Multicomponent positron–electron annihilation kinetics in the MgO–Al2O3 ceramics in the frequency domain

Abstract

Multicomponent positron–electron annihilation kinetics in initially dried (after natural water adsorption and before water treated process) and with following immersion into water MgO–Al2O3 ceramics sintered at different temperatures (1100 ÷ 1400 °C) has been calculated and analyzed in the frequency domain. The spectra of real (in-phase) $$\chi_{1} \left( \omega \right)$$ and imaginary (quadrature) $$\chi_{2} \left( \omega \right)$$ components of modulated positron–electron annihilation response have been obtained numerically from temporal kinetic characteristics using integral Fourier transform. To calculate Fourier transform combined with spline cubic interpolation for short time range (below 5.5 ns) and piecewise linear interpolation for highly noisy longer times range, domain kinetics have been used. A special method has been proposed to obtain clear frequency response of low-intensive long time components of PEA kinetics, which are almost invisible on spectra because of dominating high-frequency Debye-type component. Strong high-frequency dispersion apparently consists of two Debye-type components with close characteristic frequencies, that leads to widening of large maximum. Low-frequency decay component with characteristic time of about 70 ns shows stronger dependence on sintering temperature of the ceramics and is characterized by significant deviation from Debye form of relaxation. This indicates the formation of some changing with time structures around positrons localized on long time traps.