Coulomb excitation of Sr and the limits of the 40 island of deformation

Russell, R.*; Smallcombe, J. ; 他34名*

Russell, R.*; Smallcombe, J.; 34 of others*

The region of 40 has long been associated with strongly deformed nuclear configurations. The presence of this strong deformation was recently confirmed through lifetime measurements in Sr and Zr nuclei. Theoretically, however, these nuclei present a challenge due to the vast valence space required to incorporate all deformation driving interactions. Recent state-of-the-art predictions indicate a near axial prolate deformation for = and = + 2 nuclei between = = 36 and = = 40. In this work, we investigate the shores of this island of deformation through a sub-barrier Coulomb excitation study of the = + 4 nucleus, Sr. Extracting a spectroscopic quadrupole moment of (2) = 0.5 b, we find that Sr is inconsistent with significant axial prolate deformation with a significance of 1.5. This result, albeit with a large uncertainty, indicates that the predicted region of strong prolate deformation around = = 40 is tightly constrained to the quartet of nuclei: Sr and Zr.