[en] High-spin terminating bands in heavy nuclei were first identified in nuclei around ¹⁵⁸Er₉₀. While examples of special terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work the high-spin structure of ¹⁵⁷Er has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently, four strongly or superdeformed (SD) sequences have been observed in ¹⁷⁴Hf and ultimate cranker calculations predict such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment was run to search for linking transitions between the SD bands and possible wobbling modes

[en] High-spin terminating bands in heavy nuclei were first identified in nuclei around ¹⁵⁸Er₉₀. While examples of terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work, the high-spin structure of ^156,157,158Er has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently four strongly or superdeformed (SD) sequences have been observed in ¹⁷⁴Hf, and cranking calculations using the Ultimate Cranker code predict that such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment took place to search for linking transitions between the SD bands, possible wobbling modes, and new SD band structures

[en] A new frontier of discrete-line γ-ray spectroscopy at ultrahigh spin has been opened in the rare-earth nuclei ^157,158Er. Four rotational structures, displaying high moments of inertia, have been identified, which extend up to spin ∼65(ℎ/2π) and bypass the band-terminating states in these nuclei which occur at ∼45(ℎ/2π). Cranked Nilsson-Strutinsky calculations suggest that these structures arise from well-deformed triaxial configurations that lie in a valley of favored shell energy which also includes the triaxial strongly deformed bands in ^161-167Lu

[en] The ¹¹⁴Cd(⁴⁸Ca,6nγ) reaction at 215 MeV has been investigated using the Gammasphere spectrometer to study the high-spin structure of the nucleus ₆₈¹⁵⁶Er₈₈. Many new transitions have been established along with definitive spin-parity level assignments from a high-fold angular-distribution analysis. In addition, absolute B(M1) and B(E1) strengths have been inferred from measured γ-ray branching ratios. Strong B(E1) strength (10^-3 W.u.) is discussed in terms of possible octupole collectivity at low spin. At high spin, this nucleus undergoes a Coriolis-induced shape transition from a prolate state of collective rotation to a noncollective, triaxial-oblate configuration. The yrast positive-parity structure ultimately terminates in an energetically favored oblate state at I^π=42⁺. Several weak high-energy γ-ray transitions have been discovered that feed this favored state. State-of-the-art cranked Nilsson-Strutinsky calculations are used to interpret the high-spin behavior of ¹⁵⁶Er and comparisons are made with other N=88 isotones.

[en] Two low lying positive-parity bands in ¹³⁰Cs have been examined for chiral signatures. Small energy differences between the two bands, which have been previously observed, have been confirmed and the bands, as well as the number of transitions within and between the bands, extended. The intraband B(M1)/B(E2) ratios and B(M1)_intraband/B(M1)_interband ratios and the energy staggering parameter, S(I), have been deduced for these partner bands. The results are found to be consistent with a chiral interpretation for the two structures. Core-quasiparticle coupling model calculations have been performed to study ¹³⁰Cs assuming a triaxial core. The experimental level energies and electromagnetic properties of the bands, resulting from the πh _11/2 xνh_11/2^-1 configuration, are reasonably well reproduced by the model, providing further evidence in support of the chiral interpretation of the two structures

[en] The Gammasphere spectrometer, in conjunction with the Microball charged-particle array, was used to investigate high-spin states in ¹¹²Te via ⁵⁸Ni(⁵⁸Ni, 4pγ) reactions at 240 and 250 MeV. Several smooth terminating bands were established, and lifetime measurements were performed for the strongest one using the Doppler-shift attenuation method. Results obtained in the spin range 18-32(ℎ/2π) yield a transition quadrupole moment of 4.0±0.5eb, which corresponds to a quadrupole deformation epsilon₂=0.26±0.03; this value is significantly larger than the ground-state deformation of tellurium isotopes. It was also possible to extract a transition quadrupole moment for the yrast band in ¹¹⁴Xe, produced via the 58Ni (58Ni, 2pγ) reaction. A value of 3.0±0.5eb was found in the spin range 16-24(ℎ/2π), which corresponds to a quadrupole deformation epsilon₂=0.19±0.03. Cranked Nilsson-Strutinsky calculations are used to interpret the results

[en] High-spin states have been populated in ₅₂¹¹⁰Te via ⁵⁸Ni(⁵⁸Ni,α2pγ) reactions at 240 and 250 MeV. The Gammasphere γ-ray spectrometer was used in conjunction with the Microball charged-particle detector. The high-spin (I>30) collective level scheme of ¹¹⁰Te, up to ∼45(ℎ/2π), is discussed in this paper. Four new decoupled (ΔI=2) high-spin structures have been observed for the first time, together with two strongly coupled (ΔI=1) bands. These bands all show the characteristics of smooth band termination, and are discussed within the framework of the cranked Nilsson-Strutinsky approach

[en] A lifetime analysis using the Doppler-shift attenuation method has been performed on the Tellurium isotopes ^110,112Te. The experiment was performed using the Gammasphere array in conjunction with the MICROBALL charged-particle detector. Three strongly coupled bands were previously established in ^110,112Te which were observed up to unusually high spins. In the current experiment, it has been possible to extract lifetime measurements using a Doppler broadened lineshape analysis on one of the ΔI=1 band structures in ¹¹⁰Te. In contrast to similar ΔI=1 structures in other nuclei in this mass region, the extracted B(M1) values did not rapidly decrease with increasing angular momentum. Instead, the strongly coupled band in ¹¹⁰Te represents a deformed 1p-1h structure, rather than a weakly deformed structure showing the shears mechanism

[en] The three superdeformed (SD) bands in ¹³²Ce and the two SD bands in ¹³¹Ce have been extended to higher spin following experiments with the EUROBALL IV spectrometer. The two SD bands in ¹³¹Ce have been linked together. However, despite the relatively high population intensity of the bands (up to 5% of the respective channel), it has not been possible to unambiguously link any of the five SD bands into the low-spin, normally deformed structures of ^131,132Ce