Suppressed electric quadrupole collectivity in ⁴⁹Ti

Abstract

Single-step Coulomb excitation of Ti-46,Ti-48,Ti-49,Ti-50 is presented. A complete set of E2 matrix elements for the quintuplet of states in Ti-49, centred on the 2+ core excitation, was measured for the first time. A total of nine E2 matrix elements are reported, four of which were previously unknown. Ti-49(22)27 shows a 20% quenching in electric quadrupole transition strength as compared to its semi-magic Ti-50(22)28 neighbour. This 20% quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connection to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the Ti-49-Ti-50 pair (i.e., approximate single-j 0f7/2 valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.