Time evolution of positron affinity trapping at embedded nanoparticles by age-momentum correlation

A positron annihilation age-momentum correlation (AMOC) technique using a digital oscilloscope with high time resolution enabled us to directly estimate positron trapping rate to nano- and subnanoparticles embedded in materials by observing the annihilation time evolution of the momentum distribution of affinity-trapped positron-electron pairs. As a representative case we successfully apply the present technique to (sub)nano Cu particles embedded in an Fe-Cu dilute alloy after thermal aging. This enhances the ability of the positron annihilation method as a quantitative tool to detect ultrafine embedded particles which are difficult to observe by other techniques. We also show that the AMOC measurements give chemical information on the embedded particles through the positron trapping kinetic behavior.