Abstract
AbstractWolf's general theory of rotating‐frame nuclear spin‐lattice relaxation is applied to the effect caused by dislocations moving at an average velocity v. Equations are presented for the dependence of the NMR relaxation rate R on the mean waiting time τ of a dislocation before an obstacle, valid in both the weak‐and the strong‐collision regions. In the latter the Slichter‐Ailion‐Rowland‐Fradin theory applies. Nuclear spin relaxation tests on 23NaCl and 23NaF single crystals deformed at constant strain rates ϵ confirm the theory. The experimental data for the predicted maximum in R (reached only for NaCl at ϵm = 20 s―1) yield directly τm = 2.8 × 10―5 s, the mobile fraction of dislocations Qm/Qt = 0.26. The value of ϵm, together with the mean distance between obstacles of ≈ 2 × 10―4 cm, derived from the slope of the curve in the strong‐collision region, leads to vm = 7.1 cm s―1, corresponding to a mobile dislocation density ϱm = 1.4 × 108 cm−2.
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