Suppressed Electric Quadrupole Collectivity in ${}^{49}$Ti

Abstract

Single-step Coulomb excitation of ${}^{46,48,49,50}$Ti is presented. A complete set of $E2$ matrix elements for the quintuplet of states in ${}^{49}$Ti, centered 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. ${}_{22}^{49}$Ti${}_{27}$ shows a $20\%$ quenching in electric quadrupole transition strength as compared to its semi-magic ${}_{22}^{50}$Ti${}_{28}$ 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 ${}^{49}$Ti-${}^{50}$Ti pair (i.e., approximate single-$j$ $0f_{7/2}$ 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.

8 pages, 5 figures, accepted in Physics Letters B