Rare-earth nuclei and the pseudo-SU(3) model

An extended version of the pseudo-SU(3) model is used to describe low-energy positive-parity states of three rare-earth nuclei in a full proton-neutron formalism. Along with other residual interactions, the Hamiltonian includes the pairing which induces mixing between different representations of SU(3). Excitation energies, B(E2) values, B(M1) values, quadrupole moments, andg _R factors of¹³⁶Xe,¹³⁸Ba, and²⁰⁴Hg are calculated in a truncation free environment and the results are compared with the experimental data and other theories.     

Excited states of deformable nonaxial odd nuclei

Rotationally single-particle and vibrational excitations of deformable nonaxial odd nuclei are investigated with allowance for the interaction of collective and single-particle states. The ratios of excitation energies, of reduced probabilities of E2 transitions, and of quadrupole moments for deformed nonaxial odd nuclei are calculated up to high-spin states.     

The structure of ground states of odd-odd nuclei160Tb,182Ta,182Re and of isomer182mRe

The ground states of odd-odd nuclei¹⁶⁰Tb,¹⁸²Ta and¹⁸²Re and the isomeric state^182mRe are interpreted in terms of the Nilsson nuclear model. The conclusions about the structure of these states were drawn from the experimental results obtained in the study of their decay to the neighbouring even-even nuclei as well from the systematics of single-particle proton and neutron states in neighbouring odd-mass nuclei. The agreement between experimental and calculated values of the moments of inertia of these states is demonstrated.Dúbravská cesta, Bratislava, Czechoslovakia.     

Properties of single-particle states in the 208Pb region

The properties of single-particle states in the ²⁰⁸Pb region are obtained by subtracting from the empirical values the dressing effects of the multipole particle-hole and pairing phonons. Use is made of the particle-vibration formalism. Single-particle energies, one-body transfer spectroscopic factors and effective quadrupole charges are examined within this framework.     

奇质量核的超越平均场玻色子费米子模型描述(英文)

对近年发展起来的一个基于核密度泛函理论和粒子核心耦合方案来计算中重质量奇A核谱性质的理论方法进行了评述。该方法首先在平均场层面通过选择合适的能量密度泛函和对力结构来自洽求解偶偶核心的势能曲面、球单粒子能级和奇粒子占有率,进一步将得到的结果作为微观输入来建立相互作用玻色子费米子模型哈密顿量,其中三个与粒子核心耦合强度相关的参数需要通过拟合一些特定奇质量核低激发谱数据来最终确定。通过对轴形变奇质量Eu同位素的低激发能谱和电磁跃迁几率的系统研究来说明该模型方法的有效性。另外,还讨论了该方法在描述轴形变奇质量核形状相变以及描述丰中子奇质量Ba同位素中八极关联方面的应用。A recently developed method for calculating spectroscopic properties of medium-mass and heavy atomic nuclei with an odd number of nucleons is reviewed, that is based on the framework of nuclear energy density functional theory and the particle-core coupling scheme. The deformation energy surface of the eveneven core, as well as the spherical single-particle energies and occupation probabilities of the odd particle(s), are obtained by a self-consistent mean-field calculation with the choice of the energy density functional and pairing properties. These quantities are then used as a microscopic input to build the interacting bosonfermion Hamiltonian. Only three strength parameters for the particle-core coupling are specifically adjusted to selected data for the low-lying states of a particular odd-mass nucleus. The method is illustrated in a systematic study of low-energy excitation spectra and electromagnetic transition rates of axially-deformed odd-mass Eu isotopes. Recent applications of the method, to the calculations of the signatures of shapes phase transitions in axially-deformed odd-mass nuclei, octupole correlations in neutron-rich odd-mass Ba isotopes, are discussed.     

Oblique-basis shell-model calculations

A one-dimensional harmonic oscillator in a box is used to introduce the oblique-basis concept. The method is extended to the nuclear shell model by combining traditional spherical shell model states, which yield a diagonal representation of the usual single-particle interaction, with SU(3) shell model collective configurations that track deformation. An application to ²⁴Mg, using the realistic two-body interaction of Wildenthal, is used to explore the validity of this mixed-mode shell-model scheme. The theory is also applied to lower pf-shell nuclei, ^44–48Ti and ⁴⁸Cr, using the Kuo-Brown-3 interaction. These nuclei show strong SU(3) symmetry breaking due mainly to the single-particle spin-orbit splitting. Nevertheless, the results also show that yrast band B(E2) values are insensitive to fragmentation of SU(3) symmetry. Specifically, the quadrupole collectivity as measured by B(E2) strengths remains high even though the SU(3) symmetry is rather badly broken. The results suggest that an oblique-basis mixed-mode shell-model theory may be useful in situations where competing degrees of freedom dominate the dynamics.     

Parameters of the proton shell structure of the <Superscript>40,42,44,46,48</Superscript>Ca nuclei and their analysis within the dispersive optical model

By matching data on proton-stripping and proton-pickup reactions occurring on the same nuclear species, new experimental results for single-particle energies, occupation numbers, and fragmentation widths of proton states in the vicinity of the Fermi energy are obtained for the even-even isotopes ^{40,42,44,46,48}Ca These results, along with the experimental values determined in the relevant (p, 2p) reaction for the single-particle energies of deep hole states in ⁴⁰Ca, are analyzed on the basis of the dispersive-optical-model version proposed in the present study. The results of this analysis are compared with the predictions of various nuclear models, including the relativistic mean-field model.     

α-clustering in Be isotopes

The Be chain of isotopes is investigated within the Sernimicroscopic Algebraic Cluster Model (SACM). For that the SACM is extended to odd-mass p-shell nuclei. We show that the main features of the Be isotopes can be well explained. Though for the neutron halo nucleus ¹¹Be some problems remain, the shell model still can describe the rough structures of these nuclei. In ¹¹Be a shell inversion takesplace reflecting the high deformation of the system. The quadrupole—quadrupole interaction plays a dominant role in p-shell nuclei.     

Investigation of the neutron shell structure of the even-even isotopes <Superscript>40–56</Superscript>Ca within the dispersive optical model

Within the method of matching experimental data obtained in the neutron-stripping and neutron-pickup reactions on ^{40,42,44,46,48}Ca isotopes, the single-particle energies and probabilities that neutron states are filled are obtained for the even-even calcium isotopes. These data are analyzed within the dispersive optical model, and good agreement between the calculated and experimental values of the energies of states is obtained. The dispersive optical potential is extrapolated to the region of the unstable ^50,52,54,56Ca nuclei. The calculated single-particle energies of bound states in these isotopes are compared with the results of the calculations within the multiparticle shell model, the latter predicting a new magic number N = 34 for Z = 20 nuclei.     

Effect of high-lying configurations on the odd-parity spectrum of 16O

The effect on the 1?ω odd-parity spectrum of ¹⁶O of high-lying configurations is studied by including all states at 3?ω, and all states at 3?ω and 5?ω, in second-order perturbation theory. It is found that inclusion of the 3?ω states results in a lowering of the spectrum by about 2–3 MeV when the single-particle and single-hole energies are also calculated. By contrast the 5?ω states further affect the energy levels by $\text{1}\text{2}$ MeV or less. When the above calculations are repeated with experimental single-particle and single-hole energies no overall improvement in the spectrum is obtained. Adding a hard-core potential (whose inclusion does not alter the two-body phase shifts) to the Sussex interaction lowers the 1?ω spectrum by about 1 MeV, without including higher configurations.     

The promethium isotopes in the interacting boson-fermion model

We present a calculation of excitation energies, electromagnetic moments and transition rates and single-particle transfer amplitudes for the odd-mass promethium isotopes in terms of the interacting boson-fermion model. Model parameters are compared with those obtained for the neighbouring europium isotopes.     

An investigation of the properties of single-particle states in the second minimum of 237Pu

In connection with the recent measurement of the magnetic moments of the fission isomeric states in ²³⁷Pu, we investigate the following subjects: (i) The spin alignment of the lowest-lying states in a potential minimum which are populated by (α, 2nγ) reactions, and the fragment angular distributions in fission from isomeric states. (ii) The single-particle level scheme in a very deformed Woods-Saxon potential. (iii) The spin polarizability as a function of the quadrupole deformation.     

Investigation of special features of the neutron and proton shell structure of the isotopes 90,92,94,96Zr

The neutron and proton single-particle energies and the occupation probabilities for the valence states of the even-even isotopes ^90,92,94,96Zr are determined by matching data on nucleon-stripping and nucleon-pickup reactions on the same nucleus. The data obtained in this way suggest the magicity of the number N = 56 for Z = 40. The single-particle energies of all bound neutron and proton states in the ^90,92,94,96Zr nuclei are described within the experimental errors on the basis of the dispersive optical model.     

Shell model calculations of two to four identical-“particle” systems near 208Pb

The structure of the nuclei ^204–206Pb, ^210–212Pb, ²¹⁰Po, ²¹¹At, and ²¹²Rn is studied in terms of conventional nuclear shell models. An inert ²⁰⁸Pb core is assumed, and active particles (holes) are distuibuted in the low-lying single-particle (hole) orbits. Experimental single-particle energies are used for the one-body part of the effective residual interaction. Realistic interaction matrix elements developed for this mass region by Kuo and Herling are used for the matrix elements of the two-body part of the residual interactions. As much as possible, other effective one-body operators for electromagnetic observables are derived from experimental data on the single-particle (hole) nuclei ²⁰⁷Pb, ²⁰⁹Pb, and ²⁰⁹Bi. Observables treated are ground state binding energies, excitation energies, strengths for one- and two-particle transfers, and E2 and M1 observables. Generally, excellent agreement is found. The configuration mixing calculations do not remove anomalies in the magnetic moments of excited states in ²⁰⁶Pb and ²¹²Rn. Many states in these nuclei are predicted by the models which have not been observed as yet. It is found that a truncation scheme for doubly even nuclei treated here in which only seniority-0 and seniority-2 states are allowed is potentially very useful.     

Two- and three-quasiparticle states in the interacting boson model and a unified description of even- and odd- mass Hg isotopes

The formalism of the interacting boson-fermion approximation is extended to include two- and three-quasiparticle states. This model is used in a systematic study of the high-spin states in even- and odd-mass ^189–198Hg isotopes. The positive-parity states in these nuclei are described by coupling $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron states to an O(6) core, which offers a simple and parameter-free test of the boson-fermion interaction. Good agreement is obtained between the recent experimental results and the calculated energies, transition rates and g-factors.     

Low-spin states of odd-mass xenon isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson-fermion model. The result of an IBFM-1 multilevel calculation with the 2d_5/2, 1g_7/2, 3s_1/2, 2d_3/2 and 1h_11/2, single particle orbits is reported for the positive parity states of the odd-mass nucleus ^125–129Xe. Also, an IBM-1 calculation is presented for the low-lying states in the even-even ^124–128Xe core nucleus. The energy levels and B(E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low-spin state energy spectra of the odd-mass ^125–129Xe isotopes agree quite well with the experimental data.      

Description of even-even triaxial nuclei within the coherent state and the triaxial rotation-vibration models

The coherent state model (CSM) and the triaxial rotation-vibration model (TRVM) are alternatively used to describe the ground, γ and β bands of ²²⁸Th. CSM is also applied to the nuclei ¹²⁶Xe and ¹³⁰Ba, which were recently considered in TRVM. The two models are compared with respect to both their underlying assumptions and to their predicted results for energy levels and E2 branching ratios. Both models describe energies and quadrupole transitions of ²²⁸Th equally well and in good agreement with experiment, if the 0₃⁺ level at 1120 keV is interpreted as the head of the β band. The other two 0⁺ levels at 832 and 939 keV are most likely not of a pure quadrupole vibration nature as has been already pointed out in the literature.     

An analysis of odd-mass rare-earth nuclei using angular momentum projection

A systematic analysis of positive-parity rotational states in odd-mass rare-earth nuclei is presented. The theory used is microscopic in the true sense and conserves both the angular momentum and the particle number as the projection technique is applied. The hamiltonian contains the quadrupole pairing interaction (in addition to the conventional (monopole) pairing and Q · Q forces) which plays an essential role in odd-mass as well as in doubly-even nuclei. Agreement between theory and experimental data is excellent.