Fragment emission from the mass-symmetric reactions Fe-58,Ni-58 +Fe-58,Ni-58 at E-beam=30 MeV/nucleon
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The mass-symmetric reactions [Formula Presented] were studied at a beam energy of [Formula Presented] in order to investigate the isospin dependence of fragment emission. Ratios of inclusive yields of isotopic fragments from hydrogen through nitrogen were extracted as a function of laboratory angle. A moving source analysis of the data indicates that at laboratory angles around [Formula Presented] the yield of intermediate mass fragments (IMFs) beyond [Formula Presented] is predominantly from a midrapidity source. The angular dependence of the relative yields of isotopes beyond [Formula Presented] indicates that the IMFs at more central angles originate from a source which is more neutron deficient than the source responsible for fragments emitted at forward angles. The charge distributions and kinetic energy spectra of the IMFs at various laboratory angles were well reproduced by calculations employing a quantum molecular-dynamics code followed by a statistical multifragmentation model for generating fragments. The calculations indicate that the measured IMFs originate mainly from a single source. The isotopic composition of the emitted fragments is, however, not reproduced by the same calculation. The measured isotopic and isobaric ratios indicate an emitting source that is more neutron rich in comparison to the source predicted by model calculations. 1998 The American Physical Society.