The affinity-induced positron state was detected in ‘defect-free’ intermetallic particles using angular correlation of annihilation radiation. It was found that approximately 98% of the positrons annihilate within nanosized and subnanosized intermetallic particles embedded in an fcc Fe–Ni–Al alloy. These particles were created by means of thermal ageing. The ultrafine particles had a structure of the Ni3Al type with addition of Fe atoms. The nanoparticles were three-dimensional and had no open-volume defects at the interfaces, which could trap a positron. These observations suggest that this positron state promises to be a powerful tool for studies of mesoscopic systems in condensed matter.

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