Quadrupole collectivity in the neutron-rich sulfur isotopes S38,40,42,44

Electromagnetic transition strengths in the even-even neutron-rich sulfur isotopes $^{38,40,42,44}\mathrm{S}$ were measured using intermediate-energy Coulomb excitation at the National Superconducting Cyclotron Laboratory. By utilizing the sensitivity of the experimental technique to $E2$ excitations from the ground state, the evolution of the pattern of $B(E2)$ strengths to several low-lying ${2}^{+}$ states was investigated at $Z=16$ from near stability to the $N=28$ island of inversion. The experimental results allowed a detailed comparison with predictions from shell-model calculations using the SDPF-MU Hamiltonian, which was designed to describe collectivity in this region of the nuclear chart. While the shell-model calculations succeeded in modeling transition strengths at $N=22,24,26$, the experimental $B(E2;{0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ at $N=28$ was smaller than the predicted value by about a factor of 2, similar to previous observations for chlorine and argon isotopes around $N=28$. The dependence of this overprediction by theory on the choice of effective charges was explored.