Isotopic scaling of heavy projectile residues from the collisions of 25 MeV/nucleon Kr-86 with Sn-124, Sn-112 and Ni-64, Ni-58
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abstract
The scaling of the yields of heavy projectile residues from the reactions of [Formula Presented] projectiles with [Formula Presented] and [Formula Presented] targets is studied. Isotopically resolved yield distributions of projectile fragments in the range [Formula Presented] from these reaction pairs were measured with the MARS recoil separator in the angular range [Formula Presented] For these deep inelastic collisions, the velocities of the residues, monotonically decreasing with Z down to [Formula Presented] are employed to characterize the excitation energy. The ratios [Formula Presented] of the yields of a given fragment [Formula Presented] from each pair of systems are found to exhibit isotopic scaling (isoscaling), namely, an exponential dependence on the fragment atomic number Z and neutron number N. The isoscaling is found to occur in the residue Z range corresponding to the maximum observed excitation energies. The corresponding isoscaling parameters are [Formula Presented] and [Formula Presented] for the [Formula Presented] system and [Formula Presented] and [Formula Presented] for the [Formula Presented] system. For the [Formula Presented] system, for which the experimental angular acceptance range lies inside the grazing angle, isoscaling was found to occur for [Formula Presented] and [Formula Presented] For heavier fragments from [Formula Presented] the parameters vary monotonically, [Formula Presented] decreasing with Z and [Formula Presented] increasing with N. This variation is found to be related to the evolution towards isospin equilibration and, as such, it can serve as a tracer of the [Formula Presented] equilibration process. The present heavy-residue data extend the observation of isotopic scaling from the intermediate mass fragment region to the heavy-residue region. Interestingly, such high-resolution mass spectrometric data can provide important information on the role of isospin and isospin equilibration in peripheral and midperipheral collisions, complementary to that accessible from modern large-acceptance multidetector devices. 2003 The American Physical Society.
