44 research outputs found
78Ni revealed as a doubly magic stronghold against nuclear deformation
Nuclear magic numbers correspond to fully occupied energy shells of protons or neutrons inside atomic nuclei. Doubly magic nuclei, with magic numbers for both protons and neutrons, are spherical and extremely rare across the nuclear landscape. Although the sequence of magic numbers is well established for stable nuclei, experimental evidence has revealed modifications for nuclei with a large asymmetry between proton and neutron numbers. Here we provide a spectroscopic study of the doubly magic nucleus 78 Ni, which contains fourteen neutrons more than the heaviest stable nickel isotope. We provide direct evidence of its doubly magic nature, which is also predicted by ab initio calculations based on chiral effective-field theory interactions and the quasi-particle random-phase approximation. Our results also indicate the breakdown of the neutron magic number 50 and proton magic number 28 beyond this stronghold, caused by a competing deformed structure. State-of-the-art phenomenological shell-model calculations reproduce this shape coexistence, predicting a rapid transition from spherical to deformed ground states, with 78 Ni as the turning point
Shell structure of the neutron-rich isotopes Co 69,71,73
The structures of the neutron-rich Co69,71,73 isotopes were investigated via (p,2p) knockout reactions at the Radioactive Isotope Beam Factory, RIKEN. Isotopes of interest were studied using the DALI2 Îł-ray detector array combined with the MINOS target and tracker system. Level schemes were reconstructed using the Îł-Îł coincidence technique, with tentative spin-parity assignments based on the measured inclusive and exclusive cross sections. Comparison with shell-model calculations using the Lenzi-Nowacki-Poves-Sieja LNPS and PFSDG-U interactions suggests coexistence of spherical and deformed shapes at low excitation energies in the Co69,71,73 isotopes. The distorted-wave impulse approximation (DWIA) framework was used to calculate the single-particle cross sections. These values were compared with the experimental findings
The COMPASS Experiment at CERN
The COMPASS experiment makes use of the CERN SPS high-intensitymuon and
hadron beams for the investigation of the nucleon spin structure and the
spectroscopy of hadrons. One or more outgoing particles are detected in
coincidence with the incoming muon or hadron. A large polarized target inside a
superconducting solenoid is used for the measurements with the muon beam.
Outgoing particles are detected by a two-stage, large angle and large momentum
range spectrometer. The setup is built using several types of tracking
detectors, according to the expected incident rate, required space resolution
and the solid angle to be covered. Particle identification is achieved using a
RICH counter and both hadron and electromagnetic calorimeters. The setup has
been successfully operated from 2002 onwards using a muon beam. Data with a
hadron beam were also collected in 2004. This article describes the main
features and performances of the spectrometer in 2004; a short summary of the
2006 upgrade is also given.Comment: 84 papes, 74 figure
Spectroscopy of 16B from quasi-free (p,pn) reaction with 17B
Spectroscopy of 16B plays an essential role in understanding the halo structure in 17B, but very limited knowledge has so far been obtained. We have carried out a kinematically complete measurement on the spectroscopy of 16B by using quasi-free (p,pn) reaction on 17B. The level scheme of 16B up to 5 MeV was made clear for the first time
Quasifree Neutron Knockout Reaction Reveals a Small s-Orbital Component in the Borromean Nucleus 17B
International audienceA kinematically complete quasifree (p,pn) experiment in inverse kinematics was performed to study the structure of the Borromean nucleus B17, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 1s1/2 and 0d5/2 orbitals, and a surprisingly small percentage of 9(2)% was determined for 1s1/2. Our finding of such a small 1s1/2 component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B17. The present work gives the smallest s- or p-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of s or p orbitals is not a prerequisite for the occurrence of a neutron halo
Signatures of triaxiality in low-spin spectra of âžâ¶Ge
Low-spin states of neutron-rich âžâŽ,âžâ¶,âžâžGe were measured by in-flight Îł-ray spectroscopy at 270 MeV/u at the RIKEN-RIBF facility. The exotic beams have been produced by primary ÂČÂłâžU in-flight fission reactions and impinged on the MINOS device. MINOS combines a 10-cm long LHâ target with a Time Projection Chamber (TPC) to reconstruct the reaction vertices. The reactions were selected by the BigRIPS and the ZeroDegree spectrometers for the incoming and outgoing channels, respectively. Emitted Îł radiation was detected by the NaI-array DALI2. De-excitations from the 6ââș, 4â,ââș , and 2â,ââș states of âžâŽ,âžâ¶Ge and 4ââș and 2â,ââș states of âžâžGe were observed. The data are compared to state-of-the-art shell model and beyond-mean-field calculations. Furthermore, a candidate for a 3ââș state of âžâ¶Ge was identified. This state plays a key role in the discussion of ground-state triaxiality of âžâ¶Ge, along with other features of the low-energy level scheme. This work was published in [1]
\ensuremath{\gamma}-ray spectroscopy of low-lying yrast and non-yrast states in neutron-rich
International audienceWe report on Îł-ray spectroscopy of low-lying excited states in the neutron-rich Kr94,95,96 isotopes measured as part of the âShell Evolution And Search for Two-plus energies At RIBFâ (SEASTAR) campaign at the RIKEN Radioactive Isotope Beam Factory. Excited yrast and non-yrast states were observed, and half-lives extracted via geant4 simulations. In Kr94,96 candidates for the 31â state were identified. For Kr95, the prompt SEASTAR data were combined with delayed spectroscopic data measured with the EURICA array to observe transitions on top of the known (7/2)+ isomer at a level energy of 195.5(3) keV. The comparison of the new experimental results with five-dimensional collective Hamiltonian (5DCH) and mapped interacting boson model (IBM) calculations, both using the Gogny D1M interaction, could suggest oblate-prolate shape coexistence already in Kr96