Spectroscopy of [formula omitted]Mn: Strong coupling in the N = 40 “island of inversion”

X.Y Liu,A Peyaud,T Uesaka,S Koyama,R Taniuchi,D Suzuki,V Lapoux,W.Q Zhang,G Authelet,S Franchoo,A Corsi,Zs Vajta,S Momiyama,V Werner,T Sumikama,L Olivier,K Matsui,K Yoneda,D Calvet,A Delbart,D Steppenbeck,Z Patel,A Gottardo,J Wu,C Shand,M Sasano,P Doornenbal,F.S Zhang,Y.H Zhang,H Otsu,Z Liu,M Lettmann,S Nishimura,M Matsushita,C Santamaria,T Motobayashi,F Giacoppo,T Isobe,F Château,Z Korkulu,F Nowacki,A Obertelli,C Louchart,A Gillibert,F Browne,S Ota,J Lee,J.-Y Roussé,J.-M Gheller,H Baba,P.-A Söderström,R Lozeva,P M Walker ,Mingze Sun ,Handing Wang ,Z Y Xu ,Satoshi Takeuchi ,Takamichi Miyazaki ,Clara Péron ,S M Lenzi ,M Nııkura ,E Šahin ,G L Stefan ,Zs Dombrádi ,T H Huang ,D S Hou ,Hui Xu ,L X Chung ,Y H Lam ,E Pollacco ,B D Linh ,Haiyang Lu ,Yoshinori Shiga ,K Hadyńska-Klȩk ,Yuki Kubota ,H Sakuraï ,Xianming Zhou ,Bing Ding

doi:10.1016/j.physletb.2018.06.067

Abstract

Excited states in 63,65,67Mn were studied via in-beam γ-ray spectroscopy following knockout reactions from 68Fe. Similar level schemes, consisting of the 11/2−, 9/2−, 7/2− and 5/2g.s.− level sequence, connected by I→I−1 transitions, were established, the first time for 65,67Mn. Their level structures show features consistent with strongly-coupled rotational bands with K=5/2. State-of-the-art shell-model calculations with the modified LNPS effective interaction reproduce the observed levels remarkably well and suggest the dominance of 4-particle-4-hole neutron configurations for all the states. The data on the low-lying excited states of odd-mass 53−67Mn provide a textbook example of nuclear structure evolution from weak coupling through decoupling to strong coupling along a single isotopic chain on the n-rich side of the β stability line. These results help to deepen our understanding of the N=40 “island of inversion”.

Highlights

With the acquisition of experimental data on nuclei far from stability in the last decades, the paradigm of universal shell structure has been abandoned [1,2], and much progress has been made by investigating the mechanism of shell evolution
The experiment was performed at the Radioactive Isotope Beam Factory (RIBF), operated by the RIKEN Nishina Center and the Center for Nuclear Study of the University of Tokyo
As for 63Mn, a transitional feature between decoupling and strong coupling is reflected in the slight departure from the linear relation in excitation energy

Summary

Introduction

With the acquisition of experimental data on nuclei far from stability in the last decades, the paradigm of universal shell structure has been abandoned [1,2], and much progress has been made by investigating the mechanism of shell evolution. While its ground state is still dominated by the normal f p configuration of a spherical shape [8,9,10], well deformed structures that become the ground state of lighter N ∼ 40 nuclei have been observed recently, especially in Fe and Cr isotopes [11,12,13,14,15,16,17]. Compared with the relatively simple response of eveneven nuclei to the development of collectivity, e.g., the decrease of the 2+1 energy and the increase of the E(4+1 )/E(2+1 ) ratio, the level structure of an odd-mass nucleus is sensitive to both the deformation of the underlying even-even core and the configuration of the unpaired nucleon [23]. As key isotopes in Urca cycle that cools the neutron star crusts via neutrino cooling [34], information on the low-lying levels of 63,65Mn are of importance in deducing the electron capture and β-decay rates for the 63Fe ↔ 63Mn and 65Fe ↔ 65Mn Urca pairs [34]

Experiment and results

Discussion

Conclusion