In-beam Gamma-ray spectroscopy of 43-46Cl

The low-energy nuclear structure of the neutron-rich $^{43-46}$Cl isotopes is studied via in-beam $\gamma$-ray spectroscopy following the fragmentation of $^{48}$K projectiles on a $^{9}$Be target at intermediate beam energies. $\gamma\gamma$ coincidence information was used to construct level schemes for these neutron-rich nuclei. For the $N=28$ nucleus $^{45}$Cl, the lifetime of the first excited state at 130~keV was extracted via $\gamma$-ray line shape analysis, yielding an $M1$ strength an order of magnitude greater than that predicted by theory. The experimental data is compared to the results of large-scale shell-model calculations with effective interactions in the $sd$-$pf$ model space.