In-beam studies of defect cascades in metals

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Abstract

The PAD method allows the investigation of recoil-induced defect cascades during the first 10 −9−10 −5 s after their production by nuclear reactions. A short review of experimental results and their interpretation is given. Recent very accurate measurements of 69Ge in a 66Zn single crystal performed in the temperature range between 25 K and 580 K allow one to draw conclusions concerning the dynamical rearrangement of the radiation damage in the vicinity of the primary recoil atom. The measured spectra for temperatures below 500 K deviate from the modulation pattern expected for static defect distributions around the probe atoms. This proves that the temperature dependence of the fraction of probe atoms located at unperturbed substitutional lattice sites has to be explained in terms of trapping and detrapping of defects. No distinct defect induced quadrupole interaction frequency could be resolved. The increase in the observed anisotropy between 400 K and 500 K is analyzed in the framework of a new extended model for detrapping processes in noncubic metals. This model reproduces the observed temperature dependence of the different harmonics of the perturbation function. It is shown that the center of the efg distribution caused by the trapped defects is shifted to a value close to zero. It thus deviates significantly from the value of the substitutional lattice site. The dissolution energy of the probe-defect complex was deduced to be 0.54(5) eV.

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