Evidence for octupole collectivity in ^{172}{mathrm {Pt}}

A Ertoprak,R J Liotta ,B S Nara Singh ,M Giles,E Ganioğlu ,D M Cullen,M Nyman,T Grahn,E S Paul,M Doncel,J Partanen,S Matta,P Jones ,Y Fang ,P Rahkila,B Hadinia,C Scholey,U Jakobsson,J Uusitalo,J Sorri,Chong Qi ,C M Petrache,S Stolze,M Nııkura ,V Modamio,A Johnson,İlker Özgür ,T Braunroth,K Andgren,P Peura,P Ruotsalainen,P Papadakis,M Leino,J Sarén,B Cederwall,S Ketelhut,R Wyss,M Kumar Raju ,J Pakarinen,D Hodge,P Subramaniam,Hailong Li ,D M Cox,E Ideguchi,J Hilton,R D Page,S Juutinen,R Julin,J J Valiente-Dobón,T Calverley,A Khaplanov,T Bäck,M B Gómez Hornillos ,M Sandzelius,M J Taylor,H Liu,Ö Aktaş ,P T Greenlees,H Badran

doi:10.1140/epja/s10050-020-00071-6

Abstract

Excited states in the extremely neutron-deficient nucleus ^{172}{mathrm {Pt}} were populated via ^{96}mathrm {Ru}(^{78}mathrm {Kr},2p) and ^{92}mathrm {Mo}(^{83}mathrm {Kr},3n) reactions. The level scheme has been extended up to an excitation energy of approx 5~hbox {MeV} and tentative spin-parity assignments up to I^pi = 18^+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3^-. In addition, we observed an E3 transition from this 3^- state to the ground state, providing direct evidence for octupole collectivity in ^{172}{mathrm {Pt}}. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3^- state as a collective octupole-vibrational state.

Highlights

The concept of deformations and shapes in atomic nuclei, based on the observations of large quadrupole moments, rotational band structures and vibrational-like spectra is one of the corner stones of nuclear physics
A reasonable agreement between experiment and theory is obtained for the relative excitation energies of the yrast and near-yrast states with the notable exception of the 3− state, which is experimentally observed to be situated much lower in excitation energy relative to the low-lying yrast positive-parity states compared with the Large-scale shell model (LSSM) prediction
We report the observation of new excited states in 172Pt, extending information on its structure compared with previous studies

Summary

Introduction

The concept of deformations and shapes in atomic nuclei, based on the observations of large quadrupole moments, rotational band structures and vibrational-like spectra is one of the corner stones of nuclear physics. Most deformed nuclei seem adequately described by an axial- and reflectionsymmetric prolate spheroidal shape, and due to its invariance under space inversion, all members of rotational band structures based on it will have the same parity [1]. Deviations from this simple picture, like oblate, triaxial, or higher-order multipole shapes appear, surprisingly, to be quite rare. Ample experimental evidence such as interleaved positive- and negativeparity states, large electric dipole and octupole moments, and

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Experimental details

Data analysis

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Discussion

Summary