Collectivity of Exotic Silicon Isotopes

The determination of the electric quadrupole transition strength between the ground state and first excited state with spin-party of J$^{\pi }$=2$^{+}$ (the B(E2; 0$^{+}\rightarrow$ 2$^{+})$ value) in an even-even nucleus provides a measurement of the low-lying quadrupole collectivity. The B(E2) values for $^{34,36,38,40,42}$Si were measured via intermediate-energy Coulomb excitation at NSCL. The secondary beams were produced by fragmentation of $^{48}$Ca primary beam and guided onto a high-Z target. De-excitation gamma rays indicating the inelastic process were detected around the target position with the high efficiency scintillator array CAESAR in coincidence with scattered projectiles tracked on an event-by-event basis in the S800 spectrograph. The results comprise the first measurements of the quadrupole collectivity of $^{40}$Si and $^{42}$Si and probe the persistence of the $N$=28 magic number. The measured B(E2) values are compared to large-scale shell model calculations and provide insight into the evolution of shell structure and deformation in this region.