Momentum distributions ofLi9fragments following the breakup ofLi11

A new method, use of a fragment separator as an energy-loss spectrometer, has been developed and used to make the first measurements of the parallel momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ nuclei produced in the breakup of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$. Measurements were made for 66-MeV/nucleon ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ projectiles on ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ targets. Distributions with Gaussian width of ${\mathrm{\sigma }}_{\mathrm{\parallel }}$≊19 MeV/c were observed for all targets—the first time such a narrow structure has been observed for medium and high mass targets. From the weak dependence of width on breakup target it appears that the paralell momentum distributions are relatively insensitive to the interaction governing the breakup and reflect an extended neutron distribution for ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$.