Elektronenbestrahlungsexperimente an Tantal

Abstract

Abstract In high purity Ta-foils the damage production during electron irradiation at 4.5 °K has been studied using electrical resistivity measurements. The observed dose curves show a strong saturation effect, i. e., the effective damage rates decrease with increasing defect densities. Two mechanisms contribute to this radiation annealing effect: 1) Spontaneous recombination of newly produced interstitials or vacancies with vacancies or interstitials already present in the crystal (direct re­ combinations) and 2) spontaneous recombination of close Frenkel pairs under the influence of nearby low energy recoil events (subthreshold events). The contribution of both direct recombin­ations and subthreshold events can be separated by subthreshold test irradiations as well as by radiation doping experiments. Both methods yield mutually consistent results. From these one can deduce a value of the spontaneous recombination volume of about 50 atomic volumes and a value for the cross section for the spontaneous recombination of a close Frenkel pair by subthreshold energy transfers from 1.2 MeV electrons of about 90,000 barns.