Calculation of Gamma Spectra for Positron Annihilation on Molecules

Abstract:

Article Preview

Calculations of gamma spectra for positron annihilation for a selection of molecules, including methane and its fluoro-substitutes, ethane, propane, butane and benzene are presented. The contribution to the -spectra from individual molecular orbitals is obtained from electron momentum distributions calculated using the density functional theory (DFT) based B3LYP/TZVP model. For positrons thermalised to room temperature, the calculation, in its simplest form, effectively treats the positron as a plane wave and gives positron annihilation  spectra linewidths that are broader (30–40%) than experiment, although the main chemical trends are reproduced. The main physical reason for this is the neglect of positron repulsion from the nuclei. We show that this effect can be incorporated through momentum-dependent correction factors, determined from positron-atom calculations, e.g., many-body perturbation theory. Inclusion of these factors in the calculation gives linewidths that are in improved agreement with experiment.

Info:

Periodical:

Edited by:

Radosław Zaleski

Pages:

21-24

DOI:

10.4028/www.scientific.net/MSF.666.21

Citation:

D.G. Green et al., "Calculation of Gamma Spectra for Positron Annihilation on Molecules", Materials Science Forum, Vol. 666, pp. 21-24, 2011

Online since:

December 2010

Export:

Price:

$35.00

In order to see related information, you need to Login.

In order to see related information, you need to Login.