Isotopic composition of fragments in nuclear multifragmentation - art. no.041602

In this Rapid Communication we present results from the analysis of the iso topic yields of fragments emitted in two selected reactions: the decay of t he quasiprojectile in Au+Au peripheral collisions at 35 MeV/nucleon, and th e disassembly of the unique source formed in Xe+Cu central reactions at 30 MeV/nucleon. We find that the relative yields of neutron-rich isotopes incr ease with the excitation energy of the emitting sources. In the framework o f a statistical multifragmentation model which reproduces fairly well the e xperimental observables, such behavior can be explained with the increase o f the N/Z ratio of the hot primary fragments. This corresponds to the stati stical evolution of the fragmentation mechanism as a function of the excita tion energy, from the decay into few small fragments with a heavy residue t o complete multifragmentation.