Solving nuclear shape conundrum at HIE-ISOLDE

Abstract

It is the purpose of this paper to illustrate some of the low-energy nuclear physics that we want to pursue at the new HIE-ISOLDE radioactive-ion-beam facility at CERN. The University of the Western Cape leads an experimental proposal and co-authors two Letters of Intent, in collaboration with European institutions, at HIE-ISOLDE. Timely topics such as the "Exploration of K-isomerism using unique high-K isomeric beams – CERN-INTC-I-101" and "Shape changes and proton-neutron pairing around the N = Z line – CERN-INTC-I-102" are addressed in these Letters of Intent. Our experimental proposal aims at performing a multi-step Coulomb-excitation of radioactive 70Se ion beams using the 208Pb(70Se,70Se*)208Pb* reaction at a bombarding energy of 5.5 MeV/u. The physics goal is a precise measurement of the (2+1 || Ê2 || 2+1) diagonal matrix element, related to the spectroscopic quadrupole moment, in 70Se. Full simulations presented in this work show distinct angular distributions for plausible values of the spectroscopic quadrupole moment; with a predicted uncertainty of approximately ±0.1 eb. Additional diagonal and transitional matrix elements will also be obtained. These results will shed light onto the origin of rarely-found oblate shapes and shape coexistence in this region of rapidly-changing shell structure.