The elastic scattering of polarized protons from 16 nuclides in the f-p shell region was measured at a bombarding energy of 65 MeV. A conventional optical model analysis has been performed thoroughly and good fits have been achieved. The asymmetry term in the optical potential was deduced. We found that the volume integral of the asymmetry term depends on the mass number, in contrast with the A-independence claimed in previous works. The depth of the term is about zero when A = ̄40, increases gradually with the increasing A, and amounts to 20 MeV at A -= 60.
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