Energy dependence of the defect production at 78 k and 400 k in electron irradiated copper

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Abstract
Production rates of dislocation pinning points have been measured at : 8 K and 400 K in Cu irradiated with electrons of various energies between 0.25 MeV and 2.8 MeV. At 78 K the energy dependence was found to coincide exactly with the energy dependence of resistivity damage rates. At 400 K a threshold energy for pinning point production of less than 8.5 eV was found. The interstitial displacement probability P(e), however, is as small as 10−5 near this threshold. P(e) rises into the order of magnitude of 10−2 at about 15 eV. Between 20 eV and 40 eV the 400 K displacement probability is slightly enhanced when compared with the 78 K one. The lowered threshold energy and the enhanced displacement probability is explained by a thermally activated escape from correlated recombination of those interstitials which belong to close pairs or which recombine spontaneously at 78 K or lower temperatures.