Search for Isovector Valence-Shell Excitations in 140Nd and 142Sm via Coulomb excitation reactions of radioactive ion beams

R D Kern ,J Wiederhold ,J Pakarinen ,K Gladnishki ,L P Gaffney ,G O’neill ,M Scheck ,V Werner ,P Spagnoletti ,J G Cubiss ,C Fransen ,N Warr ,G Rainovski ,A Vogt ,T Kröll ,R Stegmann ,M Djongolov ,O Möller ,A Blazhev ,V Karayonchev ,A Boukhari ,L Kaya ,J Snäll ,D Kocheva ,M Stoyanova ,A Welker ,J Cederkäll ,J Jolie ,H Hess ,H De Witte ,P Reiter ,P.-A Söderström ,S Thiel ,N Pietralla ,J M Keatings ,D Rosiak ,E Giannopoulos ,R Zidarova

doi:10.1051/epjconf/201819403003

Abstract

Projectile Coulomb excitation experiments were performed at HIE-ISOLDE at CERN with the radioactive ion beams of 140Nd and 142Sm. Ions with an energy of 4:62 MeV/A were impinging on a 1.45 mg/cm2 thick 208Pb target. The γ-rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL and scattered particles were detected by a double-sided silicon strip detector. Experimental intensities were used for the determination of electromagnetic transition matrix elements. A preliminary result of the B(M1; 2+3 → 2+1) of 140Nd and an upper limit for the case of 142Sm are revealing the main fragments of the proton-neutron mixed-symmetry 2+1;ms states.

Highlights

The proton-neutron interaction is of particular interest in respect how collectivity emerges in nuclear many-body quantum systems
Projectile Coulomb excitation experiments were performed at HIE-ISOLDE at CERN with the radioactive ion beams of 140Nd and 142Sm
The γ-rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL and scattered particles were detected by a double-sided silicon strip detector

Summary

Introduction

The proton-neutron interaction is of particular interest in respect how collectivity emerges in nuclear many-body quantum systems. The quadrupole-quadrupole part of this interaction forms the lowest-lying collective states in heavy open-shell nuclei. These states have wave functions which are completely symmetric in respect to the exchange of any proton and neutron components. Several cases are reported in the mass A=130 region and recently three cases are found in the mass A=208 region [10,11,12] It is observed, that the even-even N=80 isotones form isolated proton-neutron mixed-symmetry 2+1,ms states from Z=52 to Z=56 [13,14,15]. The configuration of the 2+1,ms state gets more complex and it starts mixing with near-lying 2+ states This effect is called lack of valence-shell stabilization and leads to the suggestion of a proton sub-shell closure at 138Ce (Z=58) [17] for the N=80 isotones.

Analysis and preliminary results

Findings

Summary and Outlook