Physico-chemical changes accompanying the irradiation of ammonium molybdophosphate (AMP) with electrons up to a dose of 200 MGy have been studied by X-ray di †raction, SEM, EDX, thermal analyses, EPR and NMR measurements. The ion exchange characteristics of the control and irradiated AMP with respect to Cs`have been studied using simulated acidic nuclear waste solutions in a column. Apparent equilibrium constants for the Cs`ÈH`exchange have been calculated from breakthrough curves. Structural breakdown occurred on irradiating AMP to a dose of 100È200 MGy and was partially converted to and MoO 3 ammonium molybdate. Although the useful exchange capacities of the irradiated AMP were reduced, the apparent ion exchange selectivity for Cs`(with respect to H`) improved as compared to the control AMP.