International Workshop on Physics with Positrons at Jefferson Lab (JPos17)

Developing new routine for processing coincidence Doppler energy spectra

Not scheduled

15m

Room F113 (CEBAF Center)

Poster

Speaker

Petr Stepanov (1Center for Photochemical Sciences, Bowling Green State University, OH, USA)

Description

Coincidence Doppler broadening (CDB) spectroscopy is a powerful technique to characterize defects and study electron-positron states in a wide range of materials. 
A new method for processing a two-dimensional Doppler spectrum into a single-dimensional one was developed. The new routine performs two-dimensional background fitting of the CDB spectra and its subtraction from raw experimental data. This procedure provides more clean CDB spectrum which contains registered pairs of annihilation photons produced in the same two-gamma e+e- annihilation event. This results in a more adequate observation of defects and electron momentum distributions.

 ![Fig. 1. Background fit of the two-dimensional CDB spectrum of aluminum. E1 and E2 are energies of gamma-quanta registered by two HPGe-detectors.][1] Fig. 1a depicts the background contribution into the CDB spectrum. It accounts on the coincidence of one of the photons with the Compton-scattered photon from Na22 beta decay. Additionally, we subtract the contribution of the coincidence with the photons produced in three-gamma annihilation process. The background fit function is convoluted with respect to the both detectors’ resolution functions. To analyze a single-dimensional CDB spectrum we decompose it into a sum of parabola (in metals) and Gaussian functions (other trial functions, which follow from the simplest theoretical models for the electron momentum distributions were used as well). It allows us to estimate the Fermi energies and the energies of core electrons involved into the positron annihilation process and judge about the presence of the vacancy type defects in solids. [1]: http://physics.bgsu.edu/selimlab/wp-content/uploads/2017/08/pic.png