Radiatively Generated Parton Distributions of Polarized Hadrons and Photons

A next-to-leading order QCD analysis of spin asymmetries and structure functions in polarized deep inelastic lepton nucleon scattering is presented within the framework of the radiative parton model. The $Q^2$-dependence of the spin asymmetry $A_1^{p}(x,Q^2)$ is shown to be non-negligible for $x$-values relevant for the analysis of the present data. In the second part of the paper we present LO results for radiatively generated spin-dependent parton distributions of the photon and for its structure function $g_1^{\gamma}$.