Determining the Energy Gap Between the sd-pf Neutron Shells in $^{25}$O

The excited states of $^{25}$O, particularly those of negative parity, are of great interest for determining the evolution of the \emph{sd-pf} shell gap in and around the ``island of inversion.'' Shell Model (WBBS) calculations tuned to nearby $^{27}$Ne predict the 3/2$^{-}$ state in $^{25}$O to be only 500 keV above the ground state, implying the \emph{sd-pf} shell gap to be small. Hence it is likely for nuclei beyond N=16 to have mixing between the 0d$_{3/2}$ and 1p$_{3/2}$ orbitals. A recent experiment, performed at the NSCL, populated $^{25}$O through use of a $(d,p)$ reaction. Using the Ursinus College Liquid Hydrogen Target, an $^{24}$O beam impinged on a deuterium target cell with a thickness of 400 mg/cm$^{2}$ at a rate of approximately 30 pps to produce $^{25}$O, which decayed immediately by neutron emission. The resulting charged fragments were bent by the Sweeper magnet into a suite of charged particle detectors, while the neutrons traveled unimpeded towards MoNA (Modular Neutron Array) and LISA (Large multi-Institutional Scintillator Array). Together, MoNA-LISA and the Sweeper provide a full kinematic measurement from which the decay energy of the 2-body system can be determined. Preliminary results will be discussed.