Isospin dependence of kinetic energies in light neutron-rich nuclei

Energy spectra andelectric dipole transitions ofN=7 isotones are studied by shell model calculations with isospin dependent kinetic energies for s-d shell orbits. The ground states of¹⁰Li and⁹He are predicted. Electric dipole transitions in¹³C and¹¹Be are studied by using the realistic single-particle wave functions in Woods-Saxon potential.JSPS Fellow for Japanese Junior Scientists.     

Structure of unstable nuclei near proton drip line

Gamov-Teller (GT) states in nuclei near the proton drip line are studied by using a microscopic Hartree-Fock (H-F) + Tamm-Dancoff approximation (TDA) (or random phase approximation (RPA)). The calculations predict that giant Gamow-Teller (GT) β-decays are possible for N=Z nuclei heavier than ₂₈⁵⁶Ni₂₈, carrying most of the sum rule strength. The amplitude of isospin T=1 admixed to the T=0 ground state in N=Z nuclei is also discussed in relation with Fermi β-decay sum rule. Finally, the shapes of unstable nuclei near the proton drip line are studied by using the finite-range droplet model (FRDM).     

Effective nucleon-nucleon forces and interaction of light exotic nuclei with stable nuclei at low energies

The effect of the density dependence of effective nucleon-nucleon forces on the folded potential of the interactions of the light exotic nuclei ⁶He, ¹¹Li, ¹¹Be, and ⁸B with the stable nucleus ¹²C is studied, and the corresponding experimental data on the total reaction cross sections and on elastic scattering are analyzed. A semimicroscopic double-folding model featuring various density-dependent forces based on the M3Y interaction is used together with the nucleon densities as calculated within the density-functional method by using a unified set of parameters for all the above nuclei. It is shown that the angular distributions recently measured for elastic ⁶He scattering on ¹²C at an energy of 41.6 MeV per projectile nucleon and for elastic ¹¹Be scattering on ¹²C at an energy of 49.3 MeV per projectile nucleon can be described satisfactorily if the real part of the optical folded potential is supplemented with a surface term mimicking the contribution of the dynamical polarization potential.     

γ-Spectroscopy of light neutron-rich nuclei after secondary reactions at relativistic energies

After the fragmentation reaction of ⁵⁰Ti on ⁹Be at 330 MeV/u, more than 30 neutron-rich isotopes from B to Ca were selected by the fragment separator FRS at GSI. Peripheral collisions with a secondary Pb target at relativistic energies were used to study the excited states of these isotopes. De-excitation γ-rays were detected with the Darmstadt-Heidelberg Crystal Ball spectrometer. The first results demonstrate the feasibility of in-beam γ-spectroscopy at relativistic energies.     

Inelastic scattering of heavy ions from deformed light nuclei at near-barrier energies

Angular distributions have been measured at energies near the Coulomb barrier for the systems ¹⁸O + ²⁴Mg, ¹²C + ²⁸Si and ^{16, 18}O + ²⁸Si for elastic scattering and inelastic scattering to the first 2⁺ states in ¹⁸O, ²⁴Mg and ²⁸Si. Coupled-channel calculations were required in order to reproduce the details of the strong Coulomb-nuclear interference minima. However, a satisfactory account of the main features of the data was obtained in a first-order DWBA analysis and with the closed formalism of Frahn. With the exception of ¹⁸O, it was sufficient to assume equal charge and optical-potential deformation lengths.     

Binding energies of nuclei

A new theoretical method is proposed to describe known properties of nuclei. The method is based on the theory of nuclear forces given in an earlier paper and results in formulas for the binding energies and dimensions of nuclei which accord with experimental data.     

Structure of light neutron-rich nuclei through coulomb dissociation

Coulomb breakup of neutron-rich nuclei around mass A ∼ 20 has been studied experimentally using secondary beams (∼ 500–600 MeV/u) of unstable nuclei produced at GSI. The spectroscopic factor deduced for the neutron occupying s _1/2 level in ¹⁵C ground state is consistent with the earlier reported value. The data analysis for Coulomb breakup of ¹⁷C shows that most of the cross section yields the ¹⁶C core in its excited state. For ^17–22O, the low-lying E1 strength amounts up to about 12% of the energy weighted dipole sum rule strength depending on neutron excess. The cluster sum rule limit with ¹⁶O as a core is almost exhausted for ^17,18O, while for more neutron rich isotopes the strength with respect to that limit decreases.     

Fusion of light exotic nuclei at near-barrier energies: Effect of inelastic excitation

The effect of inelastic excitation of exotic light projectiles (proton-as well as neutron-rich)¹⁷F and¹¹Be on fusion with heavy target has been studied at near-barrier energies. The calculations have been performed in the coupled channels approach where, in addition to the normal coupling of the ground state of the projectile to the continuum, inelastic excitation of the projectile to the bound excited state and its coupling to the continuum have also been taken into consideration. The inclusion of these additional couplings has been found to have significant effect on the fusion excitation function of neutron-rich¹¹Be on²⁰⁸Pb whereas the effect has been observed to be nominal for the case of proton-rich¹⁷F on the same target. The pronounced effect of the channel coupling on the fusion process in the case of¹¹Be is attributed to its well-developed halo structure.     

Structure study of light unbound nuclei near drip line

Some experimental techniques and theoretical analysis on unbound nuclei structure study are briefly introduced in this article. The unbound nuclei structure investigation can inspect the reliability of theoretical calculation, and is also important to extend the modern nuclear structure model to exotic nuclear regions. With the recent development of radioactive Ion Beam (RIB) facility and some new experimental methods, the structure of unbound nuclei near drip line can be studied in experiment.     

Excitation of two-neutron-halo nuclei in a continuum

Reactions induced by collisions of beams of unstable nuclei with nuclear targets are studied. Kinematically full breakup reactions are considered. A microscopic four-body model of the breakup of two-neutron-halo nuclei is formulated with allowance for special features of their structure. The model relies on the distorted-wave method and creates a basis for the spectroscopy of the continuous spectrum via a consistent analysis of various correlation cross sections.     

Coulomb breakup of light nuclei in the field of a heavy ion at relativistic collision energies

A simple method for calculating the amplitude and the cross section for the Coulomb breakup of a light nucleus into two fragments in the field of a heavy ion at relativistic collision energies is proposed on the basis of time-dependent perturbation theory. It is shown that the resulting amplitude for the process in question has a correct nonrelativistic limit. The contribution of the longitudinal component of the Coulomb field of a heavy ion tends to zero in the ultrarelativistic limit. A specific implementation of the method is demonstrated by taking the example of the Coulomb breakup reaction ²⁰⁸Pb(⁸B, ⁷Bep)²⁰⁸Pb at various collision energies. The results are found to be in agreement with experimental data.     

Full destruction characteristics of light and heavy nuclei with 3.7-158A GeV energies

The full destruction (FD, that implies the disintegration into singly and doubly charged fragments only) characteristics are presented for some light nuclei ( ₆ ¹² C, ₈ ¹⁶ O, ₁₀ ²² Ne, and ₁₄ ²⁸ Si) with an energy of 3.7A GeV and heavy projectiles ₇₉ ¹⁹⁷ Au (10.7A GeV) and ₈₂ ²⁰⁸ Pb (158A GeV) interacting with target nuclei in a photoemulsion. It is shown that (i) the average number of fragments, the realization of various fragmentation channels, and the degree of crushing for light projectiles substantially depend on the charge of a residual nucleus and on the mass of a target nucleus; (ii) the FD probability for residual nuclei with the same charge, as well as the multiplicity of fragments for the same impact parameter of heavy nuclei, are independent of the energy; and (iii) the integral distribution of transverse momenta of doubly charged fragments is described by two exponents (the logarithmic plot exhibits a break).     

Binding energies of even-even superheavy nuclei

The structure of the even-even superheavy nuclei with the proton number Z=98–110 is studied using the self-consistent relativistic mean-field theory. The calculated binding energies are in good agreement with the available experimental ones. An upper limit and a lower limit on the binding energies are set by the calculations. This is useful for future calculations of properties of superheavy nuclei and for the experimental synthesis of superheavy nuclei. The energy surface of some relevant superheavy nuclei is also given and it confirms the correctness of the calculations.     

The continuum strength of single-particle states in nuclei

Methods are devised to calculate the continuum strength of neutron valence orbits starting with an empirical optical-model potential. Allowance is made for the fact that the bound-state and real optical-model potentials have a common nonlocal origin. Direct calculations are made for the $\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, 1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{,}\text{and}\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ orbits of the contribution from the elastic-scattering chann also of the total continuum strength using a spectral representation. As predicted by McKellar and also by an improved perturbation model given here, most of the continuum strength lies in inelastic and rearrangement channels. When combined with 5% missing strength from the NN potential core, the estimated total continuum strength is ?12–15% of the single-particle sum rule, which is compatible with other deductions from experimental data.