Hf impurity and defect interactions in helium-implanted NiHf

TDPAC measurements on the reference and untreated sample indicate a loss in anisotropy which is attributed mainly to the association of probe atoms wi th defects produced by (n, gamma) reactions with isotopes of Ni and experie ncing combined magnetic and quadrupole interactions of comparable strengths . Evolution of defect free and substitutional fraction of probe atoms exper iencing Larmor frequency characteristic of Ni matrix has been studied as a function of isochronal annealing temperature in helium free alpha -irradiat ed and homogeneously helium-implanted samples. No defect associated Larmor precession frequency and/or quadrupole frequency could be deduced in these uncorrelated damage studies. Comparison of recovery stages in alpha -irradi ated and helium-implanted samples indicates the binding of helium associate d defects by Hf impurities. Segregation of Hf atoms is observed in the heli um free alpha -irradiated sample for annealing treatment at 973 K, while no such effect is observed in the helium-implanted sample for isochronal anne aling treatments up to 1273 K. (C) 2001 Elsevier Science B.V. All rights re served.