γ -soft Ba 146 and the role of nonaxial shapes at N≈90

Low-spin states in the neutron-rich, N=90 nuclide Ba146 were populated following β decay of Cs146, with the goal of clarifying the development of deformation in barium isotopes through delineation of their nonyrast structures. Fission fragments of Cs146 were extracted from a 1.7-Ci Cf252 source and mass selected using the CAlifornium Rare Ion Breeder Upgrade (CARIBU) facility. Low-energy ions were deposited at the center of a box of thin β detectors, surrounded by a highly efficient high-purity Ge array. The new Ba146 decay scheme now contains 31 excited levels extending up to ∼2.5 MeV excitation energy, double what was previously known. These data are compared to predictions from the interacting boson approximation (IBA) model. It appears that the abrupt shape change found at N=90 in Sm and Gd is much more gradual in Ba and Ce, due to an enhanced role of the γ degree of freedom

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First-excited state g factors in the stable, even Ge and Se isotopes FIRST-EXCITED STATE g FACTORS in the ... B. P. McCORMICK et al.

International audienceTransient-field $g$-factor measurements in inverse kinematics were performed for the first-excited states of the stable, even isotopes of Ge and Se. The $g$ factors of $^{74}$Ge and $^{74}$Se were measured simultaneously using a cocktail beam, which eliminates most possible sources of systematic error in a relative $g$-factor measurement. The results are $g(^{74}{\rm Se})/g(^{74}{\rm Ge})=1.34(7)$, $g(^{70}{\rm Ge})/g(^{74}{\rm Ge}) = 1.16(15)$, $g(^{72}{\rm Ge})/g(^{74}{\rm Ge})=0.92(13)$, $g(^{76}{\rm Ge})/g(^{74}{\rm Ge})=0.88(5)$, $g(^{76}{\rm Se})/g(^{74}{\rm Se})=0.96(7)$, $g(^{78}{\rm Se})/g(^{74}{\rm Se})=0.82(5)$, $g(^{80}{\rm Se})/g(^{74}{\rm Se})=0.99(7)$ and $g(^{82}{\rm Se})/g(^{74}{\rm Se})=1.19(6)$. The measured $g$-factor ratios are in agreement with ratios from previous measurements, despite considerable variation in previous reported absolute values. The absolute values of the $g$ factors remain uncertain, however the Rutgers parametrization was used to set the transient-field strength and then compare the experimental $g$ factors with shell-model calculations based on the JUN45 and jj44b interactions. Modest agreement was found between experiment and theory for both interactions. The shell model calculations indicate that the $g(2^+_1)$ values and trends are determined largely by the balance of the spin carried by orbital motion of the protons

γ{\gamma}-ray spectroscopy of a four-quasiparticle isomer band in 174Re^{174}Re

Excited states in Re174 have been populated in fusion-evaporation reactions at the Australian National University, and γ-ray spectroscopy has been used to determine the level structure and to deduce the underlying nucleon configurations. The half-life of the bandhead of the Kπ=8- band has been measured to be 2.7(4) ns. A band built on an isomeric state of spin-parity (14-) and a half-life of 53(5) ns has been observed here for the first time, and has been determined to have a four-quasiparticle structure. Contrasting reduced-hindrance values for its decay are discussed in terms of deformation and configuration changes, as indicated by configuration-constrained potential energy surface calculations