Neutron knockout from 68,70Ni ground and isomeric states.

F Recchia,S N Liddick,B A Brown,A Korichi,S R Stroberg,R V F Janssens,F G Kondev,S Suchyta,C J Chiara,C Langer,C R Hoffman,J S Berryman,H L Crawford,M P Carpenter,A Gade,E Lunderberg,K Wimmer,J Chen,J A Tostevin,C M Campbell,T Lauritsen,V M Bader,S Noji,M Albers,D Bazin,D Weißhaar ,C J Prokop ,T Baugher,S Zhu

doi:10.1088/1742-6596/966/1/012048

Abstract

Neutron-rich isotopes are an important source of new information on nuclear physics. Specifically, the spin-isospin components in the nucleon-nucleon (NN) interaction, e.g., the proton-neutron tensor force, are expected to modify shell structure in exotic nuclei. These potential changes in the intrinsic shell structure are of fundamental interest. The study of the excitation energy of states corresponding to specific configurations in even-even isotopes, together with the single-particle character of the first excited states of odd-A, neutron-rich Ni isotopes, probes the evolution of the neutron orbitals around the Fermi surface as a function of the neutron number a step forward in the understanding of the region and the nature of the NN interaction at large N/Z ratios.In an experiment carried out at the National Superconducting Cyclotron Laboratory [1], new spectroscopic information was obtained for 68Ni and the distribution of single-particle strengths in 67,69Ni was characterized by means of single-neutron knockout from 68,70Ni secondary beams. The spectroscopic strengths, deduced from the measured partial cross sections to the individual states tagged by their de-exciting gamma rays, is used to identify and quantify configurations that involve neutron excitations across the N = 40 harmonic oscillator shell closure. The de-excitation γ rays were measured with the GRETINA tracking array [2].The results challenge the validity of the most current shell-model Hamiltonians and effective interactions, highlighting shortcomings that cannot yet be explained. These results suggest that our understanding of the low-energy states in such nuclei is not complete and requires further investigation.

Highlights

Nuclear physics aims to understand the properties of nuclei, complex highly-correlated quantum systems, in terms of theoretical models of their structure
With this experiment, it was possible to obtain the precise excitation energy for the 0+2 state in 68Ni, that was correctly predicted by the state-of-the-art shell-model calculations
The new data enabled the identification of a number of new states in both 67Ni and 69Ni, in particular, levels that carry the largest part of the single-particle strength of the neutron orbitals lying at the Fermi surface

Summary

Introduction

Nuclear physics aims to understand the properties of nuclei, complex highly-correlated quantum systems, in terms of theoretical models of their structure. The spectroscopic strengths, deduced from the measured partial cross sections to the individual states tagged by their de-exciting gamma rays, is used to identify and quantify configurations that involve neutron excitations across the N = 40 harmonic oscillator shell closure.

Results

Conclusion