Emerging Nuclear Collectivity: Coulomb Excitation of 106Cd

Nuclear collectivity has traditionally been thought to evolve through stages of seniority, vibrational, and rotational character as one moves from closed to open-shell regions of the nuclear chart. While there are several robust examples of seniority and rotational character, isolating vibrational character has been more difficult, particularly due to the transitional nature between the extremes. The Cd isotopes (Z=48) were long thought of as textbook examples of vibrational nuclei where the low-lying excitation patterns are consistent with such an interpretation. However, this narrative has since been challenged with the ever growing body of nucleon-transfer and electromagnetic matrix element data, showing major discrepancies with the vibrational model. Alternative views now include everything from weakly deformed anharmonic vibrations with double shape coexistence to weakly deformed triaxial rotations with multi shape coexistence. Results from multi-step Coulomb excitation data of 106Cd on 208Pb will be presented and compared to recent interpretations and measurements, including anomalous DSAM-based lifetime values. Excitation of the low-lying states, including two excited 0+ states, was observed in the present study. We report the first measurement of B(E2; 2_1+ -> 0_2+) and B(E2; 2_1+ -> 0_3+), a crucial piece of data for determining the nature of the weak collectivity exhibited in the Cd isotopes. In addition, electric quadrupole moments will be presented for several of the low-lying states. The E2 matrix elements allow the Kumar-Cline sum rules to be applied, giving a model independent measure of deformation on a state-by-state basis. The experiment was performed at the ATLAS facility of Argonne National Laboratory using GRETINA-CHICO2.