摘要:

We show that, starting from density‐dependent nucleon‐nucleon interactions (extended Skyrme forces), one is able to construct an interaction that leads to correct saturation properties in the nucleus and also behaves as a good effective interaction in describing low‐lying excitations. This is illustrated in various mass regions. In those regions where many protons and neutrons determine the nuclear structure, one has to resort on collective model descriptions. We shortly point out the importance of symmetry considerations (the Interacting‐Boson model). More in particular, we concentrate on those modes of motion where the interplay of protons and neutrons is dominant: the M1 scissor mode, intruder 0+excitations and shape coexistence. Results for the Cd region, the Pb region and the N=20 nuclei are presented.

ISSN:0094-243X    

DOI:10.1063/1.41292

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The specific properties of the quasiparticle‐phonon nuclear model with a phonon operator consisting of the electric and magnetic parts are discussed. It is asserted that magnetic states in deformed nuclei cannot be consistently treated without interactions of the electric type. The structure of nonrotational states of doubly even deformed nuclei is discussed. Distribution of E2 and E3 strength among low‐lying states is exemplified by238U.

ISSN:0094-243X    

DOI:10.1063/1.41170

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Consequences of the validity of the pseudo‐spin concept, which follows from the fact that the strength of the spin‐orbit interaction in the single‐particle shell‐model hamiltonian is approximately four times the strength of the orbit‐orbit term, are reviewed. In particular, it follows that the pseudo‐LS‐coupled scheme is the natural choice for a many‐particle shell‐model theory of heavy nuclei. Going beyond the pseudo‐LS scheme to situations where deformation inducing terms dominate the residual two‐body interaction, as is the case for deformed nuclei of the rare earth and actinide regions, the pseudo‐SU(3) scheme and its multi‐ℏ&ohgr; extension, the pseudo‐symplectic model, are good many‐particle shell‐model theories. Some preliminary results for238U are presented. The contribution of intruder states to enhanced quadrupole collectivity in deformed nuclei is also considered.

ISSN:0094-243X    

DOI:10.1063/1.41280

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Use of the pseudo‐spin transformation in the shell model scheme leads to the approximate validity of the pseudo‐L quantum number in odd‐A nuclei. The empirical signatures of this symmetry are discussed and it is shown that the transformation gives rise to a new set of intensity relationships for E2 transitions in strongly deformed systems.

ISSN:0094-243X    

DOI:10.1063/1.41257

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.41221

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The essential role of the valence, residual p‐n interaction in the development of collectivity, though long known in general terms, has recently become increasingly apparent. A brief review of the p‐n interaction is given, including some very basic nuclear data that illustrate its effects and the phenomenological NpNnscheme and the P‐factor. This is followed by a discussion of recent experimental extractions of p‐n matrix elements throughout the periodic table and theoretical efforts to understand them, in terms of both Shell and Nilsson models.

ISSN:0094-243X    

DOI:10.1063/1.41241

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The purity of intrinsic states of nuclei with respect to a proton‐neutron boson symmetry (F‐spin) is shown to be largely determined by the difference between proton and neutron deformations and not by whether the Hamiltonian is an F‐spin scalar. Upper and lower bounds on F‐spin mixing in the ground state band of165Ho are estimated using recent pion single‐charge‐exchange data.

ISSN:0094-243X    

DOI:10.1063/1.41205

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The role of octupole and dipole degrees of freedom in the description of the large B(E1) rates measured in theA∼100 and 150 regions is reviewed. We find that algebraic methods offer a simple picture and a good description of most observed phenomena.

ISSN:0094-243X    

DOI:10.1063/1.41176

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Fragmentation of the low energy octupole state and its implications for studies of the systematic behavior of 31−states are discussed. The use of octupole centroids for study of the systematic behavior of octupole states is introduced and applied to studies of the A=150 and 190 regions. In addition, a survey of the dependence of octupole fragmentation on quadrupole deformation is presented. This survey demonstrates that 31−state behavior is generally not strongly affected by fragmentation when &bgr;2<0.3; however, fragmentation effects in the Pt isotopes seem to strongly violate this general rule.

ISSN:0094-243X    

DOI:10.1063/1.41187

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The M1 strength distribution is studied in rare‐earth nuclei, starting from the Nilsson model and using the Quasi‐Particle Random Phase Approximation (QRPA), including monopole as well as quadrupole pairing, Coriolis mixing and residual quadrupole and spin‐isospin interactions. For the nucleus164Dy the importance and effect of the different terms in the Hamiltonian are studied. Results are compared with experimental observations. Special attention is given to the higher‐lying spin strength in view of a recent (p,p’) experiment performed at TRIUMF on154Sm.

ISSN:0094-243X    

DOI:10.1063/1.41158

出版商:AIP    

年代:1991

数据来源: AIP