Study of the Jacobi shape transition in A≈30 nuclei

Abstract

This paper reports the first observation of the Jacobi shape transition in P31 using high energy γ rays from the decay of giant dipole resonance (GDR) as a probe. The measured GDR spectrum in the decay of P31 shows a distinct low energy component around 10 MeV, which is a clear signature of Coriolis splitting in a highly deformed rotating nucleus. Interestingly, a self-conjugate α-cluster nucleus Si28, populated at similar initial excitation energy and angular momentum, exhibits a vastly different GDR lineshape. Even though the angular momentum of the compound nucleus Si28 is higher than the critical angular momentum required for the Jacobi shape transition, the GDR lineshape is akin to a prolate deformed nucleus. Considering the present results for Si28 and similar observation recently reported in S32, it is proposed that the nuclear orbiting phenomenon exhibited by α-cluster nuclei hinders the Jacobi shape transition. The present experimental results suggest a possibility to investigate the nuclear orbiting phenomenon using high energy γ rays as a probe. © 2018 American Physical Society.