Momentum distributions of {sup 9}Li fragments from the breakup of {sup 11}Li and the neutron halo

The inclusive parallel momentum distributions of {sup 9}Li fragments from the breakup of a secondary {sup 11}Li beam have been measured at 66 MeV/nucleon over a wide range of targets ({sup 9}Be to {sup 238}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 {sup 238}U where a distribution with a width of FWHM=38.1{plus_minus}1.9 MeV/{ital c} was observed. Together with a remeasurement of breakup on {sup 93}Nb (FWHM)=42.8{plus_minus}2.6 MeV/({ital 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 {sup 9}Li fragment parallel momentum distributions are relatively insensitive to the reaction and reflect the extended neutron distribution of the halo.