Fig. 1. Schematic illustration of positron annihilation observables measured by LT and CDB spectroscopy.

Fig. 2. An example of LT spectrum measured on plastically deformed steel. Fit of the spectrum is plotted by a thick solid line. The spectrum consists of a free positron component with lifetime τ1 = (15 ± 2) ps and a contribution of positrons trapped at dislocations with lifetime τ2 = (154 ± 1) ps. The source contribution is plotted by dotted lines and consists of two components representing a contribution of positrons annihilating in the source spot and the covering foil. Residuals expressed in units of one standard deviation are plotted in the upper panel.

Fig. 3. An example of two-dimensional CDB spectrum measured for a well annealed pure Fe.

Fig. 4. An example of horizontal and vertical cut from two-dimensional CDB spectrum in Fig. 3. The horizontal cut plotted by open circles represents Doppler broadened (DB) profile. The vertical cut plotted by solid line corresponds to resolution function of spectrometer. The width of the band used for the horizontal and vertical cut was ± 5 keV.

Fig. 5. Positron density in the (001) plane for Cu calculated by ATSUP-LDA approach: (a) perfect crystal, (b) mono-vacancy, (c) di-vacancy, (d) tri-vacancy. Positions of Cu ions are indicated by full circles. Lengths are given in the units of the lattice parameter.

Fig. 6. CDB ratio curves (related to pure Fe) for quenched Fe3Al alloy and pure Al reference [106].

Fig. 7. Results of LT spectroscopy for quenched Fe3Al alloy subjected to isochronal annealing: (a) lifetimes of components resolved in LT spectra; (b) intensity of positrons trapped at vacancies [106].

Fig. 8. Arrhenius plot for Fe3Al alloy: a logarithm of vacancy concentration determined by LT spectroscopy for temperatures above 500 °C plotted as a function of 1/kT[106].

Fig. 9. Calculated dependence of the positron lifetime on the size of vacancy clusters consisting of NV vacancies for α-Fe.

Fig. 10. The size distribution of vacancy clusters in ultrafine grained (UFG) metals prepared by HPT [110].

Fig. 11. (a) The lowest energy hydrogen sites around vacancy in Nb obtained by ab-initio theoretical calculations [134]. The positions of H atoms are denoted by small purple circles, crosses indicate the octahedral interstitial sites and large blue circles denote Nb atoms; (b) dependence of the lifetimes of positrons trapped at vacancies on the number of hydrogen atoms bound to vacancy. Results of theoretical calculations are plotted by full circles. The lifetime of trapped positrons measured in hydrogen loaded Nb is plotted by an open star. Dotted line indicates the bulk positron lifetime for Nb.

Fig. 12. Positron density in the (001) plane for Nb obtained by theoretical calculations: (a) plain vacancy; (b) vacancy associated with single H atom; (c) vacancy associated with two H atoms; (d) vacancy associated with four H atoms. The positions of Nb atoms are indicated by larger full blue circles, positions of hydrogen atoms are denoted by smaller full purple circles.

Fig. 13. TEM bright field micrograph of HPT-deformed (a) Mg-10wt%Gd alloy containing uniform distribution of tangled dislocations, (b) IF steel with cellular dislocation structure.

Fig. 14. Schematic depiction of geometry used in DTM: a spherical dislocation cell with diameter d surrounded by a dislocation wall with thickness δ.

Fig. 15. Mean dislocation density (a) and the average size of crystallites (dislocation cells) (b) in UFG IF steel prepared by HPT plotted as a function of the equivalent strain. The results determined by PAS (using DTM) and by XLPA are compared [175].

Fig. 16. (a) Doppler broadened annihilation photo-peaks measured by CDB and corresponding to momentum distribution of annihilating pairs. The CDB curves for the as-drawn pearlitic steel wire and the wire annealed at 400 °C are compared. The CDB curves for positrons trapped at defects in pure iron, mFe,D(p), and pure carbon, mC,D(p), are plotted in the figure as well. The peaks were normalized to the same area. Since the peaks are symmetrical with respect to zero only the part corresponding to positive Doppler shifts is plotted in the figure. (b) The CDB ratio curves related to pure Fe for the steel wire in the as-drawn state and after annealing at 400 °C. The ratio curve for pure C is plotted in the figure as well. Solid lines are model curves calculated by Eq. (62) with ξC,D, as fitting parameter.

Fig. 17. (a) The development of CDB ratio curves for the pearlitic steel wire with the annealing temperature Tann. (b) The fraction ξC,D of positrons annihilated the steel wire in the vicinity of C solutes plotted as a function of annealing temperature.

Fig. 18. The ratio I2/I1 of the intensities of the components arising from positrons trapped at defects associated with GBs, namely vacancy clusters at triple points (I2) and vacancy-like misfit defects distributed along GBs (I1). The ratio I2/I1 is plotted as a function of the inverse of square of the grain size, 1/d2. The average grain size d was determined by XRD. The figure shows results obtained for zirconia-based nano-powders prepared by co-precipitation [197,207].

Fig. 19. Schematic depiction of various kinds of precipitates (upper panels) and positron potential and density across the precipitate. (a) defect-free coherent precipitate ΔEP,M+<0, (b) defect-free coherent precipitate ΔEP,M+>0, (c) coherent precipitate ΔEP,M+>0 containing open volume defects, (d) semi-coherent precipitate, (e) incoherent precipitate, (f) incoherent precipitate containing open volume defects in its interior.

Fig. 20. The CDB ratio curves (related to non-irradiated steel) for reactor pressure vessel steel neutron irradiated in a nuclear power plant for 10 years (open blue circles) and subjected to post-irradiation annealing at 400 °C (full red circles) and 600 °C (open green squares). Ratio curve for pure Cu reference is plotted in the figure as well (brown open triangles).

Fig. 21. A color coded map of the development of CDB ratio curves for reactor pressure vessel steel neutron irradiated for 10 years in a nuclear power plant and subjected to isochronal annealing [231]. The ratio curves were always related to non-irradiated steel.