Room-Temperature Ta-181(TiO2): An e-gamma TDPAC Study

In this work, we report on the hyperfine parameters of the foreign Ta-181 probe in the rutile structure of the single crystal TiO2 using the e-gamma and gamma-gamma time differential perturbed angular correlation (TDPAC) technique. We implanted Hf-181 ions into a sample of single crystal rutile TiO2 in the Bonn Isotope Separator. The implanted sample was then thermally annealed at a temperature of 873 K for 315 min in a vacuum. The Hf-181 radioisotopes decayed by beta(-) emission, followed by a cascade to the ground of gamma rays or conversion electrons into a stable state Ta-181. The Ta-181 probe substitutes the Ti lattice site with a unique nuclear quadrupole interaction, allowing for the precise measurement of the largest electric field gradient (V-zz) and asymmetry parameter (eta). The hyperfine parameters obtained from the e-gamma TDPAC spectroscopy agree with those of the gamma-gamma TDPAC spectroscopy at room temperature, apart from a calibration factor, both from our experiments and the literature. This suggests that the electronic recombination following the internal conversion of the L shell electron takes less time (ps) than the intermediate lifetime of the metastable Ta-181 state (ns).