1. An ion implantation system for irradiating a workpiece, comprising (a) charged particle accelerator means for producing a flux of energetic ions, (b) flux distributing means for directing the flux over said workpiece in accord with a preselected scanning pattern function to obtain a desired ion implantation treatment, (c) sensor means for deriving a flux magnitude signal proportional to the instantaneous magnitude of the flux incident on the workpiece wherein the instantaneous dose suffered by said workpiece is represented, (d) dose imaging means jointly cooperative with said sensor means and said flux distributing means for accumulating a record of the distribution of the differential cumulative magnitude of the flux incident on the workpiece as a function of coordinates on the surface of said workpiece, said record comprising a differential cumulative dose distribution function, (e) dose evaluation means operative upon the record of the differential cumulative dose distribution function to derive a corrected scanning pattern function for modifying said preselected scanning pattern function during said ion implantation treatment.