Isospin of intermediate mass fragments produced in peripheral, midperipheral, and central collisions from the ⁵⁸Ni+¹²C, ²⁴Mg reactions at 34.5A MeV

Isotopic yields of IMF's produced in the ⁵⁸Ni+¹²C,²⁴Mg reactions at 34.5A MeV are investigated. Analysis of experimental data from the CRL-Laval 4 π multidetector array focuses on events where at least 75% (60%) of the charge and momentum were detected for the ⁵⁸Ni+¹²C (⁵⁸Ni+²⁴Mg) system. 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 frame. Results from simulations with the statistical codes SMM and GEMINI, assuming an equilibrated source, are compared to the experimental ratios. The ratios seem to indicate the presence of a midrapidity necklike structure that would produce IMF's richer in neutrons than the two main emitters, even for very central collisions.