Samples were exposed to X-rays in reflection geometry, which led to exposure of either the surface region alone or the surface plus bulk solution. The reflection geometry allowed for simultaneous exposure of the sample and measurement of the surface adsorption. Although reversible cycling of ion surface adsorption was observed only when the surface and bulk solutions were both exposed, because of the employed reflection geometry, the observed processes indicate that exposure of the bulk solution alone is likely to create reversible cycling of ion adsorption. In that case, cycling would require only x-ray exposure of the DTPA in the bulk solution. X-ray exposure would release Nd from DTPA which then binds to DHDP at the surface. When X-rays are turned off