The scale dependence of the ratios of parton distributions in a proton of a nucleus A and in the free proton, (R_i^A(x,Q^2)=f_{i/A}(x,Q^2)/f_i(x,Q^2)), is studied within the framework of the lowest order leading-twist DGLAP evolution. By evolving the initial nuclear distributions obtained with the GRV-LO and CTEQ4L sets at a scale (Q_0^2), we show that the ratios (R_i^A(x,Q^2)) are only moderately sensitive to the choice of a specific modern set of free parton distributions. We propose that to a good first approximation, this parton distribution set-dependence of the nuclear ratios (R_i^A(x,Q^2)) can be neglected in practical applications. With this result, we offer a numerical parametrization of (R_i^A(x,Q^2)) for all parton flavours i in any (A>2), and at any (10^{-6}le x le 1) and any (2.25 { m GeV}^2le Q^2le 10^4,{ m GeV}^2) for computing cross sections of hard processes in nuclear collisions.
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