First spectroscopy of 61Ti and the transition to the Island of Inversion at N = 40

K Wimmer,F Recchia,D Kahl,H Schaffner,V Werner,C Stahl,I Kojouharov,N Kurz,M Labiche,S Riccetto,F Nowacki,P Schrock,G Kiss,Soo-Jin Choi ,H Sakuraï ,S M Lenzi ,P Doornenbal,T Sumikama,William Edward Witt ,S Bae,S Nishimura,V H Phong ,T Isobe,P R John ,M Nııkura ,Yoshihiko Saito ,H Baba,Muneerah A Alaqeel ,D R Napoli ,S Momiyama,T Davinson,C R Niţă ,Takashi Ando ,C J Griffin ,A Estradé ,A Poves,Ö Aktaş ,P.-A Söderström,L J Harkness-Brennan ,J H Ha ,K Matsui,P J Woods

doi:10.1016/j.physletb.2019.03.018

Abstract

Isomeric states in 59,61Ti have been populated in the projectile fragmentation of a 345 AMeV 238U beam at the Radioactive Isotope Beam Factory. The decay lifetimes and delayed γ-ray transitions were measured with the EURICA array. Besides the known isomeric state in 59Ti, two isomeric states in 61Ti are observed for the first time. Based on the measured lifetimes, transition multipolarities as well as tentative spins and parities are assigned. Large-scale shell model calculations based on the modified LNPS interaction show that both 59Ti and 61Ti belong to the Island of Inversion at N=40 with ground state configurations dominated by particle-hole excitations to the g9/2 and d5/2 orbits.

Highlights

The study of nuclei far off stability in regions that have not yet been explored – and in particular its description in terms of nuclear shell structure – is fundamental in order to obtain predictive capabilities and to be able to understand the relevant characteristics of such nuclei
The present data have been interpreted in the framework of the large-scale shell model calculations using the LNPS interaction [4]
The model space consists of the full p f shell for protons and the 1 f5/2, 2p3/2, 2p1/2, 1g9/2, and 2d5/2 neutron orbitals outside a 48Ca core

Summary

Introduction

The study of nuclei far off stability in regions that have not yet been explored – and in particular its description in terms of nuclear shell structure – is fundamental in order to obtain predictive capabilities and to be able to understand the relevant characteristics of such nuclei. Due to enormous computational advancements in the recent years and the development of new interactions, the shell model is able to predict the structure of nuclei far from closed shells. One example of this are the neutron-rich N = 40 nuclei below 68Ni ( Z = 28). By removing a few protons, a rapid increase of collectivity has been observed in the Fe and Cr isotopes, suggesting a weakening of the N = 40 sub-shell closure [2,3] This collective behavior is caused by quadrupole correlations which energetically favor the deformed intruder states involving the neutron 1g9/2 and 2d5/2 orbitals and proton excitations across the Z = 28 sub-shell gap.

Methods

Results

Conclusion