Isotopic scaling of heavy projectile residues from the collisions of 25 MeV/nucleon 86Kr with 124Sn, 112Sn and 64Ni, 58Ni
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The scaling of the yields of heavy projectile residues from the reactions of 25 MeV/nucleon 86Kr projectiles with 124Sn, 112Sn and 64Ni, 58Ni targets is studied. Isotopically resolved yield distributions of projectile fragments in the range Z= 10-36 from these reaction pairs were measured with the MARS recoil separator in the angular range 2.7-5.4. For these deep inelastic collisions, the velocities of the residues, monotonically decreasing with Z down to Z 26-28, are employed to characterize the excitation energy. The ratios R 21(N,Z) of the yields of a given fragment (N,Z) 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 =0.43 and = -0.50 for the Kr+Sn system and = 0.27 and =- 0.34 for the Kr+Ni system. For the Kr+Sn system, for which the experimental angular acceptance range lies inside the grazing angle, isoscaling was found to occur for Z 26 and N34. For heavier fragments from Kr+ Sn, the parameters vary monotonically, decreasing with Z and 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 N/Z 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.
