Momentum distributions of ⁹Li fragments following the breakup of ¹¹Li

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 ⁹Li nuclei produced in the breakup of ¹¹Li. Measurements were made for 66-MeV/nucleon ¹¹Li projectiles on ⁹Be, ⁹³Nb, and ¹⁸¹Ta targets. Distributions with Gaussian width of σ_∥≊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 ¹¹Li.