High-Spin Structures in the N = 153 Nucleus 251Cf

In continuation of our exploration of band structures in neutron-rich Cf nuclei using inelastic and transfer reactions, we report new spectroscopic observations in the ²⁵¹Cf nucleus. High-spin states of neutron-rich Cf nuclei were populated using a ²⁰⁸Pb beam from the ATLAS facility at Argonne, incident on a radioactive target mixture of ^{249 , 250 , 251}Cf. Prompt γ rays were detected by the Gammasphere array. Both signatures of the ground state band of ²⁵¹Cf were observed for the first time, with enhanced signal-to-noise achieved through appropriate gates on sum energy and fold parameters. Assignment of the band structure to ²⁵¹Cf is via coincidence with Cf X-rays as well as the excitation of the ²⁰⁸Pb beam partner. Configurations are assigned to the observed band from experimental M1/E2 branching ratios from clean decays within the band. Further data analysis is in progress, and the new results will be discussed in the context of physics of the highest neutron orbitals accessible to spectroscopy in the A = 250 region.

Work supported by U.S. Department of Energy.