Xe-implanted zirconium oxycarbide studied by variable energy positron beam

Variable energy positron beam study of Xe-implanted uranium oxide

“…The same estimation cannot be transferred directly for Ps annihilation in Xe bubbles. In agreement with the conclusions in references [31,32], in a study of Xe implantation in zirconium carbide we have found that Xe is efficient for oPs into p-Ps conversion [5]. The o-Ps into p-Ps conversion significantly increases the resulting S Ps , thus, the estimation S Ps = 0.586 (or S Ps =S average bulk = 1.174) can be used only as the lower limit in the case of Ps in Xe bubbles.…”

“…As can be seen in Table 2, the S Ã d parameter for I 0 and I, for which the Xe concentration defers by factor of 10, is almost the same $0.53 which confirm the last expectation. As seen in Table 2, the defects distribution at higher fluence of 10 16 Xe cm À2 (sample I) is situated closer to the surface at d = 41 nm and this effect of Xe fluence is similar to what is observed in Xe-implanted zirconium carbide [5]. This fact together with the rather narrow widths of the defects distributions for I 0 and I is in discrepancy with the dpa profile calculated by SRIM.…”

“…In both modes, operational and spent fuel storage the understanding of the retention of these fission gases is of great importance. These noble fission gases have a low solubility in UO 2 and do not interact with it or with any other fission product, and, as a result, Xe segregates and forms bubbles [1,2], which have been observed as well in other materials [3][4][5][6]. The nucleation and diffusion of Xe bubbles in UO 2 have been studied by different experimental methods such as Electron Probe Micro Analysis (EPMA) [7], Secondary Ions Mass Spectroscopy (SIMS) [8], X-ray absorption spectroscopy (XAS) [9], and Transmission Electron Microscopy (TEM) [10][11][12].…”

“…to work in direction of annealing open volume defects. The model calculation of electron momentum distribution of vacancy clusters in ZrC decorated with Xe leaded to decrease of S parameter for e + annihilation [5]. That is why the high S Ã d parameter (0.55-0.57, see Table 2) implies a contribution from Ps annihilation either in voids or in Xe bubbles.…”

“…This depth position is much less than the Xe projected range R Xe = 148 -nm but it is in agreement with the peak position of dpa R d = 72 nm. For a material with covalent bonds (ZrC) we have shown that positrons sensitivity is negligible to Xe interstitials caused by Xe-implantation [5]. The ionic bonds in UO 2 determine defects (interstitials, Frenkel pairs, Schotky) most of them charged and positrons due to their positive charge will be sensitive to negatively charged defects, i.e.…”