Electron scattering form factors for fp-shell nuclei

Elastic and inelastic electron-scattering form factors for multipolarities up to L = 7 and some transition-strength distributions are calculated with shell-model wave functions for about ten target nuclei in the mass range A = 52–62. The results are compared with the available measured transition strengths and (e, e') form factors.     

Electron scattering from transitional nuclei

An electron scattering experiment on ¹⁸⁸Os, ¹⁹⁰Os, ¹⁹²Os, ¹⁹⁴Pt and ¹⁹⁶Pt has been performed at momentum transfers q = 0.6 to 3.2 fm⁻¹. Transition charge densities have been determined for the low-lying 2⁺, 3⁻ and 4⁺ states. The 2⁺ densities are well reproduced within the framework of the interacting boson model 2, where we have determined the boson densities α_ν, α_π, β_νv and β_π. The 4⁺ transition densities could not be reproduced indicating the need for including a g-boson. The ground and transition charge densities of ¹⁸⁸Os, ¹⁹²Os and ¹⁹⁶Pt have been compared with a microscopic calculation. The total binding energies and the intrinsic wave functions have been calculated for different values of β and γ with the constrained triaxial Hartree-Fock-Bogoliubov method using the finite range interaction D1SA. These energies are interpreted as potential energy surfaces and used in the Bohr hamiltonian in order to obtain the total nuclear wave functions. We obtain very good agreement with experiment. The calculated potential energy surfaces show these nuclei to be γ-soft with a shallow minimum for triaxial deformations and rigid in the β direction.     

Continuum effects in the scattering of exotic nuclei

In this work the interaction of the coupled channels DN and ?Ц? _c in an SU(4) extrapolation of the chiral unitary theory, where the ?? _c (2595) resonance appears as dynamically generated from that interaction, is extended to produce results in finite volume. Energy levels in the finite box are evaluated and, assuming that they would correspond to lattice results, the inverse problem of determining the phase shifts in the infinite volume from the lattice results is solved. We observe that it is possible to obtain accurate ?Ц? _c phase shifts and the position of the ?? _c (2595) resonance, but it requires the explicit consideration of the two coupled channels. We also observe that some of the energy levels in the box are attached to the closed DN channel, such that their use to induce the ?Ц? _c phase shifts via Lüscher's formula leads to incorrect results.     

Shell model results for exotic nuclei

Recent developments of the nuclear shell model are presented. The magic numbers are the key concept of the shell model, and are shown to be different in exotic nuclei from those of stable nuclei. Their novel origin and robustness will be discussed. By the Monte Carlo Shell Model (MCSM), the structure of low-lying states can be studied with realistic interactions for a wide variety of nuclei. Some examples are discussed in connection to the triaxial deformation and a narrow shell gap at N = 20 for Z smaller.Received: 10 January 2003, Published online: 9 March 2004PACS: 21.60.Cs Shell model - 21.30.Fe Forces in hadronic systems and effective interactions - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 21.10.-k Properties of nuclei; nuclear energy levels     

Breakup reaction models for exotic nuclei

Breakup reactions are one of the main tools for the study of exotic nuclei. In particular, Coulomb breakup is expected to provide information on spectroscopic properties of halo nuclei and on astrophysical S factors for radiative-capture reactions. The simplest studies are based on perturbation theory and especially on its first order. However the validity of the first-order approximation may be limited for extended systems such as halo nuclei and its conditions are not always satisfied in existing experiments. More elaborate reaction models are available: resolution of the semi-classical time-dependent Schr?dinger equation, eikonal and dynamical eikonal approximations, method of coupled discretized-continuum channels, adiabatic approximation. These methods are reviewed, summarized and illustrated. Their interest and limitations are discussed.     

Very neutron-rich exotic nuclei

A brief summary is done of the various types of experiment used in studies of the very neutron rich nuclei. Some highlights are given for the two-neutron halo and¹¹Li nucleus and for the one-neutron halo and¹¹Be nucleus.     

Symmetry in exotic nuclei

Symmetries have played an important role in the elucidation of the structure of nuclei and will continue to do so for exotic nuclei. As an example, an application of pseudo-SU(4) symmetry is discussed. It can be used as a starting point for a boson model that includes T = 0 as well as T = 1 bosons (IBM-4); applications are presented for N = Z nuclei from ⁵⁸Cu to ⁷⁰Br. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: isacker@ganil.fr     

Large-scale shell model calculations for exotic nuclei

Recent shell model calculations for the neutron-rich nuclei around the magic numbers N = 20, N = 28 and N = 40 are reviewed. We stress two points: i) The crucial role played by the monopole part of the effective interaction that determines the evolution of the spherical mean field. In particular, the reduction in the quasiparticle gaps at the magic numbers can erode or even erase the shell closures. ii) The rich variety of structures that can be found in these situations, with coexisting deformed and spherical states, rapid changes of behaviour with N or Z, and the massive occurrence of intruder states as ground states. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: alfredo.poves@uam.es     

Electron scattering on two-neutron halo nuclei: The case of He

The formalism to describe electron scattering reactions on two-neutron halo nuclei is developed. The halo nucleus is described as a three-body system (core +n + n), and the wave function is obtained by solving the Faddeev equations in coordinate space. We discuss elastic and quasielastic scattering using the impulse approximation to describe the reaction mechanism. We apply the method to investigate the case of electron scattering on ⁶He. Spectral functions, response functions, and differential cross sections are calculated for both neutron knockout and knockout by the electron.     

Detecting bubbles in exotic nuclei

The occurrence of a bubble, due to an inversion of s_1/2 state with the state usually located above, is investigated. Proton bubbles in neutron-rich argon isotopes are optimal candidates. Pairing effects which can play against the bubble formation are evaluated. They cannot prevent bubble formation in very neutron-rich argon isotopes such as ⁶⁸Ar. This pleads for a measurement of the charge density of neutron-rich argon isotopes in the forthcoming years, with the advent of electron scattering experiments in next generation exotic beam facilities such as FAIR or RIBF.     

Reaction mechanisms with exotic nuclei

This article examines a number of reaction mechanisms for scattering initiated by an exotic projectile. Comparisons are made with recent experimental data, in order to extract information on the peculiarity of the nuclear structure under extreme conditions and to test the accuracy of the available theoretical methods. Predictions for future experiments are also made.     

Reaction dynamics with exotic nuclei

We review the new possibilities offered by the reaction dynamics of asymmetric heavy-ion collisions, using stable and unstable beams. We show that it represents a rather unique tool to probe regions of highly asymmetric nuclear matter (ANM) in compressed as well as dilute phases, and to test the in-medium isovector interaction for high-momentum nucleons. The focus is on a detailed study of the symmetry term of the nuclear equation of state (EOS) in regions far away from saturation conditions but always under laboratory controlled conditions.

Thermodynamic properties of ANM are surveyed starting from non-relativistic and relativistic effective interactions. In the relativistic case, the role of the isovector–scalar δ-meson is stressed. The qualitative new features of the liquid–gas phase transition, “diffusive” instability and isospin distillation, are discussed. The results of ab initio simulations of n-rich, n-poor, heavy-ion collisions, using stochastic isospin-dependent transport equations, are analyzed as a function of beam energy and centrality. The isospin dynamics plays an important role in all steps of the reaction, from prompt nucleon emissions to the final fragments. The isospin diffusion is also of large interest, due to the interplay of asymmetry and density gradients. In relativistic collisions, the possibility of a direct study of the covariant structure of the effective nucleon interaction is shown. Results are discussed for particle production, collective flows and isotransparency.

Perspectives of further developments of the field, in theory as well as in experiment, are presented.     

丰中子奇异核17B的实验研究

在兰州重离子加速器国家实验室(HIRFL)放射性次级束流线(RIBLL)上,用束流透射法测量了丰中子奇异核17B与C靶反应的总截面.假定17B具有15B(核芯) 2n结构,采用Gauss HO形式的密度分布和零力程Glauber模型进行计算的结果可以很好地拟合实验数据,并得出17B的密度分布有一个很大的弥散,表明17B是双中子晕核.     

The ISOLDE laser ion source for exotic nuclei

At the ISOLDE on line mass separator a system of copper vapor lasers and dye lasers serves for resonant ionization of atoms inside a hot cavity attached to the target. Radioactive ion beams of Yb, Ag, Mn, Ni, Zn, Be, Cu, Cd and Sn were produced with the Resonance Ionization Laser Ion Source (RILIS). Two and three step excitation schemes are used, providing an ionization efficiency of about 10%. Thanks to the use of the RILIS it became possible to ionize beryllium efficiently at ISOLDE, and all particle stable Be isotopes could be separated for the first time. Separation of Ag and Cu nuclear isomers was achieved in the ion source by appropriate tuning of the laser wavelength. New isotopes of Ag, Mn, Zn, Cd and Sn were found, including the r process “waiting point” nucleus ¹²⁹Ag. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electron scattering on two-neutron halo nuclei: The case of 6He

The formalism to describe electron scattering reactions on two-neutron halo nuclei is developed. The halo nucleus is described as a three-body system (core +n + n), and the wave function is obtained by solving the Faddeev equations in coordinate space. We discuss elastic and quasielastic scattering using the impulse approximation to describe the reaction mechanism. We apply the method to investigate the case of electron scattering on ⁶He. Spectral functions, response functions, and differential cross sections are calculated for both neutron knockout and α knockout by the electron.