The land of deformation south of 68^{68}Ni

We study the development of collectivity in the neutron-rich nuclei around $N=40$, where experimental and theoretical evidences suggest a rapid shape change from the spherical to the rotational regime, in analogy to what happens at the {\it island of inversion} surrounding $^{31}$Na. Theoretical calculations are performed within the interacting shell model framework in a large valence space, based on a $^{48}$Ca core which encompasses the full $pf$ shell for the protons and the $0f_{5/2}$, $1p_{3/2}$, $1p_{1/2}$, $0g_{9/2}$ and $1d_{5/2}$ orbits for the neutrons. The effective interaction is based on a G-matrix obtained from a realistic nucleon-nucleon potential whose monopole part is corrected empirically to produce effective single particle energies compatible with the experimental data. We find a good agreement between the theoretical results and the available experimental data. We predict the onset of deformation at different neutron numbers for the various isotopic chains. The maximum collectivity occurs in the chromium isotopes, where the large deformation regime starts already at $N=38$. The shell evolution responsible for the observed shape changes is discussed in detail, in parallel to the situation in the $N=20$ region

The neutron-rich edge of the nuclear landscape: Experiment and theory

In this review, we describe the experimental facilities and methods which make it possible to produce and measure the properties of the extreme neutron-rich nuclei. We then develop the theoretical framework that predicts and explains these properties; the shell-model approach with large-scale configuration interaction (mixing) SM-CI, with special emphasis in the competition between the spherical mean field and the nuclear correlations (mainly pairing and quadrupole-quadrupole). The SU(3) related symmetry properties of the latter are treated in detail as they will show to be of great heuristic value. We explore the Islands of Inversion (IoI) at N = 20 and N = 28. We make a side excursion into the heavier Calcium and Potassium isotopes, to discuss current issues on shell evolution and new magic numbers far from stability. We revisit the N = 40 Island of Inversion and extrapolate the successful predictions of the LNPS model to 60Ca. We discuss the doubly magic nucleus 78Ni, its shape coexistence and the prospect of a new IoI at N = 50 below Z = 28. Finally, we examine the behaviour of the N = 70 and N = 82 neutron closures as the neutron drip line is approachedAP’s work is supported in part by the Ministerio de Ciencia, Innovación y Universidades (Spain), Severo Ochoa Programme SEV-2016-0597 and grant PGC-2018-94583. AO acknowledges the support by the Alexander von Humboldt foundation and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project-ID 279384907 - SFB 124

Novel nuclear structure aspects of the Oνββ-decay

We explore the influence of the deformation on the nuclear matrix elements of the neutrinoless double beta decay (NME), concluding that the difference in deformation -or more generally in the amount of quadrupole correlations- between parent and grand daughter nuclei quenches strongly the decay. We correlate these differences with the seniority structure of the nuclear wave functions. In this context, we examine the present discrepancies between the NME's obtained in the framework of the Interacting Shell Model and the Quasiparticle RPA. In our view, part of the discrepancy can be due to the limitations of the spherical QRPA in treating nuclei which have strong quadrupole correlations. We surmise that the NME's in a basis of generalized seniority are approximately model independent, i. e. they are "universal"This work is partly supported by the Spanish Ministry of Ciencia e Innovación under grant FPA2009-13377, by the Comunidad de Madrid (Spain) project HEPHACOS S2009/ESP-1473, by the IN2P3(France)-CICyT(Spain) collaboration agreements, by the DFG through grant SFB 634 [J.M.], and by the Helmholtz Association through the Helmholtz Alliance Program, contract HA216/EMMI “Extremes of Density and Temperature: Cosmic Matter in the Laboratory” [J.M.

Neutrinoless double beta decay the nuclear matrix elements revisited

We explore the influence of the deformation on the nuclear matrix elements of the neutrinoless double beta decay (NME), concluding that the difference in deformation -or more generally in the amount of quadrupole correlations- between parent and grand daughter nuclei quenches strongly the decay. We correlate these differences with the seniority structure of the nuclear wave functions. In this context, we examine the present discrepancies between the NME's obtained in the framework of the Interacting Shell Model and the Quasiparticle RPA. In our view, part of the discrepancy can be due to the limitations of the spherical QRPA in treating nuclei which have strong quadrupole correlations. We surmise that the NME's in a basis of generalized seniority are approximately model independent, i. e. they are "universal". We discuss as well how varies the nuclear matrix element of the 76Ge decay when the wave functions of the two nuclei involved in the transition are constrained to reproduce the experimental occupancies. In the Interacting Shell Model description the value of the NME is enhanced about 15% compared to previous calculations, whereas in the QRPA the NME's are reduced by 20%-30%. This diminishes the discrepancies between both approaches. In addition, we update the effects of the short range correlations on the NME's in the light of the recently proposed parametrizations obtained by renormalizing the 0νββ transition operator at the same footing than the effective interactionThis work is partly supported by the Spanish Ministry of Ciencia e Innovación under grant FPA2009-13377, by the Comunidad de Madrid (Spain) project HEPHACOS S2009/ESP-1473, by the IN2P3(France)-CICyT(Spain) collaboration agreements, by the DFG through grant SFB 634 [J.M.], and by the Helmholtz Association through the Helmholtz Alliance Program, contract HA216/EMMI “Extremes of Density and Temperature: Cosmic Matter in the Laboratory”[J.M.

Spectroscopy of odd-mass cobalt isotopes toward the N=40 subshell closure and shell-model description of spherical and deformed states

The neutron-rich cobalt isotopes up to A = 67 have been studied through multinucleon transfer reactions by bombarding a 238U target with a 460-MeV 70Zn beam. Unambiguous identification of prompt γ rays belonging to each nucleus has been achieved using coincidence relationships with the ions detected in a high-acceptance magnetic spectrometer. The new data are discussed in terms of the systematics of the cobalt isotopes and interpreted with large-scale shell-model calculations in the fpgd model space. In particular, very different shapes can be described in 67Co, at the edge of the island of inversion at N = 40, where a low-lying highly deformed band coexists with a spherical structureThis work was partially supported by the European Community FP6, Structuring the ERA Integrated Infrastructure Initiative Contract No. EURONS RII3-CT-2004-506065, by MICINN, Spain (Contract No. FPA2011-29854), by IN2P3, France (Contract No. AIC-D-2011-648), by Comunidad de Madrid, Spain (Contract No. HEPHACOS S2009-ESP-1473), and by Generalitat Valenciana, Spain (Contract No. PROMETEO/ 2010/101). A. Gadea and E. Farnea acknowledge the support of MICINN, Spain, and INFN, Italy, through the AIC-D-2011-0746 bilateral actio

First signs of collectivity in N = 86 and 88 isotones above 132Sn

Within the shell-model framework the low-lying states energies, E2 and M1 transitions of chains of nuclei 52 ≤ Z ≤ 60 with 82 ≤ N ≤ 88 are investigated. We use the N3LOP effective interaction derived from Effective Field Theory Potentials and phenomenologically constrained. We noticed clear collective features in N = 86 and 88 isotones, with signature of triaxial γ-bands

Spectroscopic Properties and Collectivity Beyond 132^{132}Sn

International audienceRecent shell-model advances in the mass region above the doubly closed core 132Sn are reported in the present work. Using an effective interaction based on the N3LO potential, the low-lying spectra, E2 and M1 transition strengths are calculated for the following nuclei: 134,136,138Te, 136,138,140Xe, 138,140,142Ba, 140,142,144Ce and 142,144,146Nd. We focus in the discussion on the collectivity in the N = 86 isotones characterized by development of triaxial γ bands

First signs of collectivity in

Within the shell-model framework the low-lying states energies, E2 and M1 transitions of chains of nuclei 52 ≤ Z ≤ 60 with 82 ≤ N ≤ 88 are investigated. We use the N3LOP effective interaction derived from Effective Field Theory Potentials and phenomenologically constrained. We noticed clear collective features in N = 86 and 88 isotones, with signature of triaxial γ-bands