Evidence of “slow” relaxation of isospin degree of freedom

Isotope ratios, as a function of kinetic energy in units of MeV/u of outgoing particles, are analyzed at 20° in the reaction of 40Ar+112,124Sn and 5° in 36Ar+112,124Sn at incident energy of 35 MeV/u. Relative yield ratios to stable isotopes increase with kinetic energy for the isotopes with low N/Z ratio but decrease for those with high N/Z ratio. This different behavior shows evidence of isospin non-equilibrium in dissipative projectile emission processes. It is demonstrated that the time of isospin relaxation is shorter as or comparable with that of energy relaxation in these reactions. Double isotope-ratio temperature parameters, extracted in the 36Ar induced reaction from projectile-like fragments, also support the non-equilibrium of isospin or/and temperature degrees of freedom.