ИСТИНА

The evolution of the neutron single-particle energies of isotones with N=50 approaching to the neutron drip-line (see fig.1) is calculated within the dispersive optical model (DOM) [1]. The calculated energies of 1g9/2 and 2d5/2 states are close to the neutron separation energy -Sn(N,Z) and -Sn(N+1,Z) respectively and the particle-hole gap between them substantially decreases with decreasing Z number. Near the neutron drip line, the 2d5/2 and 2s1/2 level sequence changes, and the 2s1/2 state with l = 0 becomes the first predominantly unoccupied state. The absence of the centrifugal barrier for this state facilitates the halo structure of 70Ca to be formed. The result is consistent with the predictions of the halo structure of the Ca isotopes near the neutron drip line by the relativistic continuum Hartree-Bogoliubov and non-relativistic Skyrme Hartree-Fock-Bogoliubov calculations [2, 3]. 1. C. Mahaux, R.Sartor // Adv. Nucl. Phys. 20, 1 (1991). 2. J. Meng, H. Toki, J. Y. Zeng et al., Phys. Rev. C 65, 041302 (2002). 3. J. Terasaki, S. Q. Zhang, S. G. Zhou et al., Phys. Rev. C 74, 054318 (2006).