Positron annihilation lifetime and coincidence Doppler broadening of annihilation radiation measurements were investigated for cold-worked Fe at deformations of up to 40%. The positron annihilation lifetime positron annihilation lifetime spectra were analyzed into 2 lifetime components. The shorter lifetimes were smaller than the monovacancy lifetimes, and were possibly caused by deformation-induced dislocations and vacancy-impurity complexes. The longer lifetimes showed that the deformation also introduced larger vacancy clusters (consisting of 5 to 10 vacancies) as a result of a cold-working. The behavior of the S-parameter (deduced from coincidence Doppler broadening of annihilation radiation) with rolling deformation was analogous to the mean positron lifetime. It increased up to 5% rolling deformation, and then levelled off. The coincidence Doppler broadening of annihilation radiation ratio curve, with respect to pure Fe, showed that - above 5% rolling deformation - the nature of the defects which trapped the positron had changed.

Vacancy-Type Defects in Cold-Worked Iron Studied using Positron Annihilation Techniques. H.F.M.Mohamed, J.Kwon, Y.M.Kim, W.Kim: Nuclear Instruments and Methods in Physics Research B, 2007, 258[2], 429-34