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Energy-dependent global Dirac optical model potentials are found by fitting proton elastic scattering data in the energy range 20--1040 MeV for ^12C, ^16O, ^40Ca, ^90Zr, and ^208Pb. Three different energy- and atomic-mass-number-dependent global Dirac optical potentials are also obtained. A number of characteristic features of the potentials are discussed. In addition, the mean free path, the effective mass m₄^*, the Dirac mass M^*, and the relativistic energy shift E^* are calculated.
Cooper et al. (Fri,) studied this question.