Isotopic yields and symmetry energy in nuclear multifragmentation reactions

Isotopic yields of light intermediate mass fragments (Z <= 8) were studied with data from the MSU experiments for central collisions of Sn-124 + Sn-124 and Sn-112 + Sn-112 at E/A = 50 MeV. Within the statistical multifragmentation model, microcanonical Markov-chain calculations were performed with the aim to reproduce experimental elemental and isotopic distributions. The effects of varying liquid-drop parameters of hot fragments formed inside the freeze-out volume on charge and isotopic distributions are demonstrated. It is seen that the isotopic distributions of these fragments are very sensitive to the variation of the symmetry energy of fragments. Comparing our results with the experimental data, it is seen that a significant reduction of the symmetry term coefficient leads to better reproduction of the isotopic distributions. Comparison with other statistical calculations has been made. This is in agreement with previous conclusions obtained from the interpretation of both central and peripheral heavy ion collisions.