Lasers in metrology

Abstract

The angular correlation of positron-annihilation radiation from a glassy, a partially crystalline and a crystalline Pdo,,75Cuo,06Sio 165 alloy as well as a pure palladium sample was measured. The angular correlation curve for the glassy alloy varies slightly upon crystallization, indicating that the glassy alloy contains negligible vacancy-like defects. The localization of the positron in the glassy state may account for this small change in the angular distribution. The low momentum region of the alloy curves shows an appreciable deviation from that of the free electron model. The observed Fermi momentum of the alloy is larger than that of Pd which agrees qualitatively with the calculated Fermi momentum based on the assumption that the d band of Pd in the alloy is completely filled by valence electrons from Si. The low momentum region of the alloy curve is much higher than that of Pd. The explanation of this is discussed in terms of the increase of the valence electron concentration, the strong association locally between Pd and Si, and the relative positron affinity in the alloy.