Nanocomposites and nanomaterials

Kinetic of positron-electron annihilation in the frequency domain in water absorbed MgO-Al2O3 ceramics 
O. Ye. Fl’unt1, H. Klym2, A. Ingram3
1 Department of Electronics and Computer Technology, Ivan Franko National University of Lviv, Dragomanov Str., 50, Lviv-79005, Ukraine. 
2 Lviv Polytechnic National University, Bandery Str., 12, Lviv-79013, Ukraine.
E-mail: halyna.i.klym@lpnu.ua; klymha@yahoo.com 
3 Opole University of Technology, Ozimska Str., 75, Opole- 45370, Poland.

Positron-electron annihilation (PEA) process kinetic can be represent in frequency domain in the form of spectra of in-phase and quadrature (shifted on π/2 on phase) components on frequency of positron flux intensity modulation [1]. Kinetic analysis in the frequency domain has some advantages in comparison with analysis of kinetic processes in the time domain. In the frequency domain it is possible to analyze simultaneously the spectra of as real, so imaginary part of flux intensity modulated PEA response, that strengths the validity of obtained form of kinetic processes. Now intensity positron flux modulated spectra in solids can’t be measured directly, because of absence of positron flux chopper in Gigahertz frequency range. In this work complex frequency spectra of PEA kinetic in the frequency domain in water-adsorbed MgO-Al2O3 ceramic have been obtained by numerical calculation of integral Fourier transforms of PEA kinetic in the time domain. 
Effect of water absorption on kinetic of EPA in the MgO-Al2O3 ceramics sintered at different temperatures (1100, 1200 and 1400 oC) has been analyzed in the frequency domain. The numerical calculations of the spectra were carried out using cubic-spline interpolation of the pulse characteristics of MgO-Al2O3 ceramics in time domain with following analytical calculations of integrals. 
Two Debye-type short time kinetic components have been revealed on modulated PEA spectra of real and imaginary parts of water-absorbed MgO-Al2O3 ceramics. This confirms the appearing of additional relaxation term caused by water absorption. 
1. Fl’unt O., Klym H., Ingram A. Frequency domain kinetic of positron–electron annihilation in the MgO–Al2O3 spinel-type ceramics // Applied Nanoscience. – 2018. – P. 1-6. 
https://doi.org/10.1007/s13204-018-0702-3