Neutron-skin effects in isobaric yield ratios for mirror nuclei in a statistical abrasion-ablation model

Background: The isobaric yield ratio for mirror nuclei [IYR(m)] in heavy-ion collisions, which is assumed to depend linearly on x = 2(Z - 1)/A(1/3) of a fragment, is applied to study some coefficients of the energy terms in the binding energy, as well as the difference between the chemical potentials of a neutron and proton. It is found that the IYR(m) has a systematic dependence on the reaction, which has been explained as the volume and/or the isospin effects in previous studies. However, neither the volume nor the isospin effects can fully interpret the data.Purpose: We suppose that the IYR(m) depends on the neutron-skin thickness (delta(np)) of the projectile, and check the idea of whether the neutron-skin thickness effects can fully explain the systematic dependence of the IYR(m).Methods: A modified statistical abrasion-ablation model is used to calculate the reactions induced by projectiles of three series: (1) the calcium isotopes from Ca-36 to Ca-56 as projectiles with different limitations on the impact parameters (b(max)) to show the volume effects according to b(max); (2) the A = 45 isobars as the projectiles having different isospins and delta(np); and (3) projectiles having similar delta(np) to show whether the IYR(m) depends on the volume or the isospin of the projectile.Results: The IYR(m) shows a distribution of a linear part in the small-x fragments, and a nonlinear part in the large-x fragments. The linear part of IYR(m) is fitted. (1) In the calcium isotopic reactions, the IYR(m) depends on the isospin or the volume of the projectile, but delta(np) greatly influences the nonlinear part of the IYR(m). The IYR(m) does not depend on the colliding source in reactions of small b(max) for the nonneutron-rich projectiles, and does not depend on the collision sources in reactions by the neutron-rich projectiles. (2) In reactions of the A = 45 isobars, though IYR(m) depends on the isospin of projectile, IYR(m) shows small dependence on isospin if delta(np) > 0. (3) In the reactions of projectiles having similar delta(np), the IYR(m) in the small mass fragments show no dependence on the volume and the isospin of the projectile when the mass of the projectile is relatively large. Specifically, the dependence of IYR(m) on the mass of the isospin of the projectile vanishes when delta(np) similar to 0.02 fm.Conclusions: The linear and nonlinear parts of the IYR(m) are governed by the core and the surface (skin) of the projectile, respectively. The neutron-skin effects can well explain the systematic dependence of the IYR(m).