Projectile fragmentation of ¹²⁹Xe at E_lab=790A MeV

We have measured production yields and longitudinal momentum distributions of projectilelike fragments in the reaction ¹²⁹Xe+²⁷Al at an energy of E_lab=790A MeV. Production cross sections higher than expected from systematics were observed for nuclei in the neutron-deficient tails of the isotopic distributions. A comparison with previously measured data from the fragmentation of ¹³⁶Xe ions shows that the production yields strongly depend on the neutron excess of the projectile with respect to the line of β stability. The momentum distributions exhibit a dependence on the fragment neutron-to-proton ratio in isobaric chains, which was not expected from systematics so far. This can be interpreted by a higher excitation of the projectile during the formation of neutron-deficient fragments.