Isospin of intermediate mass fragments produced in peripheral, midperipheral, and central collisions from the Ni-58+C-12,Mg-24 reactions at 34.5A MeV- art. no. 051602

Isotopic yields of IMF's produced in the Ni-58+ C-12, Mg-24 reactions at 34 .5A MeV are investigated. Analysis of experimental data from the CRL-Laval 4 pi multidetector array focuses on events where at least 75% (60%) of the charge and momentum were detected for the Ni-58+ (1)2(C) (Ni-58+ Mg-24) sys tem. Averaged isospin ratios (N/Z) for IMF's with Z=3 and 4 are plotted as a function of emission angle and parallel velocity in the center-of-mass fr ame. Results from simulations with the statistical codes SMM and GEMINI, as suming an equilibrated source, are compared to the experimental ratios. The ratios seem to indicate the presence of a midrapidity necklike structure t hat would produce IMF's richer in neutrons than the two main emitters, even for very central collisions.