Gamma Spectroscopy of Nuclei far for Stability

The focus of the present review is the study of neutron-rich medium-mass nuclei around major shells or subshells N=20, 28 or 40. Coulomb excitation of secondary beams and in-beam spectroscopy study using the fragmentation of a stable beam have brought a wealth of informations concerning the behaviour of the closed shells when nuclei contain large neutron excesses. Pionneering experiments in this field are presented with special emphasis on the work achieved at the Ganil accelerator

Shell Evolutions and Nuclear Forces

7 pages, 5 figures, Talk given at the 25th International Nuclear Physics Conference (INPC), Firenze, Italy, 2-7 June 2013International audienceDuring the last 30 years, and more specifically during the last 10 years, many experiments have been carried out worldwide using different techniques to study the shell evolution of nuclei far from stability. What seemed not conceivable some decades ago became rather common: all known magic numbers that are present in the valley of stability disappear far from stability and are replaced by new ones at the drip line. By gathering selected experimental results, beautifully consistent pictures emerge, that very likely take root in the properties of the nuclear forces.The present manuscript describes some of these discoveries and proposes an intuitive understanding of these shell evolutions derived from observations. Extrapolations to yet unstudied regions, as where the explosive r-process nucleosynthesis occurs, are proposed. Some remaining challenges and puzzling questions are also addressed

Beta decay studies of neutron-rich nuclei around N=40

Beta decay studies of neutron-rich nuclei at or around N=40 are presented in the Co, Mn and V isotopic chains aiming to aimig to study excited states in Ni, Fe and Cr isotopes respectively. Examples are taken from experimental studies achieved at Louvain la Neuve, CERN/ISOLDE and GANIL/LISE facilities. Increases in production rates in the last five years has brought a dramatic change in the spectroscopic knowledge in the region of mass when the isospin number is increased. If the spherical N=40 subshell is well-established for 68Ni, its effect is steadily decreased when proceeding towards 64Cr which lies at the mid-distance between Z=20 and Z=28 magic shell

Evolution of the N=50 gap from Z=30 to Z=38 and extrapolation towards 78Ni

The evolution of the N=50 gap is analyzed as a function of the occupation of the proton f5/2 and p3/2 orbits. It is based on experimental atomic masses, using three different methods of one or two-neutron separation energies of ground or isomeric states. We show that the effect of correlations, which is maximized at Z=32 could be misleading with respect to the determination of the size of the shell gap, especially when using the method with two-neutron separation energies. From the methods that are the least perturbed by correlations, we estimate the N=50 spherical shell gap in 78Ni. Whether 78Ni would be a rigid spherical or deformed nucleus is discussed in comparison with other nuclei in which similar nucleon-nucleon forces are at play.Comment: 7 pages, 8 figures, accepted for publication PRC (22 december 2011

Shells and Shapes in the N=28 isotones

International audienceNew experimental results on 43S and 44S reveal that these nuclei are located in a transitional region of shape coexistence between the spherical 48Ca and the oblate 42Si. The origin of the deformation is discussed in terms of the evolution of the single particle energy levels leading to the compression of the energy difference of the orbitals in the sd and pf shells for protons and neutrons, respectively. Therefore, due to quadrupole excitations across the Z = 14 and N = 28 gaps, the intruder configuration in the neutron rich S isotopes became the ground state

Tetrahedral Symmetry in Ground- and Low-Lying States of Exotic A ~ 110 Nuclei

Recent theoretical calculations predict a possible existence of nuclei with tetrahedral symmetry: more precisely, the mean-field hamiltonians of such nuclei are symmetric with respect to double point-group Td. In this paper, we focus on the neutron-rich Zirconium isotopes as an example and present realistic mean-field calculations which predict tetrahedral ground-state configurations in 108,110Zr and low-lying excited states of tetrahedral symmetry in a number of N > 66 isotopes. The motivations for focusing on these nuclei, as well as a discussion of the possible experimental signatures of tetrahedral symmetry are also presented.Comment: Accepted in Phys. Rev. C - Rapid Communication

Low Energy States of 3181Ga50^{81}_{31} Ga_{50} : Elements on the Doubly-Magic Nature of 78^{78}Ni

Excited levels were attributed to $^{81}_{31}$Ga$_{50}$ for the first time which were fed in the $\beta$-decay of its mother nucleus $^{81}$Zn produced in the fission of $^{nat}$U using the ISOL technique. We show that the structure of this nucleus is consistent with that of the less exotic proton-deficient N=50 isotones within the assumption of strong proton Z=28 and neutron N=50 effective shell effects.Comment: 4 pages, REVTeX 4, 5 figures (eps format