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-1 24+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 s tatistical models, which include two components in the liquid gas phase tra nsition, neutrons and protons are not uniformly distributed at breakup. Ins tead, the neutron excess is amplified in the light charged particles.