Positrons may be used in many cases to determine defect densities of vacancies and dislocations. In case of saturated positron trapping, i.e. all positrons were getting trapped, only a lower-limit estimation could be given. However, a combination of positron back-diffusion measurements using a mono-energetic positron beam in combination with conventional lifetime spectroscopy could be used to overcome the problem of saturated positron trapping. As a case study, this combination was used for the determination of dislocation densities in polycrystalline Ni samples of highly varying dislocation density. Saturated positron trapping into dislocations and small voids was observed. The total positron trapping rate was calculated from the positron diffusion length obtained by back-diffusion experiments. The trapping rates of the two defects were finally obtained using the decomposition of lifetime spectra. The results were found in good agreement with those determined by the analysis of synchrotron Bragg-diffraction profiles, measured on the same set of samples. From the comparison of both techniques, the positron trapping coefficient was found to be μdisl = 3.9cm2/s for a high density of dislocations in Ni.

Determination of Absolute Defect Concentrations for Saturated Positron Trapping – Deformed Polycrystalline Ni as a Case Study. R.Krause-Rehberg, V.Bondarenko, E.Thiele, R.Klemm, N.Schell: Nuclear Instruments and Methods in Physics Research B, 2005, 240[3], 719-25