Multiple emission of intermediate-mass fragments (IMFs) is one of the salient reaction modes in heavy-ion collisions in the Fermi-energy domain (E/Aapproxapprox to 100 MeV).~(1) It has been established that for heavy systems, and at the lower boundary of the Fermi energy regime (E/A approxapprox30 MeV), sequential thermal IMF emission from either the projectile-like freagment (PLF) or the target-like fragment between PLF and TLF, both in peripheral(2,3,4) and in central~(6) collisions. It has also been shown that in peripheral collisions the "neck zone' is transiently formed from the neutron-rich projectile and target surface matter.~(3,7) These findings are consistent with a dynamical IMF production scenario, such as that of microscopic molecular dynamics models.~(8,9,10) Since protons and alpha-particles are emitted mostly sequentially from PLF and TLF,(3,5) while in the same events, IMFs are emitted mostly from a midrapidity "neck-like" source, a single fused system can be ruled out as a possible source of all particles and fragments, for nearly the entire observed cross section.
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