Neutron halos in the excited states for N=127 isotones

Properties of the ground states and the excited states of N=127 isotones are investigated by using the nonlinear relativistic mean field theory with the interactions PK1. By analyzing the rms of proton and neutron, the single particle energies of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in ²⁰⁹Pb. It is also predicted that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in ²⁰⁷Hg, ²⁰⁸Tl, ²¹⁰Bi and ²¹¹Po.     

Neutron halos in the excited states for N=127 isotones

Properties of the ground states and the excited states of N=127 isotones are investigated by using the nonlinear relativistic mean field theory with the interactions PK1. By analyzing the rms of proton and neutron, the single particle energies of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 209Pb. It is also predicted that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 207Hg, 208Tl, 210Bi and 211Po.     

A relativistic continuum Hartree-Bogoliubov theory description of N=3 isotones

The ground-state properties of N=3 isotones and mirror nuclei have been investigated in the Rrelativistic Continuum Hartree-Bogoliubov theory with the NLSH effective interaction. Pairing correlations are taken into account by a density-dependent δ-force. The calculations show that the proton density distributions of ⁸B and ⁹C have a long tail, the core has an increasing tendency of ⁹C and the paired off valence protons make the halo distribution shrink. The cross sections for the ⁸B(⁹C)+¹²C reaction which are consistent with the experimental data are calculated using the Glauber model. On the whole, we think that ⁸B is a one-proton halo nucleus and ⁹C is a two-proton halo nucleus.     

Yrast bands in N = 91 isotones

The in-beam spectroscopy on N = 91 isotones has been carried out using the ¹²C + ¹⁵⁰Nd reaction. The νi _13/2 and νh _11/2 bands of ¹⁵³Sm have been extended up to 33/2⁺ and 31/2^-, respectively. Two new γ-rays have been located on the top of the unfavored band with νi _13/2 configuration in ¹⁵⁷Dy. Two identical relationships have been established in the low-spin region of the yrast νi _13/2 configuration between ¹⁵³Sm and ¹⁵⁵Gd, and between unfavored bands of ¹⁵⁵Gd and ¹⁵⁷Dy. Here all these nuclei have the same neutron number N = 91. Received: 28 June 2000 / Accepted: 20 October 2000     

On the structure of N=126 isotones

TheN=126 isotones with 208 ≦A ≦ 215 have been studied with the shell-model including configuration mixing. Two different interactions have been employed: the schematic surface delta interaction and the realistic Kuo-Herling interaction. The energy spectra,B(E2)-values andg-factors are well reproduced with effective operators. Calculations on theg-factors of²⁰⁹Bi in a more extended model space show that the anomalous spin contribution to the dipole moment cannot be attributed fully to one-particle-one-hole excitations.     

Microscopic description of collective states near the yrast line of nuclei with stable octupole deformation

Collective states near the yrast line in nuclei with stable octupole deformation are discussed in the framework of the random phase approximation (RPA) based on the cranking model. These vibrational states are characterized by the quantum number of generalized signature (eigenvalue of the operator S_x = PR_x^?1(π)). In the zero-octupole deformation limit the RPA equations of motion are reduced to the well-known ones characterized by both values of parity and signature, respectively. The connection of the translational and rotational symmetry of the model hamiltonian with the spurious solutions of the RPA equation of motion is discussed. Expressions for the reduced probabilities B(E1), B(E2) and B(E3) are obtained. These expressions confirm the conclusions of phenomenological models for the strong E1 and E3 intraband transitions in nuclei with stable octupole deformation.     

New high-spin states of 147Nd and 145Ce: Octupole correlation in the N = 87 isotones

High-spin states of the N = 87 nuclei, ¹⁴⁷Nd and ¹⁴⁵Ce, have been populated in the ¹²C + ²³⁸U and ¹⁸O + ²⁰⁸Pb fusion-fission reactions at 90 MeV and 85 MeV bombarding energy, respectively. The emitted γ-radiation was detected using the Euroball III and IV arrays. High-spin states of the ¹⁴⁷Nd isotope have been identified for the first time. The high-spin yrast and near-to-yrast structures of the ¹⁴⁵Ce nucleus have been considerably extended. The newly observed structures, discussed by analogy with the neighbouring isotones, show the coupling of an h_9/2 neutron to the quadrupole and octupole excitations of the core.     

Microscopic description of collective motion in pf shell nuclei

Rotational and vibrational excitations in pf shell nuclei are studied by means of the generator coordinate method. The generator coordinates are the pairing energies and the quadrupole moments of constrained Hartree-Bogoliubov states, projected onto good angular momenta and particle numbers. The Kuo interaction and the one modified by McGrory are used. The vibrational character of the yrast energies appears to be produced by mixing prolate and oblate wave functions. Pairing correlations are essential for this mixing. In contrast to the yrast states the excitation energies of the higher states depend strongly on the interaction used. They show good agreement with experiment, particularly in the case of ⁴⁸Ti with the Kuo force. The calculated B(E2) values exhibit a rotational band structure in general, even if the energies look more vibrational. The force dependence of the excitation energies can qualitatively be understood by inspection of the intrinsic energy surface.     

Microscopic calculation of IBM parameters by using intrinsic states

The overlaps between intrinsic fermionic and bosonic wave functions are required to be the same. This provides relations between fermion and boson variables. These relations are used in conjunction with an OAI procedure for intrinsic states to map the shell-model space operators onto their equivalent boson space operators. As an example, a QQ interaction is mapped.     

Level inversion of N=9 isotones in the relativistic mean-field theory

We have studied the ground state properties of N=8 and N=9 isotones in the framework of the nonlinear relativistic mean-field (RMF) theory using force parameters NL-SH. Calculations show that the RMF theory can describe experimental data of binding energies and radii for these nuclei. The RMF theory can also reproduce the level inversion of N=9 isotones well if the ρ tensor coupling is included. One-neutron halos in ¹⁵C and ¹⁴B are predicted.     

Description of the evolution of mixed-symmetry states in the N=78 isotonic chain with IBM2

The characteristics of the lowest mixed-symmetry states 2_ms⁺ and 1_ms⁺ for ¹³²Xe, ¹³⁴Ba and ¹³⁶Ce in the even-even N=78 isotones are investigated within the framework of the IBM2 model. The lowest mixed-symmetry state 2_ms⁺ levels for both a single isolated state in ¹³²Xe and ¹³⁶Ce and a fragmented state in ¹³⁴Ba are reproduced by the predictions. The agreement between the IBM2 calculation and the experimental values is good for the B(E2) and B(M1) transition probabilities both quantitatively and qualitatively. The predicted summed B(M1) strength follows the experimental data, remaining nearly constant as a function of proton number along the chain of the N=78 isotones.     

Microscopic origin of collective exponentially small resistance states

The formation of ‘zero’ (exponentially small) resistance states (ESRS) in high mobility two-dimensional electron systems (2DES) in a static magnetic field B and subjected to strong microwave (MW) radiation has attracted great theoretical interest. These states appear to be associated with a new kind of energy gap Δ. Here I show that the energy gap Δ is explained by a microscopic quantum model that involves the Prime Number Theorem, hitherto reserved for only mathematical contexts. The model also contains the zeroes of the zeta function, and explains the physical origin of the Riemann hypothesis.     

First identification of excited states in the N = Z nucleus 70Br

Excited states in the T_z = 0 nucleus ⁷⁰Br have been investigated using the reaction ⁵⁸Ni(¹⁶O,1p3n). % rays were detected with one EUROBALL CLUSTER detector and three single HPGe detectors. Charged particles and neutrons were registered with the Rossendorf silicon ball and six modules of the EUROBALL neutron wall, respectively. The identification of % transitions in ⁷⁰Br is based on the analysis of %%-proton-neutron coincidences. A level scheme of ⁷⁰Br has been established for the first time. It shows a multiplet-like structure of probably isospin T = 0 while T = 1 isobaric analogue states are not observed.     

Inhibited transitions and isomeric states in the N = 50 isotones

Measured E2 transition rates in the N = 50 isotones (⁹⁰Zr–⁹⁴Ru) are satisfactorily reproduced by a shell model 0699 0 with proton configurations (p_1/2g_9/2)ⁿ. The inhibited 8⁺→6⁺ E2 transition in ⁹⁴Ru and its connection with seniority mixing is discussed. Isomeric states are predicted in ⁹¹Nb and ⁹³Tc. 0699     

Restoration of pseudo-spin symmetry in N = 32 and N = 34 isotones described by relativistic Hartree-Fock theory

The restoration of pseudo-spin symmetry(PSS) along the N = 32 and N = 34 isotonic chains and the physics behind are studied by applying the relativistic Hartree-Fock theory with the effective Lagrangian PKA1. Taking the proton pseudo-spin partners(π2s_(1/2), π1d_(3/2)) as candidates, the systematic restoration of PSS along both isotonic chains is found from sulphur(S) to nickel(Ni), while an obvious PSS violation from silicon(Si) to sulphur is discovered near the drip lines. The effects of the tensor force components are investigated, introduced naturally by the Fock terms, which can only partially interpret the systematics from calcium to nickel, whereas they fail for the overall trends. Further analysis following the Schr?dinger-like equation of the lower component of Dirac spinor shows that contributions from the Hartree terms dominate the overall systematics of the PSS restoration. Such effects can be self-consistently interpreted by the evolution of the proton central density profiles along both isotonic chains. In particular, the PSS violation is found to tightly relate to the dramatic changes from the bubble-like density profiles in silicon to the central-bumped ones in sulphur.     

Microscopic description of mixed-symmetry states in nearly spherical nuclei

We adopt the quasiparticle-phonon model to investigate the phonon content and the proton-neutron symmetry of low-lying states recently discovered in nuclei around shell closure. The results are in overall agreement with experiments and consistent with the interacting boson model.     

Microscopic description and excitation of unitary alalog states

A microscopic investigation in a self-consistent particle-hole model reveals approximate unitary analog states in spite of large symmetry breaking. The K-nucleus elastic scattering and (K^?, π^?) excitation of these states are studied, showing strong surface effects.