摘要:

The role of dynamic symmetries in the structure of superdeformed nuclei is briefly discussed.

ISSN:0094-243X    

DOI:10.1063/1.42591

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The pseudo‐spin concept is reviewed: What it is and is not, what it does and does not do, and what it means and does not mean are the issues addressed. Specifically, it is a special basis for carrying out microscopic (fermion) shell‐model calculations in heavy nuclei which exploits the fact that for the single‐particle shell‐model hamiltonian the strength of the spin‐orbit interaction is about four times the strength of the orbit‐orbit term and therefore these two can be transformed into an equivalent pseudo hamiltonian form with a very small spin‐orbit interaction. As a consequence, the pseudo‐LS‐coupled (space‐spin) scheme emerges as the natural choice for a many‐particle shell‐model theory of heavy nuclei. Going beyond the pseudo‐LS coupling 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 shown to be good many‐particle shell‐model theories. A list of applications already completed and some currently underway is given along with results which show that the scheme can be used to reproduce the B(E2:2+ → 0+) strength in238U without the use of an effective charge but that this requires as much as ∼40% vertical (≥2ℏ&ohgr;) mixing.

ISSN:0094-243X    

DOI:10.1063/1.42577

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Spectroscopy of superdeformed nuclear states opens up an exciting possibility to probe new properties of the nuclear mean field. In particular, the unusually deformed atomic nucleus can serve as a microscopic laboratory of quantum‐mechanical symmetries of a three dimensional harmonic oscillator. The classifications and coupling schemes characteristic of weakly deformed systems are expected to be modified in the superdeformed world. The ‘‘superdeformed’’ symmetries lead to new quantum numbers and new effective interactions that can be employed in microscopic calculations. New classification schemes can be directly related to certain geometrical properties of the nuclear shape.

ISSN:0094-243X    

DOI:10.1063/1.42583

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Several new rotational bands with energy spacings typical for superdeformed shapes have been identified in Tl and Pb nuclei. Their &ggr;‐ray transition energies are often identical or closely related to those of192Hg or193Tl. The resulting dynamic moments of inertia are much more similar than experienced in any other case. Spins, although not directly measured in any superdeformed band, can be assigned with the help of a rigid‐rotor expansion of the &ggr;‐ray energies. The alignments obtained as spin differences with respect to the reference band are quantized for rotational frequencies above 0.2 MeV.

ISSN:0094-243X    

DOI:10.1063/1.42557

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A brief reminder is given of the evidence for the existence of octupole correlations in the superdeformed shape of193Hg. It is pointed out that comparison of the data on the superdeformed bands in19Hg with Cranked Shell Model calculations gives firm assignments to the signatures and parities of these bands. The spin assignments obtained are in agreement with the spin assignments given by projecting the SD bands back to zero rotational frequency and assuming the intrinsic alignment i0is zero. These spin asssignments leave ‘‘identical’’ bands in191Hg,193Hg and194Hg with a surplus 1ℏ of spin relative to the superdeformed core nucleus192Hg. This extra 1ℏ of alignment is not understood.

ISSN:0094-243X    

DOI:10.1063/1.42565

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.42568

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A completely microscopic approach of deformation and superdeformation in nuclei based on the constrained mean field theory is presented, together with applications to three Mercury isotopes. The Hartree‐Fock‐Bogolyubov theory of nuclear structure is employed with the D1S effective interaction in order to derive potential energy surfaces and associated inertia. Collective coordinates of &bgr;−&ggr; andq20−q30types are envisaged in this study. Collective states are computed by diagonalizing a collective Hamiltonian whose form is deduced from the Generator Coordinate theory. Well‐localized shape isomers are found in190Hg,192Hg and194Hg at excitation energies 4.4, 5.4, and 6.9 MeV, respectively. Computations of all levels up to spin 22 reveal the existence of three superdeformed bands in192Hg.B(E2)’s for both in‐band and off‐band transitions are obtained. They compare well with available measurements. The decay out of these bands is also discussed. A coupled quadrupole‐octupole collective calculation around the isomer state of192Hg shows that octupole excitations are stiffer than both &bgr; and &ggr; modes.

ISSN:0094-243X    

DOI:10.1063/1.42569

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.42599

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The phenomenon of superdeformed identical bands in both the A=150 and A=190 regions is reviewed. Deviations in the transition energies of the A=190 superdeformed bands at low spins are discussed in terms of variations in the moments of inertia. It is seen that simple blocking arguments predict variations in the static pair correlations at low spins. A simple expression relating the moment of inertia to the pair correlations is then used to extract the relative magnitude of the neutron (proton) pairing within superdeformed configurations. Moreover, low spin differences in the experimental moments of inertia are shown to reflect the predicted differences in the pair correlations.

ISSN:0094-243X    

DOI:10.1063/1.42595

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Coupling schemes which lead to very similar structures in doubly odd, odd and even even nuclei, discovered in the normal‐deformation regime, are reviewed and applied to the problem of identical superdeformed bands. It is shown that such schemes, using as an additional ingredient pseudospin alignment, provide a natural frame to understand this problem.

ISSN:0094-243X    

DOI:10.1063/1.42578

出版商:AIP    

年代:1992

数据来源: AIP