A nucleon-pair and boson coexistent description of nuclei

We study a mixture of s-bosons and like-nucleon pairs with the standard pairing interaction outside an inert core. Competition between the nucleon-pairs and s-bosons is investigated in this scenario. The robustness of the BCS-BEC coexistence and crossover phenomena are examined through an analysis of pf-shell nuclei with realistic single-particle energies, in which two configurations with Pauli blocking of nucleon-pair orbits due to the formation of the s-bosons is taken into account. When the nucleon-pair orbits are considered to be independent of the s-bosons, the BCS-BEC crossover becomes smooth, with the number of the s-bosons noticeably more than that of the nucleon-pairs near the half-shell point, a feature that is demonstrated in the pf-shell for several values of the standard pairing interaction strength. As a further test of the robustness of the BCS-BEC coexistence and crossover phenomena in nuclei, results are given for B(E2; 0_1~+→2_1~+) values of even-even~(102-130) Sn with~(100)Sn taken as a core and valence neutron pairs confined within the 1d_(5/2), 0g_(7/2), 1d_(3/2), 2s_(1/2), 1h_(11/2)orbits in the nucleon-pair orbit and the s-boson independent approximation. The results indicate that the B(E2) values are reproduced well.     

Some Electromagnetic Transition Properties of Odd-A Europium Isotopes

In this work, we analyze the positive parity of states of odd-A Eu isotopes within the framework of interacting boson fermion model （IBFM-1）. The result of an IBFM-1 multilevel calculation with the 3s1/2, 2d3/2, 2d5/2, and 1g7/2 single panicle orbits is reported for the positive parity states of the odd-A Eu isotopes. A/so, an IBM-1 calculation is presented for the low-lying states in the even-even 152-154Sm core nucleus. The energy levels and B（E2） transition probabilities are calculated and compared with the experimental data. It is found that the calculated positive parity low spin state energy spectra of the odd-A Eu isotopes agree quite well with the experimental data.     

Description of the Structure of 88-96Sr in the IBM

The neutron-rich even-even Sr isotopes are studied in the interacting boson model. The semi-closed nucleus ⁸⁸Sr is studied in the framework of the IBMI, and ^90-96Sr are studied in the neutron-proton interacting boson model. The spectrum and E2, M1 transition properties are calculated and compared with experiment.     

Symmetries of the interacting boson model

This contribution reviews the symmetry properties of the interacting boson model of Arima and Iachello. While the concept of a dynamical symmetry is by now a familiar one, this is not necessarily so for the extended notions of partial dynamical symmetry and quasi dynamical symmetry, which can be beautifully illustrated in the context of the interacting boson model. The main conclusion of the analysis is that dynamical symmetries are scarce while their partial and quasi extensions are ubiquitous.     

Generalized interacting boson model and the collective behaviour in nuclei

The effect of including the high spin bosons on the manifestation of collective behaviour in nuclei is examined by plotting theB(E2; 2⁺→0⁺) rates as a function of neutron number for various values ofη, whereη is the highest angular momentum of the bosons included in the calculation.B(E2; 2⁺→0⁺) values of a large number of nuclei in various regions of the nuclear periodic table are calculated with a single value for the effective charge in the generalized scheme. Irreducible representations of SU(3) contained in the symmetric partition [N] of U(15) are worked out for integersN uptoN=15, to enable the explicit inclusion of theg boson into calculations. The experimentally observed odd-K bands in²³⁴U and¹⁸⁴W are described as a direct consequence of theg boson.     

三玻色子核的核谱研究

在相互作用玻色子模型的基础上,用玻色子表面δ力作为玻色子之间的有效相互作用,计算了一些三玻色子核的核谱,同时也计算了E2约化跃迁几率,结果令人满意.表明这种模型是成功的.     

原子核的形状相变

简要回顾原子核形状相变研究的现状，并将相干态理论与角动量投影方法相结合，在不区分质子玻色子和中子玻色子的相互作用玻色子模型（IBM-1）框架下，对角动量驱动的轴对称情况下的具有U（5）、SU（3）对称性以及两种对称性之间过渡区的原子核的形状相变进行了具体研究。We review the status of the research of nuclear shape phase transitions in this paper. Meanwhile, by taking the coherent state theory and angular momentum projection method, we study the shape phase transitions of axially symmetric even-even nuclei with U（5） symmetry, SU（3） symmetry and those in the transitional region of the two symmetries in the framework of Interacting Boson Model-1 （IBM-1）, which does not distinguish the proton bosons from neutron bosons.     

<Emphasis Type="Italic">SU</Emphasis>(5) symmetry of<Emphasis Type="Italic">spdfg</Emphasis> interacting boson model

The extended interacting boson model withs-, p-, d-, f- andg-bosons included (spdfg IBM) is investigated. The algebraic structure including the generators, the Casimir operators of the groups at theSU(5) dynamical symmetry and the branching rules of the irreducible representation reductions along the group chain are obtained. The typical energy spectrum of the symmetry is given.     

Nuclear deformations from inelastic α-scattering on rare earth nuclei at energies near the Coulomb barrier

Alpha particles in the energy range of 10–20 MeV and scattered at various angles were used to excite the 0⁺, 2⁺, 4⁺ members in the ground state bands of ¹⁵²Sm, ¹⁵⁴Sm and ¹⁸⁶W. The measured excitation probabilities for bombarding energies below the Coulomb barrier were analyzed in the framework of Coulomb excitation theory. The resulting matrix elements of the E2 and E4 multipole operators were interpreted in terms of charge deformation parameters β^cλ = 2, 4. The cross sections for higher energies were analyzed in terms of the deformed optical potential and resulted in potential deformation parameters β^pλ = 2, 4. The two sets of deformation parameters show the same general trend of variation with target mass number. Still, significant differences are observed in some particular cases.     

Nuclear structure at the proton drip line: Advances with nuclear decay studies

The study of nuclear decay modes reveals a large panel of nuclear structure phenomena and allows us to investigate the behaviour of the atomic nucleus with an extreme imbalance of the number of neutrons and protons with respect to stable nuclei. In the present paper, we review certain aspects of β-delayed decay modes, of one- and two-proton radioactivity, and of the experimental techniques which allowed us to get deep insights into the organisation of the atomic nucleus. In most cases, the study of these decay modes is the only means to obtain the information searched for. The investigation of nuclear decay modes is shown to be a powerful tool to study the most proton-rich nuclei and their nuclear structure.     

1/N展开技术的一些应用

引入高阶修正项的1/N展开技术所推导出的sdIBMl的能谱和E2跃迁概率的理论公式,应用于铀区的一些核,与实验符合令人满意.结果表明,高阶修正项对于重现E2跃迁十分重要.     

The Structure of the Neutron-Rich Nd Isotopes in the IBM

The spectra and E2 transition properties of ^146-156Nd isotopes are studied in the interacting boson model in the light of new experimental data. It is found that ^146-150Nd are in the transition from the vibrational limit to the rotational limit. From ¹⁵²Nd onward, the isotopes are nearly perfect rotors. Possible deformation saturation is discussed in the interacting boson model.     

Elastic and inelastic scattering of polarized protons from even n=82 nuclei near isobaric analog resonances

Excitation curves for the elastic and the inelastic scattering of polarized protons on the target nuclei ¹³⁸Ba, ¹⁴⁰Ce, ¹⁴²Nd and ¹⁴⁴Sm have been measured in the energy region of prominent isobaric analog resonances. A detailed analysis of the data is presented. Definite J^π assignments are given for a number of parent analog states. Spectroscopic factors and amplitudes for configurations with the core in the ground state or in the 2₁⁺ excited state are derived from the elastic and inelastic proton decay amplitudes. They show consistency with sum rules including orthogonality conditions. Different methods for the-calculation of single particle decay widths have been applied. The qualitative agreement with present unified model calculations is remarkable; an overestimattion of the weak coupling structure, however, becomes apparent.     

Nuclear structure of neutron-rich nuclei near closed shells from excited-state g-factor measurements

New techniques to measure the g factors of picosecond-lived excited states of neutron-rich nuclei produced as radioactive beams are discussed along with their applications to study nuclear structure near ¹³² ₅₀Sn₈₂ and in the region between N=20 and N=28.     

Nuclear Structure and Electromagnetic Transitions Investigation in Er Isotopes within Framework of Interacting Boson Model

Interacting Boson Model-2(IBM-2)is used to determine the Hamiltonian for Er nuclei.Fit values of parameters are used to construct the Hamiltonian,energy levels and electromagnetic transitions(B(E2),B(M1))multipole mixing ratios(δ(E2/M1))for some even-even Er nuclei and monopole transition probability are estimated.New ideas are used for counting bosons number at N=64 and results are compared with previous works.     

Nuclear structure around 80Zr

Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons （N = Z）. Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model（PSM）together with a relativistic Hartree-Bogoliubov （RHB） theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces and ground state bands are calculated. It is shown that shape coexistence occurs in all of these nuclei. Moreover, we find that the residual neutron-proton interaction strongly affects the ground state band of 80Zr; however, it slightly modifies those of 82Zr and 84Zr.     

Nuclear structure effects in the feeding of yrast states of Gd,Dy and Er nuclei

The population of the yrast and near-yrast levels in Gd, Dy and Er nuclei has been investigated experimentally in (heavy ion, xn) reactions through high-resolution γ-ray intensity measurements. A clear difference between non-rotor (N ? 86) and rotor nuclei (N > 86) is evident from the data. For the non-rotor nuclei we define the spin value I_sat below which the yrast population saturates. One finds that I_sat is independent of the bombarding energy when the latter becomes sufficiently high. We discuss the feeding pattern in relation to the single-particle structure of the yrast and near-yrast levels and in relation to the effect of shape changes, including the possibility of superdeformed shapes at high spin.     

In-beam study and structure of the N = 82 nucleus 141Pr

High-spin states in ¹⁴¹Pr have been studied in the reactions ¹³⁹La(α, 2n)¹⁴¹Pr and ¹⁴⁰Ce(d, n)¹⁴¹Pr. Using in-beam spectroscopic methods energies, intensities, excitation functions, γγ coincidences, time and angular distributions and the linear polarization of γ-rays as well as conversion electron spectra were measured. Positive- and negative-parity states of ¹⁴¹Pr have been established for spin values up to $\text{J =}\text{27}\text{2}$ and E_x < 4750 keV including 19 news lvels. For three levels ns-lifetimes were determined. The experimental data on positive-parity states are in remarkable agreement with shell-model predictions. In the case of positive-parity states no evidence for particle-core coupling is found. The shell-model investigation suggests, however, that the negative-parity states in ¹⁴¹Pr as well as in ¹⁴³Pm can be explained by particle-core coupling.