One-neutron removal reactions on light neutron-rich nuclei

A study of high-energy (43-68 MeV/nucleon) one-neutron removal reactions on a range of neutron-rich psd-shell nuclei (Z=5-9, 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 B-15,C-17,N19-21,O-21,O-23,F23-25. In addition to the large spectroscopic amplitudes for the nu2s(1/2) intruder configuration in the N=9 isotones, B-14 and C-15, significant nu2s(1/2)(2) admixtures appear to occur in the ground state of the neighboring N=10 nuclei B-15 and C-16. Similarly, crossing the N=14 subshell, the occupation of the nu2s(1/2) orbital is observed for O-23, F-24,F-25. Recent claims of a modified shell structure for O-23 are investigated and the original suggestion of a ground state J(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.