Nuclear structure studies of 254Es region by Coulomb excitation gamma-ray spectroscopy*

What is the limit of high Z nucleus, where is the island of stability, is one of the focus of nuclear
physics. Key ingredient to stabilize nucleus in this super-heavy region is shell structure and Z=114,120, N=184 are predicted to be new magic numbers. However, it is not easy to produce such nucleus and study the shell structure.

In order to access such shell structure, we are focusing on the deformed nucleus of the heavy mass region including Es isotopes. By studying the excited states, spin and parity, and deformation, we will be able to access the single-particle orbital which is supposed to generate new shell structure at Z=114, 120, N=184 and try to investigate nuclear shell structure in the super-heavy mass region.

Coulomb excitation experiment at the Tokai Tandem Accelerator Laboratory of JAEA is planned to measure B(E2) values of low-lying states in ²⁵⁴Es and to deduce the deformation. Unknown high-lying states of ²⁵⁴Es will be also investigated for further understanding of nuclear structure in this region. We obtained ²⁵⁴Es via an international collaboration with ORNL. CAGRA will be used to measure the gamma rays from ²⁵⁴Es. 

Experimental plan and preparation progress will be presented.