Macroscopic and microscopic description of phase transition in cerium isotopes

The spherical-to-deformed phase transition in cerium isotopes recently suggested to occur between Ce146 and Ce148 has been examined in the framework of the macroscopic algebraic collective model and two microscopic approaches, namely Skyrme-Hartree-Fock + Bardeen-Cooper-Schrieffer (BCS) calculations and the symmetry conserving configuration mixing method with Gogny energy density functionals applied also to the neighboring nuclei along the cerium isotopic chain. Possible spectral signatures of the phase transition are discussed in more details. The microscopic calculations predict octupole softness manifested by rather flat potential energy curves as a function of the octupole deformation parameter β3 for Ce146 and Ce148 and shape coexistence characterized by axially symmetric 0+ states, triaxial 2+ bands, and octupole deformation for the lowest 1- state

New features of the triaxial nuclei described with a coherent state model

Supplementing the Liquid Drop Model (LDM) Hamiltonian, written in the intrinsic reference frame, with a sextic oscillator plus a centrifugal term in the variable $\beta$ and a potential in $\gamma$ with a minimum in $\frac{\pi}{6}$, the Sch\"{o}dinger equation is separated for the two variables which results in having a new description for the triaxial nuclei, called Sextic and Mathieu Approach (SMA). SMA is applied for two non-axial nuclei, $^{180}$Hf and $^{182}$W and results are compared with those yielded by the Coherent State Model (CSM). As the main result of this paper we derive analytically the equations characterizing SMA from a semi-classical treatment of the CSM Hamiltonian. In this manner the potentials in $\beta$ and $\gamma$ variables respectively, show up in a quite natural way which contrasts their ad-hoc choice when SMA emerges from LDM.Comment: 13 figures, 13 page

Intruder bands and configuration mixing in the lead isotopes

A three-configuration mixing calculation is performed in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying $0^+$ states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the Z=82 shell gap.Comment: 20 pages, 4 figures, accepted by PRC, reference added for section 1 in this revised versio

Half-life of the 15/2(+) state of I-135: A test of E2 seniority relations

International audienceThe half-life of the 15/2+1 state of the 3-valence-proton nucleus 135I has been measured to be 1.74(8) ns using the EXILL-FATIMA mixed array of Ge and LaBr3 detectors. The nuclei were produced following the cold neutron-induced fission of a 235U target at the PF1B beam line of the Institut Laue-Langevin. The extracted B(E2;15/2+→11/2+) value enabled a test of seniority relations for the first time between E2 transition rates. Large-scale shell-model calculations were performed for 134Te and 135I, and reinterpreted in a single-orbit approach. The results show that the two-body component of the E2 operator can be large whereas energy shifts due to the three-body component of the effective interaction are small

Algebraic collective model and its applications

International audienceI will review developments and applications of an algebraic version of Bohr’scollective model (BM), known as the algebraic collective model (ACM) withinwhich fully converged calculations can be performed for a range of Hamiltonians.Examining the algebraic structure underlying the BM has clarified itsrelationship with the interacting boson model (IBM), with which it has relatedsolvable limits. I will review results of comparison of the two models for thecase of both axially-symmetric and triaxial rotor. Predictions for single andmulti-phonon excitations of deformed nuclei will be discussed and comparedwith data

Algebraic collective model and nuclear structure applications

International audienc