Positron annihilation study of voids in a neutron irradiated aluminum single crystal |
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Authors: | K. Petersen N. Thrane G. Trumpy R. W. Hendricks |
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Affiliation: | (1) Laboratory of Applied Physics II, Technical University of Denmark, DK-2800 Lyngby, Denmark;(2) Metals and Ceramics Division, Oak Ridge National Laboratory, 37830 Oak Ridge, Tennessee, USA |
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Abstract: | We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of 1.5·1021 n/cm2 (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·1014 voids/cm3 with a mean diameter of 330 ?, as determined by both small-angle x-ray scattering and transmission electron microscopy. The positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the model of a positron state at the void surface. The positron diffusion coefficient appears to have aT 1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described by a single component of 170 ps, the observed lifetime in unirradiated aluminum. Research sponsored in part by the U.S.Atomic Energy Commission under contract with the Union Carbide Corporation. |
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Keywords: | 78.70 |
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