Shell Structure of the Near-Dripline Nucleus ${}^{23}\mathrm{O}$

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope ${}^{23}\mathrm{O}$. The ${}^{22}\mathrm{O}$ fragments produced in one-nucleon removal from ${}^{23}\mathrm{O}$ at $938\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{\text{nucleon}}$ in a carbon target were detected in coincidence with deexciting $\gamma$ rays. The widths of the longitudinal momentum distributions of the ${}^{22}\mathrm{O}$ fragments and the one-neutron removal cross sections were interpreted in the framework of a simple theoretical model which favors the assignment of $I^{\pi }=1/2^{+}$ to the ${}^{23}\mathrm{O}$ ground state.

Figure 1

Left: Inclusive longitudinal momentum distribution ($p_{\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}}$) for ${}^{22}\mathrm{O}$ fragments after one-neutron removal from ${}^{23}\mathrm{O}$. Right, top: Exclusive longitudinal momentum distribution for ${}^{22}\mathrm{O}$ in its ground state. Right, bottom: Longitudinal momentum distribution for ${}^{22}\mathrm{O}$ in any excited state.

Figure 2

Spectrum of $\gamma$ rays in coincidence with ${}^{22}\mathrm{O}$ fragments after one-neutron removal from ${}^{23}\mathrm{O}$ in a carbon target. The spectrum shown has been obtained from the measured $\gamma$-ray spectrum (see text). The experimental spectrum is compared with the result of a GEANT simulation adopting the level scheme shown above.

Figure 3

Ground-state exclusive momentum distribution for ${}^{22}\mathrm{O}$ fragments after one-neutron knockout reaction from ${}^{23}\mathrm{O}$ compared with calculations assuming $l=0$ and $l=2$ (see text).