Positron-Annihilation Momentum Profiles in Aluminum: Core Contribution and the Independent-Particle Model

Doppler Broadening of In-Flight Positron Annihilation Radiation due to Electron Momentum

“…For both the delocalized and trapped positrons, the dominant decay mode is by the emission of two g rays which are nearly collinear and have energies close to the electron rest mass energy of m 0 c 2 . Since a thermalized positron contributes a negligible amount of momentum to the annihilating pair, any deviations in the g-ray energies from m 0 c 2 511 keV can be directly correlated to the electron momentum [1,2]. Consequently, the width and shape of the 511 keV annihilation line yields information concerning the electrons with which the positrons annihilate.…”

“…Moreover, the annihilation with these outer electrons is further enhanced because of the strong charge polarization induced by the positron [1]. This enhancement makes describing the annihilation rate with low-momenta electrons a complicated task, but for sufficiently high momenta positron-electron correlations become less important [2,4]. Theories neglecting these correlations are generally called independent-particle models (IPM) because the electron wave functions are assumed not to respond to the presence of the positron.…”

“…Positron annihilation spectroscopy is a well-known technique by which the momentum spectra of electrons in a solid may be obtained [1][2][3][4]. After reaching thermal energies positrons diffuse through a solid, during which some positrons annihilate, while others become localized in open-volume defects and other trapping centers before annihilation [3].…”

Identifying vacancy complexes in compound semiconductors with positron annihilation spectroscopy: A case study of InN

“…and 0.995 MeV (0.53 a.u.) full width at half maximum (FWHM) at 0.511 MeV in the conventional and coincidence Doppler setup, 26,27 respectively. In the latter configuration, both annihilation photons are detected simultaneously and only counted if energy conservation is fulfilled (E tot = 1.022 MeV).…”

Spatially resolved deformation studies on carbon steel employing X‐rays and positron annihilation

“…Generally, DBAR measurements provide information about the momentum of the annihilating electron-positron pair. Trapped in a vacancy or a vacancy-like defect, the positron sees a different momentum distribution than when annihilating in the interstitial region (free positron state) [1][2][3]. Plastic deformation is always accompanied by the production of associated, non-equilibrium point defects like vacancies.…”