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

Nuclear structure from direct reactions with rare isotopes: observables, methods and highlights

International audienceAn overview of direct reactions employed for nuclear structure studies is presented. The basicand most used analysis methods of elastic and inelastic scattering, transfer reactions and intermediateenergyremoval reactions are reviewed. The most relevant observables from direct reactions regarding thenuclear many-body problem, as well as related experimental techniques, are illustrated through recentachievements with unstable nuclei

La fermeture de sous-couche N=16

La structure en couches des noyaux riches en neutrons présente des déviations par rapport à celle des noyaux stables. Ces effets de couches pose de fortes contraintes sur les modèles de structure nucléaire. Nous avons étudié la structure nucléaire des isotones N=16 de la stabilité à la drip line neutron, où N=16 est suggéré magique par différents travaux antérieurs. Une étude théorique en champ moyen et au-delà du champ moyen a été effectuée pour caractériser l'évolution avec l'isospin de la fermeture de sous-couche N=16. Ce travail a été réalisé dans un formalisme Hartree-Fock-Bogoliubov avec l'interaction effective de portée finie D1S, en collaboration avec le Service de Physique Nucléaire du CEA-Bruyères-le-Châtel. Afin de cerner l'évolution des orbitales nucléaires responsables du changement de structure des isotones N=16, la réaction de transfert d'un neutron 26Ne(d,p)27Ne en cinématique inverse à 9.7 MeV/u a été réalisée au GANIL (Grand Accélérateur National d'Ions Lourds). Une cible cryogénique de D2 (17 mg.cm^(-2)) a été utilisée au cours de l'expérience. L'utilisation en coïncidence du détecteur de photons EXOGAM et du spectromètre magnétique VAMOS a permis la spectroscopie gamma de 27Ne. Les résultats obtenus suggèrent une réduction du gap entre les couches sd et fp pour les isotones N=17 à mesure que l'on s éloigne de la vallée de stabilité vers la drip line neutron.The sequence of nuclear magic numbers may change from stability to the drip lines. New magic numbers may then appear : we studied the nuclear structure of N=16 isotones from stability to the neutron drip line where N=16 has been suggested to be magic. A systematic study of even-even N=16 nuclei has been achieved at both mean-field and configuration mixing levels using the Gogny D1S effective interaction. These methods allow to investigate single-particle and pairing properties at spherical shape and along axial and triaxial quadrupole deformations, as well as collective properties. The mean-field calculations show that a spherical subshell gap is opening at N=16. The beyond-the-mean-field calculations predict 24O and 22C neutron magic. In order to estimate the structure changes involved in this shell evolution, we performed the gamma spectroscopy of 27Ne using the one neutron transfer reaction 26Ne(d,p)27Ne in inverse kinematics at 9.7 MeV/nucleon at GANIL. A cryogenic D2 target (17 mg.cm^-2) was used during the experiment. The spectroscopy of 27Ne was performed by measuring in coincidence de-excitation gamma rays in EXOGAM with 27Ne ejectiles in the magnetic spectrometer VAMOS. The obtained results suggest a decrease of the negative parity state energies in odd N=17 neutron rich isotones, supporting a reduced sd-fp shell gap in the neutron rich region.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Searching for halo nuclear excited states using sub-coulomb transfer reactions

Through this study we propose to use sub-Coulomb transfer to investigate the one-neutron halo phenomenon within nuclear excited states since this method could naturally guarantee the peripherality of the transfer. Zero-range ADWA calculations are performed with the final nucleus bound under different conditions. It can be observed that there is a clear enhancement of the interaction cross sections when the nucleus is loosely bound within an s orbital.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Probing the density tail of radioactive nuclei with antiprotons

We propose an experiment to determine the proton and neutron content of the radial density tail in short-lived nuclei. The objectives are to (i) to evidence new proton and neutron halos, (ii) to understand the development of neutron skins in medium-mass nuclei, (iii) to provide a new observable that characterises the density tail of short-lived nuclei

Design and characterization of an antiproton deceleration beamline for the PUMA experiment

We report on the design and characterization of an antiproton deceleration beamline, based on a pulsed drift tube, for the PUMA experiment at the Antimatter Factory at CERN. The design has been tailored to high-voltage (100kV) and ultra-high vacuum (below 10−10mbar) conditions. A first operation achieved decelerating antiprotons from an initial energy of 100keV down to (3898±3)eV, marking the initial stage in trapping antiprotons for the PUMA experiment. Employing a high-voltage ramping scheme, the pressure remains below 2×10−10mbar upstream of the pulsed drift tube for 75% of the cycle time. The beamline reached a transmission of (55±3)% for antiprotons decelerated to 4keV. The beam is focused on a position sensitive detector to a spot with horizontal and vertical standard deviations of σhoriz=(3.0±0.1)mm and σvert=(3.8±0.2)mm, respectively. This spot size is within the acceptance of the PUMA Penning trap.We report on the design and characterization of an antiproton deceleration beamline, based on a pulsed drift tube, for the PUMA experiment at the Antimatter Factory at CERN. The design has been tailored to high-voltage (100 kV) and ultra-high vacuum (below $10^{-10}$ mbar) conditions. A first operation achieved decelerating antiprotons from an initial energy of 100 keV down to ($3898\pm 3$) eV, marking the initial stage in trapping antiprotons for the PUMA experiment. Employing a high-voltage ramping scheme, the pressure remains below $2\cdot 10^{-10}$ mbar upstream of the pulsed drift tube for 75% of the cycle time. The beamline reached a transmission of ($55 \pm 3$)% for antiprotons decelerated to 4 keV. The beam is focused on a position sensitive detector to a spot with horizontal and vertical standard deviations of ${\sigma}_\mathrm{horiz}$ = ($3.0 \pm 0.1$) mm and ${\sigma}_\mathrm{vert}$ = ($3.8 \pm 0.2$) mm, respectively. This spot size is within the acceptance of the PUMA Penning trap