Many-body theory of gamma spectra from positron–atom annihilation

Abstract

A many-body theory approach to the calculation of gamma spectra of positron annihilation on many-electron atoms is developed. We evaluate the first-order correlation correction to the annihilation vertex and perform numerical calculations for the noble gas atoms. Extrapolation with respect to the maximal orbital momentum of the intermediate electron and positron states is used to achieve convergence. The inclusion of correlation corrections improves agreement with experimental gamma spectra.

Calculations of gamma-ray spectral profiles of linear alkanes in the positron annihilation process

“…[12] As a result, molecules are very different from atoms where the electrons in the HOMO exhibit the largest probability to annihilate a positron. [6] determined from the docking. Table 2 summaries the information of these alkanes which the gamma-ray spectra are calculated.…”

“…The spherically averaged gamma-ray spectra for each type of electrons are then calculated by using general equations, [6,7] (10)…”

“…Certainly, the Doppler shift (∆ε, i.e, the full width at half maximum (FWHM)) has been recognised as the most important parameter to quantify the spectra of molecules [1][2][3][4][5][6][7] and is closely correlated to electron momentum distribution of the molecule. [7] However, the full width at half maximum (FWHM, ∆ε) parameter can be a necessary but not a sufficient condition to ensure the goodness of the calculated momentum profiles.…”

Ab initio QED Treatment of the Two-Photon Annihilation of Positrons with Bound Electrons

“…These processes can be well described in the framework of the nonrelativistic Lee's [24] approximation. On the basis of this approximation the theoretical approach which shows a remarkable agreement with related experimental studies was developed [25][26][27][28].…”

“…On the basis of this approximation, the theoretical approach which shows a remarkable agreement with related experimental studies was developed [25][26][27][28]. For ultra-fast positrons, in contrast, the impulse approximation can be applied, in which all particles are assumed to be free and where the active electron is represented by a stationary wave packet of superimposed plane-wave states.…”