Systematic reduction of the proton-removal cross section in neutron-rich medium-mass nuclei.

Single-neutron and single-proton removal cross sections have been measured for medium-mass neutron-rich nuclei around Z = 50 and energies around 1000 A MeV using the FRagment Separator (FRS) at GSI. The measured cross sections confirm the relative low values of the proton-removal cross sections, observed since a long time ago and not yet understood. Model calculations considering the knock-out process together with initial- and final-state interactions describe the measured neutron-removal cross sections. Proton-removal cross sections are, however, significantly over-predicted by the same calculations. The observed difference can be explained to a large extent by the knock-out of short-range correlated nucleons from dominant neutron-proton pairs in neutron-rich nuclei. [ABSTRACT FROM AUTHOR]