Importance of starting time for defect analysis using positron annihilation lifetime measurements

Abstract

Conventional positron annihilation lifetime measurements have focused on determining the lifetime and relative intensity of each lifetime component deduced by multicomponent analysis or the 'mean' lifetime deduced by single-component analysis. So far, little attention has been paid towards the starting time (T₀) on the spectrum's time axis. When analysing lifetime spectra with multiple components using an exponential function with a single-component, there is a difference between the experimental data and the fitted spectrum. Compensating for this difference causes a shift in the T₀ value in the fitted spectrum. This study examines the shifts in T₀ (ΔT₀) in positron lifetime spectrum analyses of metal samples with defects. We conducted simulations of trapping models and experiments with shot-peened stainless steel, verifying that ΔT₀ changed depending on the defect concentration even when almost all positrons were trapped (full trap). Therefore, we propose ΔT₀ as a new parameter for evaluating positron annihilation lifetime measurements.