Abstract.The quantum probability ux of a particle integrated over time and a distant surface gives the probability for the particle crossing that surface at some time. The relation between these crossing probabilities and the usual formula for the scattering cross section is provided by the ux-acrosssurfaces theorem, which w as conjectured by Combes, Newton and Shtokhamer. 1 We p r o ve t h e u xacross-surfaces theorem for short range potentials and wave functions without energy cuto s. The proof is based on the free ux-across-surfaces theorem (Daumer et. al.), 2 and on smoothness properties of generalized eigenfunctions: It is shown that if the potential V (x) d e c a ys like jxj ; at in nity with > n 2 IN then the generalized eigenfunctions of the corresponding Hamiltonian ; 1 2 + V are n ; 2 times continuously di erentiable with respect to the momentum variable.