Abstract
Hydrogen--vacancy interaction in tungsten was investigated by means of the perturbed angular correlation technique, using the isotope exp 111 In as a probe. Hydrogen trapping at an exp 111 In-vacancy cluster manifests itself as a change of the local electric field gradient, which gives rise to an observable shift of the quadrupole frequency. The measurements show that a vacancy in W can trap one or two H atoms at room temperature. The detrapping energies of the first and second H atom ar 1.55(2) and 1.38(2) eV, respectively, while the detrapping energy of the next H atom is < 1.1 eV. Substitutional exp 111 In atoms do not trap H at room temperature. At least two more H decorated defects were observed. Although their structures are not quite clear, they probably form from larger vacancy clusters and may contain a large amount of H. The dissociation energy of these bubble-like defects is 1.30(2) eV.