Dissipative Collisions and Multifragmentation in the Fermi Energy Domain

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Multiple emission of intermediate-mass fragments (IMFs) is one of the salient reaction modes in heavy-ion collisions in the Fermi-energy domain (E/A ≈ 10 to 100 MeV).[1] It has been established that for heavy systems, and at the lower boundary of the Fermi energy regime (E/A ≈ 30 MeV), sequential thermal IMF emission from either the projectile-like fragment (PLF) or the target-like fragment (TLF) is rather weak.[3,5] IMFs are rather emitted from the “neck zone” formed 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 α-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.