26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Search for two-phonon γ-vibrational states in 162Dy through Coulomb excitation

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Nuclear and Particle Physics (NUPP)

Speaker

Tom Perissinotto (The Australian National University)

Description

Until recently, many deformed nuclei have been considered to have excitations described by the collective model of Bohr and Mottelson. However, the interpretation that some states have a collective vibrational character has been challenged to the point that it is necessary to ask whether or not two-phonon excitations exist among the low-energy states of atomic nuclei. In particular, experimental evidence for the characteristic $K^π=0^+,4^+$ two-γ-phonon doublet remains limited.

In the rare-earth region, a $K^π=2^+$ band-head state is commonly observed and can be identified as the single-phonon γ excitation; however, only a small number of candidates for two-phonon γ-vibrational states have been identified. This scarcity, together with the increasing prominence of alternative interpretations for low-lying $K^π=0^+$ states such as shape coexistence and rotations around a triaxial ground state, motivates a re-evaluation of proposed two-phonon assignments and the applicability of the vibrational model in deformed nuclei.

Dysprosium-162 (Z = 66) is one such nucleus, in which states at 1535keV and 2181keV have been interpreted as members of a split $K^π=4^+$ two-phonon γ-vibration configuration. Coulomb excitation provides a sensitive
probe of these structures, selectively populating states via electromagnetic interactions and enabling the extraction of transition strengths. In this work, results from Coulomb-excitation of 162Dy using an 16O beam at the Heavy Ion Accelerator Facility (HIAF) at the Australian National University are presented. This study forms part of a broader experimental program aimed at probing 162Dy with higher-Z beams to enable multi-step Coulomb excitation and direct population of states of interest.

In parallel, the development of a new particle-detector array for the CAESAR system at HIAF is underway. This upgrade is designed to improve particle identification and angular coverage, thereby enhancing the capabilities for future Coulomb-excitation measurements at ANU, with initial experiments planned for later this year.