Helium implanted ZrHf as studied by time differential perturbed angular correlation and positron lifetime measurements

Abstract

Time differential perturbed angular correlation (TDPAC) at the 482 keV state of 181Ta and positron lifetime measurements were performed on homogeneously helium implanted ZrHf samples. TDPAC on the as-implanted sample shows the association of 0.12±0.02 fraction of probe nuclei with stacking faults experiencing a local fcc environment. The dissociation of this defect complex from probe nuclei is observed following the annealing treatment at 423 K. TDPAC measurements lead to the conclusion that Hf impurities do not bind He-vacancy complexes or helium bubbles in ZrHf. A recovery stage associated with helium migration is identified from the variation of the relative width of the Lorentzian distribution of the quadrupole frequency in TDPAC measurements. This correlates well with the variation of the helium associated positron lifetime component. The nucleation and growth stages of He bubbles in the sample have been identified by positron lifetime measurements as a function of the annealing temperature on the irradiated sample. Based on the analysis of positron lifetime measurements, helium bubble parameters such as bubble radius and bubble concentration have been extracted in the growth stage, leading to a quantitative understanding of the bubble growth in ZrHf.