Angular Distribution of Positron Annihilation Radiation in Vanadium and Niobium–Experiment

Angular distributions of two photons resulted from annihilation of positrons in V and Nb were measured along three principal crystallographic directions and conspicuous structures and anisotropies were found. The observed curves were compared with the results of the APW calculation by Wakoh et al. The agreement between the theory and the experiment in the fine structures and the anisotropies was remarkable, supporting the validity of one-electron approximation scheme. However, a slight common discrepancy that the theoretical curves are a little lower than the experimental ones in small momentum region was found, suggesting the limitation of applicability of the independent particle model. Observed differences between V and Nb curves were attributed to the differences in details of the band structures of these metals.