Lifetime of positrons in nanostructured nonstoichiometric silver sulfide Ag$_{2-\delta}$s

The lifetime of positrons in nanostructured nonstoichiometric silver sulfide Ag$_{2-\delta}$S samples with average nanoparticle sizes from 44 to 230 nm has been measured. It has been found that the lifetime spectra of Ag$_{2-\delta}$S nanoparticles include two components corresponding to the capture and annihilation of positrons in two types of defects: structural vacancies of the metallic sublattice and vacancy clusters at the interfaces between nanoparticles. The long surface component depends on the size of silver sulfide particles and indicates a difference in their defect structure.