Effect of water adsorption on positron–electron annihilation kinetics in the MgO–Al 2 O 3 ceramics in the frequency domain

Positron–electron annihilation kinetics in the MgO–Al 2 O 3 ceramics sintered at different temperatures (1100, 1200 and 1400 °C) with the following water adsorbtion procedure has been calculated and analyzed in a frequency domain. The spectra of real (in-phase) χ_ 1( ω) and imaginary (quadrature) χ_2( ω) components of modulated positron–electron annihilation response have been obtained numerically from temporal kinetic characteristics using integral Fourier transform. The obtained complex spectra of positron-electron annihilation in MgO–Al 2 O 3 ceramics in the frequency domain obey a sum of two Debye law components denying a correlation between elementary positron annihilation processes. Strong increasing of amplitude of lower frequency Debye component caused by water adsorbtion on the frequency spectra has been observed. Characteristic frequencies of Debye-type components of water-immersed samples show weaker dependencies on sintering temperature than in just-sintered ones. It is shown that position of large maxima on the frequency dependencies of imaginary part corresponds to the fastest average relaxation lifetime representing the most intensive interaction process of positrons with small cavity traps in solids.