As a contribution to the dynamic irradiation-elution method using ion-exchanger, in which, during the progress of irradiation, the product resulting from irradiation is immediately separated upon recoil from the complex-ion target adsorbed on an ion-exchanger, the concentration of the separable recoiling species remaining in the bead and the film of the ion-exchanger in stationary condition was derived theoretically as a function of bead radius, with parameters to account for various others factors such as initial yield, film thickness, recombination rate constant of the recoiling species, and their diffusion coefficients. The equation derived for the separable yield was applied successfully to the analysis of experimental results obtained on trioxalatochromium ion adsorbed on an ion-exchange resin.