The structure of ${}^{33}\mathrm{Si}$ was studied by a one-neutron knockout reaction from a ${}^{34}\mathrm{Si}$ beam at 98.5 MeV/u incident on a ${}^9\mathrm{Be}$ target. The prompt $\gamma$ rays following the de-excitation of ${}^{33}\mathrm{Si}$ were detected using the GRETINA $\gamma$-ray tracking array while the reaction residues were identified on an event-by-event basis in the focal plane of the S800 spectrometer at the National Superconducting Cyclotron Laboratory. The presently derived spectroscopic factor values, $C^{2}S$, for the $3/2^{+}$ and $1/2^{+}$ states, corresponding to a neutron removal from the $0d_{3/2}$ and $1s_{1/2}$ orbitals, agree with shell model calculations and point to a strong $N=20$ shell closure. Three states arising from the more bound $0d_{5/2}$ orbital are proposed, one of which is unbound by about 930 keV. The sensitivity of this experiment has also confirmed a weak population of $9/2^{-}$ and $11/2_{1,2}^{-}$ final states, which originate from a higher-order process. This mechanism may also have populated, to some fraction, the $3/2^{-}$ and $7/2^{-}$ negative-parity states, which hinders a determination of the $C^{2}S$ values for knockout from the normally unoccupied $1p_{3/2}$ and $0f_{7/2}$ orbits.

• Received 11 March 2020
• Revised 3 June 2020
• Accepted 29 July 2020

DOI:https://doi.org/10.1103/PhysRevC.102.024321