⁴Pb isotope at E _p =?16 eV. The presence of this resonance may explain unexpectedly large values observed experimentally for the P-odd angle of the rotation of the spin of transversely polarized neutrons about their momentum that are scattered on a natural mixture of lead isotopes. No available data are at odds with the existence of the E _p =?16 eV subthreshold resonance in ²⁰⁴Pb.     

Parity violation in polarised electron deuteron scattering

Preliminary calculations show that the parity violating asymmetry in polarised electron deuteron elastic scattering can be as large as observed in the SLAC experiment even in the intermediate energy region. We propose that experiments should be done to search for these asymmetries.     

Evidence of parity violation in neutron capture by 117Sn

An asymmetry measurement in the radiative capture of polarized cold neutrons in the raction ¹¹⁷Sn(n, γ) ¹¹⁸Sn is reported. The result a = (4.4 ± 0.6) × 10^?4 gives a clear evidence of a parity non-conserving effect.     

Potentials for heavy ions scattering from 208Pb

Data for the elastic scattering of ¹²C(96 MeV), ¹⁶O(129.5 and 192 MeV) and ²⁰Ne (161.2 MeV) from ²⁰⁸Pb have been used to deduce properties of the ion-ion potential. In particular, the strength of the absorptive potential in the surface region was found to be comparable to that of the real potential. The importance of small-angle data is emphasized.     

Low-lying normal parity excitations in the 208Pb(p,p')208Pb reaction at Ep = 61.2 MeV

Differential cross sections for the excitation of the 3₁^?, 5₁^?, 5₂^?, 7₁^?, 2₁⁺, 4₁⁺, 6₁⁺ levels in ²⁰⁸Pb by 61.2 MeV protons have been measured. The results of collective-model and microscopic-model calculations are compared with the data. A “realistic” two-body interaction is used in the microscopic calculations. Transition densities obtained from electron scattering data and particle-hole wave functions are both considered. The results obtained using the electron scattering transition densities are quite good and provide an indication that ?_n ≧ ?_p for these excitations. The results obtained using the theoretical transition densities give only qualitative reproduction of the data. Finally, some discrepancies in earlier analyses of ²⁰⁸Pb+p data are resolved.