Unbound states of the neutron-rich oxygen isotopes

The energies of the ground state decay of $^{25}$O and excited states in $^{24}$O were measured for the first time. From these energies the size of the $N = 16$ shell gap may be deduced. Due to the lack of observation of an excited state in $^{24}$O using $\gamma$-ray spectroscopy, along with the known unbound nature of $^{25}$O, techniques involving neutron spectroscopy had to be applied. $^{25}$O ($^{24}$O$^{*}$) was populated via proton (proton-neutron) removal from a $^{26}$F beam. Complete 4-vector reconstruction revealed resonant structures in the decay spectrum for n-$^{22}$O, n-$^{23}$O and n-$^{24}$O coincidence events. From the n-$^{24}$O and n-$^{23}$O decay spectrum the energies of the ground state of $^{25}$O and first excited state of $^{24}$O were measured. Using n-$^{22}$O coincident events of neutron multiplicity $\geq 2$, clear correlation between a low and high energy resonance was observed. With the known placement of the low energy resonance as the first excited state in $^{23}$O, the high energy resonance has been attributed to an excited state in $^{24}$O.