Coulomb excitation of superdeformed and non-axial structures in 42Ca

Monday 4 June 2018, 10.00AM

Speaker(s): Kasia Hadynska-Klek from University of Surrey

Superdeformed bands have been in focus of experimental nuclear physics studies for past decades. They have been reported in several regions of the nuclear chart and since then they also have become a new challenge for the nuclear structure theory. Recently, this phenomenon has also been discovered in the A~40 mass region. Unlike in the heavier nuclei, in calcium region the strongly deformed bands are linked to the normal deformed bands with the discreet gamma transitions, suggesting a possible mixing between these structures. Up to now the SD structures have been observed mainly in light-particle scattering and fusion-evaporation reactions, and the known B(E2) values were extracted from the lifetime measurements. However, recently also the Coulomb excitation technique has been hired to populate the SD structures in atomic nuclei.

A dedicated Coulomb excitation experiment aiming to investigate the properties of the superdeformed structure in 42Ca was performed at INFN Laboratori Nazionali di Legnaro in Italy [1,2]. Gamma rays from the Coulomb excited 42Ca beam on 208Pb and 197Au targets were measured by the AGATA HPGe spectrometer in coincidence with back-scattered projectile nuclei detected in the MCP detectors array.

The level of acquired statistics was sufficient to extract a rich set of reduced matrix elements allowing to precisely describe the electromagnetic properties of low-lying yrast and non-yrast states in 42Ca. The quadrupole deformation parameters of the ground state and the side bands in 42Ca were determined from the measured matrix elements. The recently published results, indicating that two structures differing in overall deformation coexist in 42Ca, were compared to state-of-the-art large-scale Shell Model and Beyond Mean Field calculations. In addition, the triaxiality parameter measured for the excited 0+ state provides the first experimental evidence for non-axial character of SD bands in the A~40 mass region.

In this talk I will present the benefits and the challenges of applying the Coulomb excitation method to study highly-deformed structures in atomic nuclei.

[1]  K. Hadyńska-Klęk et al., Phys. Rev. Lett. 117, 062501 (2016) 

[2] K. Hadyńska-Klęk et al., Phys. Rev. C97, 024326 (2018)

Location: P/T 111