DEPTH-PROFILING STUDIES OF ION-IMPLANTED CESIUM AND RUBIDIUM IN SIMFUEL AND URANIUM-DIOXIDE

The distributions of rubidium and cesium ion-implanted at 40 keV in UO 2 and a UO2-based SlMFUEL have been depth-profiled by secondary ion ma ss spectrometry and X-ray photoelectron spectroscopy in conjunction wi th argon-ion sputtering. A pronounced spike in the near-surface concen tration of rubidium or cesium was found superimposed on the depleted r esidual projected-range profile. This redistribution provides a convin cing explanation for the anomalous low-temperature release of ion-impl anted radiotracers observed in many previous thermal diffusion studies . No evidence was obtained of a similar effect for ion-implanted krypt on. Calibration of the argon-ion sputtering rate for UO2 was achieved by comparison of measured and calculated implanted-ion distributions o n the least distorted back side of the profile. The results also offer new insight into radiation-enhanced fission-product migration and seg regation in oxide nuclear fuels.