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

Time differential perturbed angular correlation (TDPAC) at the 482 keV stat e of Ta-181 and positron lifetime measurements were performed on homogeneou sly helium implanted ZrHf samples. TDPAC on the as-implanted sample shows t he association of 0.12 +/- 0.02 fraction of probe nuclei with stacking faul ts experiencing a local fee environment. The dissociation of this defect co mplex from probe nuclei is observed following the annealing treatment at 42 3 K. TDPAC measurements lead to the conclusion that Hf impurities do not bi nd He-vacancy complexes or helium bubbles in ZrHf. A recovery stage associa ted with helium migration is identified from the variation of the relative width of the Lorentzian distribution of the quadrupole frequency in TDPAC m easurements. This correlates well with the variation of the helium associat ed positron lifetime component. The nucleation and growth stages of He bubb les 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 s uch as bubble radius and bubble concentration have been extracted in the gr owth stage, leading to a quantitative understanding of the bubble growth in ZrHf (C) 1999 Elsevier Science B.V. All rights reserved.