Quadrupole collectivity in neutron-rich Cd isotopes

S Bönig ,Thilo Kroll ,S Ilieva ,M Scheck

doi:10.1088/1742-6596/580/1/012023

Abstract

The proximity to the closed shells at Z = 50 and N = 82 makes the neutron-rich Cd isotopes a perfect test case for nuclear theories. The energy of the first excited 2+-state in the even 122-128 shows an irregular behaviour as the Cd isotopes exhibit only a slight increase for 122Cd to 126Cd and even a decrease from 126Cd to 128Cd. This anomaly can so far not be reproduced by shell model calculations. Only beyond mean field calculations with a resultant prolate deformation are capable to describe this anomalous behaviour. In order to gain more information about the neutron-rich Cd isotopes a Coulomb excitation experiment was performed with MINIBALL at REX-ISOLDE, CERN. The extracted transition strengths B (E2,0+gs → 2+1) for 122,124,126,128Cd agree with beyond mean field calculations. The spectroscopic quadrupole moments Qs (2+1) are compared with measurements on odd neutron-rich Cd isotopes.

Highlights

Beyond mean field (BMF) calculations with a resultant prolate deformation agree with the low excitation energy of 124−128Cd [2]
In order to experimentally investigate the evolution of the transition strength in this region, a Coulomb excitation experiment was performed
At REX-ISOLDE (CERN) it became possible to deliver beams of these exotic nuclei such that with the use of the MINIBALL detector array the different theoretical approaches can be tested in this special region

Summary

Introduction

For the investigated Cd nuclei different predictions exist: BMF calculations give a rather high B(E2, 0+gs → 2+1 ) value, SM calculations foresee a much lower strength. In order to experimentally investigate the evolution of the transition strength in this region, a Coulomb excitation experiment was performed. As these nuclei are highly exotic, it is very difficult to produce a beam with a sufficiently high yield to approach the above mentioned quantity. At REX-ISOLDE (CERN) it became possible to deliver beams of these exotic nuclei such that with the use of the MINIBALL detector array the different theoretical approaches can be tested in this special region

Beam and Setup

Contamination and final γ spectrum

Results

Outlook