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 UO2 and a UO2-based SlMFUEL have been depth-profiled by secondary ion mass spectrometry and X-ray photoelectron spectroscopy in conjunction with argon-ion sputtering. A pronounced spike in the near-surface concentration of rubidium or cesium was found superimposed on the depleted residual projected-range profile. This redistribution provides a convincing explanation for the anomalous low-temperature release of ion-implanted radiotracers observed in many previous thermal diffusion studies. No evidence was obtained of a similar effect for ion-implanted krypton. Calibration of the argon-ion sputtering rate for UO2 was achieved by comparison of measured and calculated implanted-ion distributions on the least distorted back side of the profile. The results also offer new insight into radiation-enhanced fission-product migration and segregation in oxide nuclear fuels.