Abstract
The first high-resolution in-beam γ -ray spectroscopy is reported for the neutron-rich nucleus 41Si, a tenant of the N = 28 island of inversion. Excited states were populated in the direct one-proton removal reaction from 42P projectiles and pn removal from 43P. Seven γ -ray transitions were observed, only one of which had been reported previously in the literature. This makes 41Si the most neutron-rich odd-even N = 27 isotone with high-resolution excited-state information. For the one-proton removal, the measured partial cross-section distribution to all observed bound final states is contrasted with results from direct one-proton removal calculations that combine eikonal reaction dynamics with SDPF-MU shell-model spectroscopic factors and assume various possible initial states for the poorly known 42P projectile. Rather distinct calculated cross-section distributions emerge that, in comparison to the new data, imply that the initial state in 42P is most likely 3− or 2− rather than 1− or 0−, the predicted shell-model ground state of 42P. It is further shown that the level scheme from the novel VS-IMSRG calculation closely agrees with the one of SDPF-MU, the most successful phenomenological shell-model effective interaction in describing the much discussed neighboring isotope 42Si, perhaps cross-validating these complementary approaches on the quest to model rapid shell evolution away from the valley of β stability.