4 time 10 fm 4.5  x 10  s -22 6.0  x 10  s -22 7.5  x 10  s -22 Mg + O 24 24 Mg + Pb 24 208 time 10 fm 4.5  x 10  s 7.5  x 10  s 10.5  x 10  s (a) (b) FIG. 4: Real-time dynamics of charge distribution for $^{24}$Mg + $^{24}$O and $^{24}$Mg + $^{208}$Pb (SLy4d) are shown for E cm /A = 4.5 MeV and 2.0 MeV with the impact parameters 5.0 fm and 7.5 fm, respectively. For both cases, $^{24}$Mg is incoming from the left, and the states are evolving into fusion. The description manner is the same as Fig. 3, where parts with the proton to neutron density ratio larger than 1.00 (0.75) and 0.80 (0.70) are colored in red and yellow in case of $^{24}$Mg + $^{24}$O ($^{24}$Mg + $^{208}$Pb), respectively. collisions between light nuclei. Similar results are ob- tained in [2–8]. Next, we move on to collisions involving a heavier nucleus; e.g. $^{24}$Mg + $^{208}$Pb, as shown in Fig. 4 (b). Charge-equilibration dynamics is not similar to the motion of the iv-GDR in this case, because no significant oscillations of the localized charge appear. Instead a radi- ally layered structure of the composite nucleus is formed (7.5 × 10 − 22 sec), in which a relatively neutron-rich core appears in the center, a proton-rich layer surrounds it, and a neutron-rich skin is in the surface. This seems to be due to the Coulomb repulsion, hence the radial distri- bution of charge is formed. Here one can find analogous situation of isovector monopole excitation. It means that the radial flow plays a prominent role in such low energy collisions. Similar layered structures are obtained in the TDHF calculations (with both Skyrme parameter-sets) listed in Table I except for $^{24}$Mg + $^{24}$O. Consequently, charge equilibration, which is dependent on the mass, has been clarified to be related not only with the isovector gi- ant dipole excitations, but also with the isovector giant monopole excitations. Finally, let us comment on the diffusion-type mech- anism towards charge equilibrium. The mechanism of charge equilibration discussed in this Letter is valid at lower energies (lower than the upper energy-limit). At much higher energies, collisions between nucleons and the diffusion contribute mostly to charge equilibration (for example, see [17, 18]). As the diffusion is a slow pro- cess, it is unlikely to attain the charge equilibrium within the initial stage. Energy-dependent equilibration mecha- nisms of a similar kind have been reported in condensed matter physics (see [19–21]), where the equilibration is fast for lower energies (temperatures), and quite slow for higher energies. Such a similarity between completely different physical systems is interesting. In this Letter the mechanism of charge equilibration, in which nucleons with the Fermi velocity play a primary role, has been presented, and its validity is examined by comparison to virtually all existing relevant experimental data. This concept has been further analyzed in terms of a three-dimensional time-dependent density function for- malism. The upper energy-limit of charge equilibration has a crucial impact on the nuclear synthesis of exotic nu- clei. Properties presented in this Letter will give a sound motivation for the production of further exotic isotopes by the latest and the future RI-beam facilities. This work was supported in part by EMMI project of the Helmholtz Alliance, by JSPS Core-to-Core pro- gram EFES and by grant-in-aid for Scientific Research (A) 20244022. Y.I. thanks for the JSPS fellowship, and express his gratitude to Dr. C. Simenel. T.O. thanks Prof. P. Bonche for long-term valuable collaboration. [1] H. Freiesleben and J.V. Kratz, Phys. Rep. 106 (1984) 1. [2] M. Berlanger, A. Gobbi, F. Haneppe, U Lynen, C. Ngˆ o and A. Olmi, Z. Phys. A 291 (1979) 133. [3] E.S. Hernandez, W.D. Myers, J. Randrup and B. Re- maud, Nucl. Phys. A 361 (1981) 483. [4] P. Bonche and N. Ngˆ o, Phys. Lett. B 105 (1981) 17. [5] E. Suraud, M. Pi, and P. Schuck, Nucl. Phys. A 492 (1989) 294. [6] V. Baran, D.M. Brink, M. Colonna, and M. Di Toro, Phys. Rev. Lett. 87 (2007) 182501. [7] C. Simenel, Ph. Chomaz, and G. de France, Phys. Rev. Lett. (2001) 2971. [8] C. Simenel, Ph. Chomaz, and G. de France, Phys. Rev. C 76 (2007) 024609. [9] W.D. Myers and W.J. Swiatecki, Ann. Phys. 55 (1969) 395. [10] W.D. Myers, Phys. Lett. 30B (1969) 451. [11] B. Gatty, D. Guerreau, M. Lefort, X. Tarrago and J. Galin, Nucl. Phys. A 253 (1975) 511. [12] H. Breuer et. al. , Phys. Rev. Lett. 43 (1979) 191. [13] P. M. Milazzo et. al. , Phys. Rev. C66 (2002) 021601. [14] W.P. Tan et. al. , Phys. Rev. C64 (2001) 051901. [15] M. Mocko et. al. , Phys. Rev. C76 (2007) 014609. [16] M.B. Tsang et. al. , Private communication. [17] L. Shi and P. Danielewicz, Phys. Rev. C 68 (2003) 064604. [18] M.B. Tsang et. al. , Phys. Rev. Lett. 102 (2009) 122701. [19] L.D. Landau and Zh. Eksperim, Soviet Phys. - JETP 5 (1957) 101. [20] W.R. Abel, A.C. Anderson, and J.C. Wheatley, Phys. Rev. Lett. 17 2 (1966) 74. [21] A.J. Leggett, Rev. Mod. Phys. 47 No.2 (1975) 331.