In-beam spectroscopy of medium- and high-spin states in 133^{133}Ce

Medium and high-spin states in $^{133}$Ce were investigated using the $^{116}$Cd($^{22}$Ne, $5n$) reaction and the Gammasphere array. The level scheme was extended up to an excitation energy of $\sim22.8$ MeV and spin 93/2 . Eleven bands of quadrupole transitions and two new dipole bands are identified. The connections to low-lying states of the previously known, high-spin triaxial bands were firmly established, thus fixing the excitation energy and, in many cases, the spin parity of the levels. Based on comparisons with cranked Nilsson-Strutinsky calculations and tilted axis cranking covariant density functional theory, it is shown that all observed bands are characterized by pronounced triaxiality. Competing multiquasiparticle configurations are found to contribute to a rich variety of collective phenomena in this nucleus.Comment: 20 pages, 11 figure

Evidence for Multiple Chiral Doublet Bands in 133^{133}Ce

Two distinct sets of chiral-partner bands have been identified in the nucleus $^{133}$Ce. They constitute a multiple chiral doublet (M$\chi$D), a phenomenon predicted by relativistic mean field (RMF) calculations and observed experimentally here for the first time. The properties of these chiral bands are in good agreement with results of calculations based on a combination of the constrained triaxial RMF theory and the particle-rotor model.Comment: Minor changes based on referee reviews and corrections of some typo

From chiral vibration to static chirality in ^{135}Nd

Electromagnetic transition probabilities have been measured for the intra- and inter-band transitions in the two sequences in the nucleus ^{135}Nd that were previously identified as a composite chiral pair of rotational bands. The measurements are in good agreement with results of a new combination of TAC and RPA calculations. The chiral character of the bands is affirmed and it is shown that their behavior is associated with a transition from a vibrational into a static chiral regime.Comment: Accepted for publication in the Physical Review Letters. Small modifications to fit the length limits of the journal. 10 pages, 4 figure

Evidence for Shape Co-existence at medium spin in 76Rb

Four previously known rotational bands in 76Rb have been extended to moderate spins using the Gammasphere and Microball gamma ray and charged particle detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g9/2 particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters

Nature of yrast excitations near N=40: Level structure of Ni-67

Excited states in Ni-67 were populated in deep-inelastic reactions of a Ni-64 beam at 430 MeV on a thick U-238 target. A level scheme built on the previously known 13 micro-s isomer has been delineated up to an excitation energy of ~5.3 MeV and a tentative spin and parity of (21/2-). Shell model calculations have been carried out using two effective interactions in the f5/2pg9/2 model space with a Ni-56 core. Satisfactory agreement between experiment and theory is achieved for the measured transition energies and branching ratios. The calculations indicate that the yrast states are associated with rather complex configurations, herewith demonstrating the relative weakness of the N=40 subshell gap and the importance of multi particle-hole excitations involving the g9/2 neutron orbital.Comment: Accepted by Physical Review

Influence of nuclear structure on sub-barrier hindrance in Ni+Ni fusion

Fusion-evaporation cross sections for $^{64}$Ni+$^{64}$Ni have been measured down to the 10 nb level. For fusion between two open-shell nuclei, this is the first observation of a maximum in the $S$-factor, which signals a strong sub-barrier hindrance. A comparison with the $^{58}$Ni+$^{58}$Ni, $^{58}$Ni+$^{60}$Ni, and $^{58}$Ni+$^{64}$Ni systems indicates a strong dependence of the energy where the hindrance occurs on the stiffness of the interacting nuclei.Comment: Submitted to Phys. Rev. Lett. 4 pages, 3 figure