Isotopic scaling of heavy projectile residues from the collisions of $25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}{\hspace{0.5em}}^{86}\mathrm{Kr}$ with ${}^{124}\mathrm{Sn},$ ${}^{112}\mathrm{Sn}$ and ${}^{64}\mathrm{Ni},$ ${}^{58}\mathrm{Ni}$

The scaling of the yields of heavy projectile residues from the reactions of $25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}{\hspace{0.5em}}^{86}\mathrm{Kr}$ projectiles with ${}^{124}\mathrm{Sn},$ ${}^{112}\mathrm{Sn}$ and ${}^{64}\mathrm{Ni},$ ${}^{58}\mathrm{Ni}$ targets is studied. Isotopically resolved yield distributions of projectile fragments in the range $Z=10\mathrm{}–36$ 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 $Z\simeq 26–28,$ are employed to characterize the excitation energy. The ratios $R_{21}\mathrm{}(N,Z)\mathrm{}$ of the yields of a given fragment $\mathrm{}(N,Z)\mathrm{}$ 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 $\alpha =0.43\mathrm{}$ and $\beta =-0.50$ for the $\mathrm{Kr}+\mathrm{Sn}$ system and $\alpha =0.27\mathrm{}$ and $\beta =-0.34$ for the $\mathrm{Kr}+\mathrm{Ni}$ system. For the $\mathrm{Kr}+\mathrm{Sn}$ system, for which the experimental angular acceptance range lies inside the grazing angle, isoscaling was found to occur for $Z<~26$ and $N<~34.$ For heavier fragments from $\mathrm{Kr}+\mathrm{Sn},$ the parameters vary monotonically, $\alpha$ decreasing with Z and $\beta$ 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.