Secondary decay effects of the isospin fractionation in the projectile fragmentation at GeV/nucleon

The isospin fractionations in ^124 Sn, ^107 Sn + ^120 Sn at 600 MeV/nucleon, and ^136 Xe, ^124 Xe + ^208 Pb at 1000 MeV/nucleon are investigated by the isospin-dependent quantum molecular dynamics model coupled with the statistical code GEMINI. The yield ratio as a function of the binding energy difference for light mirror nuclei ^3 H/ ^3 He, ^7 Li/ ^7 Be, ^11 B/ ^11 C, and ^15 N/ ^15 O is applied to estimate the ratio between neutrons and protons in the gas of the fragmenting system. By comparing the estimated values resulting from the simulations with and without the GEMINI code, it was found that the secondary decay distorts the signal of the isospin fractionation. To minimize the secondary decay effects, the yield ratio of the light mirror nuclei ^3 H/ ^3 He as well as its double ratio between two systems with different isospin asymmetries of the projectiles is recommended as robust isospin observables.