Momentum distributions ofLi9fragments from the breakup ofLi11and the neutron halo

Abstract

The inclusive parallel momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ fragments from the breakup of a secondary ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ beam have been measured at 66 MeV/nucleon over a wide range of targets ${(}^9$Be to ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$). The measurements were performed using a zero-degree fragment separator as an energy-loss spectrometer operating in a dispersion matched mode. Earlier measurements have been extended here to the case of breakup by ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ where a distribution with a width of FWHM=38.1±1.9 MeV/c was observed. Together with a remeasurement of breakup on ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ (FWHM)=42.8±2.6 MeV/c) a weak dependence of distribution width on target nucleus was observed. A discussion of the nature of the momentum distributions and relationship to the structure of the halo is presented in the light of recent calculations. It is concluded that the ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ fragment parallel momentum distributions are relatively insensitive to the reaction and reflect the extended neutron distribution of the halo.