Isospin fractionation in nuclear fragmentation

Isotopic distributions for light particles and intermediate mass fragments have been measured for Sn-112+Sn-112, Sn-112+Sn-124, Sn-124+Sn-112 and Sn-124+Sn-124 collisions at E/A=50 MeV. Isotope, isotone and isobar yield ratio techniques are utilized to obtain an estimate of the relative abundance of free neutrons and protons at breakup. Consistent with the predictions of statistical models, which include two components in the liquid gas phase transition, neutrons and protons are not uniformly distributed at breakup. Instead, the neutron excess is amplified in the light charged particles.