Limits of studying high-spin states by discrete-line gamma-ray spectroscopy

Recent (HI, xn) data on rotational Yb and Hf nuclei are used to describe the motivations and techniques for pushing discrete-line spectroscopy to the realm of the weakly populated yrast and non-yrast states. Three aspects of these studies are discussed: extraction of moments of inertia in different aligned bands, observation and understanding of high-frequency band crossings, and dependence of feeding patterns on nuclear structure

Signature Inversion in Odd-odd Nuclei

Trends in the energy staggering of the {pi}h{sub 11/2}{nu}i{sub 13/2} and {pi}h{sub 11/2} {nu}h{sub 11/2} bands in the mass 160 and 130 regions, respectively, have been investigated in order to better understand the origin of signature inversion. While the A {approx} 160 nuclei behave in a consistent manner, a more complicated scenario is observed in the mass 130 region. As a result of our experiments on the lightest Pr nuclei, the systematics of these Z = 59 nuclei have been extended, which aids in the understanding of the latter region. Triaxial deformation, a pn interaction, and quadrupole pairing are considered as possible contributors to this effect. As all the chiral-twin bands that are known have signature inversion in the favored band, a possible link between the two phenomena should be considered

Restoration of the Broken D2-Symmetry in the Mean Field Description of Rotating Nuclei

Signature effects observed in rotational bands are a consequence of an inherent D2-symmetry. This symmetry is naturally broken by the mean field cranking approximation when a tilted (non-principal) axis orientation of the nuclear spin becomes stable. The possible tunneling forth and back between the two symmetry-related minima in the double-humped potential-energy surface appears as a typical bifurcation of the rotational band. We describe this many-body process in which all nucleons participate by diagonalizing the nuclear Hamiltonian within a selected set of tilted and non-tilted cranking quasiparticle states. This microscopic approach is able to restore the broken D2 symmetry and reproduce the quantum fluctuations between symmetry- related HFB states which emerge as splitting of the band energies and in parallel staggering in intraband M1 transitions.Comment: 9 pages, 4 figure

Signature inversion in axially deformed 160,162^{160,162}Tm

The microscopic analysis of experimental data in $^{160,162}$Tm is presented within the two-quasiparticle-phonon model. The model includes the interaction between odd quasiparticles and their coupling with core vibrations. The coupling explains naturally the attenuation of the Coriolis interaction in rotating odd-odd nuclei. It is shown that the competition between the Coriolis and neutron-proton interactions is responsible for the signature inversion phenomenon.Comment: 10 pages, 1 figure, corrected some typo

Varied Signature Splitting Phenomena in Odd Proton Nuclei

Varied signature splitting phenomena in odd proton rare earth nuclei are investigated. Signature splitting as functions of $K$ and $j$ in the angular momentum projection theory is explicitly shown and compared with those of the particle rotor model. The observed deviations from these rules are due to the band mixings. The recently measured $^{169}$Ta high spin data are taken as a typical example where fruitful information about signature effects can be extracted. Six bands, two of which have not yet been observed, were calculated and discussed in detail in this paper. The experimentally unknown band head energies are given

Superdeformed bands in 189Tl

Two superdeformed bands of 10 transitions each have been found in 189Tl extending the mass 190 region of superdeformation down to neutron number N5108. The new bands can be interpreted as signature partners and are proposed to be based on a proton i13/2 (V55/2) configuration, in analogy with the yrast superdeformed band structures in the heavier odd-mass Tl isotopes. The dynamic moments of inertia of all these bands show no noticeable differences as function of N, consistent with an essentially constant quadrupole deformation from the center of the island to its edges

Level structures of 96,97,98Ru at high angular momentum

The high-spin level structures of 96,97,98Ru (Z544) have been investigated using the 65Cu(36S, pxn)96,97,98Ru (x54,3,2) reactions. About 130 new transitions have been observed and unambiguously placed in the decay schemes of these nuclei. The level schemes have been extended up to spin J'22– 34\, and excitation energies Ex'20224 MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using 88Sr as the core give a reasonable agreement for the observed energy levels up to J16\), possibly manifesting vibrational behavior

Level structure of 94,95,96Tc at high spins and shell-model calculations

High-spin states in the 94,95,96Tc (N = 51, 52, and 53) nuclei have been investigated using the 65Cu+H36S reaction at a beam energy of 142 MeV. More than 60 new transitions have been identified and placed in their level schemes, which now extend up to spin J ≈ 22ℏ and excitation energies Ex ≈ 12 MeV. Spherical shell-model calculations have been performed using different model spaces. A restricted model space, using 88Sr as the core and the π(p 1/2,g9/2) ν(d5/2,s1/2) valence orbitals, reproduces the experimental excitation energies up to J ≈ 14ℏ. The higher-angular-momentum states are dominated by the excitation of a g9/2 neutron across the N = 50 magic core, as indicated by large-basis shell model calculations

Nuclear structure of 94,95Mo at high spins

The high-spin level structures of 94,95Mo (N552,53) have been investigated via the 65Cu(36S, a p2n)94Mo and 65Cu(36S, a pn)95Mo reactions at 142 MeV. The level schemes have been extended up to spin J'19\ and excitation energies Ex'12 MeV. Spherical shell-model calculations have been performed and compared with the experimental energy levels. The level structure of 94Mo exhibits a single-particle nature and the higher-angular-momentum states are dominated by the excitation of a g9/2 neutron across the N550 shell gap. The level sequences observed in 95Mo have been interpreted on the basis of the spherical shell model and weak coupling of a d5/2 or a g7/2 neutron to the 94Mo core

High-spin states in 97,98Rh

High-spin states in 97,98Rh (Z545) were populated via the 65Cu( 36S,xn)97,98Rh (x54,3) fusion-evaporation reactions. More than 40 additional transitions have been identified and placed in the decay schemes of these nuclei. The level scheme of 97Rh has been extended up to tentative spins of Jp 539/21,37/22, and the placement of some of the previously known transitions has been revised. The level structure of 97Rh indicates a single-particle nature and the observed levels are reproduced well by spherical shell-model calculations. The level scheme of 98Rh has been extended up to spins J;20\ and up to an excitation energy of ;10 MeV. The low-spin structure of 98Rh (J<10\), appears to indicate also a singleparticle structure, as supported by the stretched coupling scheme @ 97Rh(J8)^n (d5/2)598Rh (J)#