Angular Distribution of Positron Annihilation Radiation in Aluminum–Experiment

Angular distributions of two photons resulted from annihilation of positrons in Al were measured along three principal crystallographic directions. The observed distribution curves were compared with the results of the APW calculation by Kubo et al. The fine structures and the anisotropies of the experimental curves verified theoretical predictions and were interpreted in terms of the shapes of the Fermi surfaces. A slight discrepancy that the theoretical curves were a little narrower than the experimental ones in the main part of the curves was found. This discrepancy is ascribed to the effect of the positron-electron interaction. By introducing enhancement factors much better agreement has been attained.