An Isoratio Method and an Isoratio Scaling Phenomenon in Heavy-Ion Collisions

An isoratio method is proposed to study the chemical potential of neutrons (protons) from the yield ratio of isotopes (isotones) differing in neutron-excess (I = N-Z). The measured fragments in the 140 A MeV^40,48 Ca and ^58,64 Ni + ⁹ Be reactions, as well as those in the simulated ^58,64 Ni + ⁹Be reactions by using the antisymmetric molecular dynamics (AMD) model plus the secondary decay model gemini, have been adopted to perform the isoratio analysis. The results of the isoratio method verify that they are similar to that of the well known isoscaling method. The isoratio scaling phenomenon suggested by the isoratio method has also been found in the measured data and the fragments simulated by the AMD + gemini models.