One-neutron removal reactions on light neutron-rich nuclei

Abstract

A study of high-energy $(43--68\phantom{\rule{0.3em}{0ex}}\text{MeV}∕\text{nucleon})$ one-neutron removal reactions on a range of neutron-rich $psd$-shell nuclei $(Z=5--9,\phantom{\rule{0.3em}{0ex}}A=12--25)$ has been undertaken. The inclusive longitudinal and transverse momentum distributions for the core fragments together with the cross sections have been measured for breakup on a carbon target. Momentum distributions for reactions on tantalum were also measured for a subset of nuclei. An extended version of the Glauber model incorporating second-order noneikonal corrections to the Jeukenne, Lejeune, and Mahaux parametrization of the optical potential has been used to describe the nuclear breakup, while the Coulomb dissociation is treated within first-order perturbation theory. The projectile structure has been taken into account via shell-model calculations employing the $psd$ interaction of Warburton and Brown. Both the longitudinal and transverse momentum distributions together with the integrated cross sections were well reproduced by these calculations and spin-parity assignments are thus proposed for $^{15}\mathrm{B},^{17}\mathrm{C},^{19--21}\mathrm{N},^{21,23}\mathrm{O},^{23--25}\mathrm{F}$. In addition to the large spectroscopic amplitudes for the $\ensuremath{\nu}2{s}_{1∕2}$ intruder configuration in the $N=9$ isotones, $^{14}\mathrm{B}$ and $^{15}\mathrm{C}$, significant $\ensuremath{\nu}2{s}_{1∕2}^{2}$ admixtures appear to occur in the ground state of the neighboring $N=10$ nuclei $^{15}\mathrm{B}$ and $^{16}\mathrm{C}$. Similarly, crossing the $N=14$ subshell, the occupation of the $\ensuremath{\nu}2{s}_{1∕2}$ orbital is observed for $^{23}\mathrm{O}$, $^{24,25}\mathrm{F}$. Recent claims of a modified shell structure for $^{23}\mathrm{O}$ are investigated and the original suggestion of a ground state ${J}^{\ensuremath{\pi}}=1∕{2}^{+}$ is confirmed. Analysis of the longitudinal and transverse momentum distributions reveals that both carry spectroscopic information, often of a complementary nature. The general utility of high-energy nucleon removal reactions as a spectroscopic tool is also examined.