Level density for doubly odd deformed nuclei

The level density for doubly odd deformed nuclei near B_n is calculated within the framework of the semi-microscopic approach. The calculated values are found to be in good agreement with the experimental ones. It is shown that for the I ? 1 states it is important to take into account rotational motion.     

Semiclassical limit for a truncated Hamiltonian

In the numerical calculation of the eigenenergies of a polynomial Hamiltonian, the majority of the levels depend on the cutoff of the basis used. By analyzing the finite Hamiltonian matrix as corresponding to a classical "Action Billiard" we are able to explain several features of the full spectrum using semiclassical periodic orbit theory. There are a large number of low-period orbits which interfere at the higher energies contained in the billiard. In this range the billiard becomes more regular than the untruncated Hamiltonian, as reflected by the Berry-Robnik level spacing distribution. (c) 1996 American Institute of Physics.     

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.     

Particle-rotor model for doubly odd transitional nuclei of the Tl-region

A model has been investigated describing a situation in which two noninteracting high-j Nilsson-BCS quasiparticles move in the deformed field of an axially and reflection symmetric rotor. According to the positions of thej-shells with respect to the proton and neutron Fermi surfaces structures of different character emerge referred to as semi- and doubly-decoupled. In particular, strongly Coriolis-distorted bands recently reported in doubly odd Tl nuclei are discussed. Also \(\tilde \pi h_{9/2} \) bands in neighbouring odd mass Tl isotopes are analysed on the same footing. It is shown that the pronounced odd even staggering of the transition energies can be understood as a specific quantal feature associated with the Coriolis interaction.     

A simple model for doublet bands in doubly odd nuclei

Nuclear structure of doublet bands in doubly odd nuclei with mass A ∼ 130 is investigated within the framework of a simple model where the even-even core couples with a neutron and a proton in intruder orbitals through a quadrupole-quadrupole interaction. The model reproduces quite well the energy levels of doublet bands and electromagnetic transitions. The staggering of the ratios B(M1;I → I - 1)/B(E2;I → I - 2) of the yrast bands turns out to be described by the chopsticks-like motion of two angular momenta of the unpaired neutron and the unpaired proton when they are weakly coupled with the core.-1 An erratum to this article is available at .     

SU(3) coupling schemes for odd-odd nuclei in the interacting boson – fermion – fermion model with both odd proton and odd neutron in natural parity orbits

The SU^BFF(3) dynamical symmetry limits of interacting boson – fermion – fermion model are identified and they are appropriate for heavy deformed odd – odd nuclei for configurations with both the odd proton and odd neutron occupying all the natural parity orbits in the corresponding valence shells. There are three symmetry limits and their correspondence with two quasi-particle (proton-neutron) Nilsson configurations is established; one of the limits mixes both Nilsson n_z's and Λ's and other two limits mix only Nilsson Λ's. The ¹⁹¹Ir (d,t) ¹⁹⁰Ir single nucleon transfer spectroscopic strengths are well described by one of the symmetry limits that mixes only Nilsson Λ's. Received: 22 June 1998     

Ground state correlations and structure of odd spherical nuclei

It is well known that the Pauli principle plays a substantial role at low energies because the phonon operators are not ideal boson operators. Calculating the exact commutators between the quasiparticle and phonon operators, one can take into account the Pauli principle corrections. Besides, the ground state correlations due to the quasiparticle interaction in the ground state influence the single-particle fragmentation as well. In this paper, we generalize the basic equations of the quasiparticle-phonon nuclear model to account for both effects mentioned. As an illustration of our approach, calculations on the structure of the low-lying states in ¹³³Ba have been performed. The text was submitted by the authors in English.     

Multi-band spectra of odd and even nuclei of the s-d shell

The energy levels of^{21, 23}Na,^{22, 23}Ne,^{24, 28}Mg and^{25, 29}Al are obtained by mixing various bands using the projected deformed Hartree-Fock (DHF) method. Solutions having minimum energies are found to be prolate for all the nuclei considered here. Higher bands are obtained either by considering particle-hole excitations or oblate solutions. These various bands are mixed using the projection method and care has been taken to orthogonalize the bands. The interactions used in this study are those given by Kuo, Preedom-Wildenthal (PW) and WHMK interactions. The last one seems to give good results for most of the nuclei considered here. Not only are the lowest bands well-reproduced but the second lowest bands agree reasonably well in most nuclei. The third lowest ones obtained in some nuclei are not yet observed as complete bands. However, K obtained for the third band seems to be correct. A comparison with shell model calculations—which are numerically exhausting—shows similar results for the lowest band. However, the agreement of the second band varies from nucleus to nucleus. A comparison between matrix elements of the interactions is made to analyze the results.     

Mean-field mass parameters for odd nuclei within the GOA+GCM approach

The GCM mass parameters for the heavy odd-nuclei region within the mean-field hamiltonian approximation have been calculated. The influence of the energy window size, the level crossing and the projection onto good particle number effects have been analyzed.     

Description of odd transitional nuclei in terms of core-quasiparticle models

A general core-quasiparticle coupling (CQPC) formalism is presented that properly accounts for the particle-hole structure in odd-A transitional nuclei. The method is a consequent generalization of the Coriolis-coupling approach. The formalism is applied to the coupling of a quasiparticle to the γ = 30° triaxial rotor and to a γ-unstable core. A comparison with the experimental ¹⁹¹Pt spectrum shows that the odd particle is not a sufficiently sensitive probe to distinguish between the two core models.     

Magnetic moments of low-lying states in medium weight odd nuclei

The magnetic moments of several short-lived states in¹⁰³Rh,^1111113Cd and^1231125Te isotopes have been measured by the transient field technique. The results, together with those obtained earlier in the^1071109Ag isotopes, have been compared to predictions of various models and calculations. In the Z=45, 47 isotopes, the odd proton seems to deform the vibrational core. The data are best explained within the framework of a triaxially deformed nucleus. In the odd neutron isotopes with 50<N<82, and Z=48, 52, weak coupling states coexist with single particle states in a mix of configurations.     

Band coupling and crossing in nuclei

A model of coupled rotational bands, including three types of phonons, β, γ and S(K^π = 1⁺ or 0⁺), is proposed and applied to a number of even-even rare earth back-bending nuclei. It reproduces the most complicated experimentally known multiple-band crossings in ¹⁵⁴Gd, ¹⁵⁶Dy, ¹⁶⁴Er and the clockwise circling of the yrast B(E2) values (versus ω²) in back-bending nuclei. The direct coupling strengths, derived from a fit to experimental data, are discussed in detail.     

Extension of the multiphonon method to odd mass deformed nuclei

The multiphonon method based on one type of phonon is extended to odd mass nuclei. The formulas for the matrix elements of one and two body operators are given.     

Inequalities for light nuclei in the Wigner symmetry limit

Using effective field theory we derive inequalities for light nuclei in the Wigner symmetry limit. This is the limit where isospin and spin degrees of freedom can be interchanged. We prove that the energy of any three-nucleon state is bounded below by the average energy of the lowest two-nucleon and four-nucleon states. We show how this is modified by lowest-order terms breaking Wigner symmetry and prove general energy convexity results for SU(N). We also discuss the inclusion of Wigner-symmetric three- and four-nucleon force terms.     

On the interpretation of rotational bands in odd actinide nuclei

While the cranked quasiparticle model gives too large alignment of angular momentum for the ground state bands of ²³⁵U and ²³⁷Np, the empirical alignments are well reproduced in a quasiparticle plus rotor model with a rotation dependent interaction between core and quasiparticle. This model also gives better agreement with the data than a cranked quasiparticle model with Coriolis attenuation.     

Generalized hybrid derivative coupling model for finite nuclei

The generalized hybrid derivative coupling model has been applied to explore various ground state properties of different nuclei. In this work we have confined our calculation only to the model characterized by the hybridization parameter α = 1/4 which gives better results than the other models of the same class, as we have seen earlier, for nuclear matter calculations. The binding energy, single-particle energy spectra, density and charge radii of different doubly closed nuclei like ¹⁶O, ⁴⁰Ca, ⁴⁸Ca, ⁹⁰Zr, ¹³²Sn, ²⁰⁸Pb have been studied. The success of this model, in describing the doubly closed nuclei, motivates us to extend this calculation further in the case of open shell nuclei after incorporating the pairing interaction and using a BCS transformation. We have calculated the binding energy for such nuclei. We have also studied the isotopic shift for different Pb isotopes with respect to ²⁰⁸Pb. We have compared our results with the other standard theoretical results as well as with the experimental values. Received: 18 August 2000 / Accepted: 13 April 2001     

Particle-vibration coupling and many-particle correlation in nuclei

The formation of many-particle clusters within atomic nuclei as a result of the coupling between particle and vibrational modes has been investigated. Expressions for the formation probabilities have been obtained for different excitation energies of the nuclei, characterized by the nuclear temperature. The methods used in the analysis are those of the double-time temperature Green function and the Fredholm method of solving integral equations.