The Influence of the Initial Defect Concentration on the Annealing of Low‐Temperature Irradiated Metals

Abstract

Measurements are made of isochronal annealing in aluminium, copper, silver, and gold, after irradiation a t 4.5 O K with various doses of fast neutrons. It is shown that the relative amount of recovery within annealing stage I is reduced, and annealing stage 111 is shifted to lower temperatures with increasing defect concentration. The first observation can be explained b y the higher probability for annihilation of close Frenkel-pairs, during the radiation-annealing process, compared with the probability for recombination of more distant Frenkel-pairs. The shift with concentration of annealing stage 111 and annealing stage IE for aluminium indicates the existence of freely-migrating defects. For aluminium the existence of two freely-moving interstitials is confirmed. I n addition it is shown that the observed annealing behaviour of all the metals considered can be explained by this twointerstitial model (previously proposed by SEEGER and SOSIN) taking into account the different defect arrangements produced by low-temperature electron and neutron irradiation. Isochrone Erholungskurven von Aluminium, Kupfer, Silber und Gold nach Reaktorstrahlung bei 4,5 "K zeigen, daR mit zunehmender Dichte der durch die Bestrahlung erzeugten Defekte die Hohe von Erholungsstufe I abnimmt UndErholungsstufe 111 sich zu tieferen Temperaturen verschiebt. Ersteres kann durch die gegeniiber weiter entfernten Frenkelpaaren erhohte Reaktionswahrscheinlichkeit von eng benachbarten Frenkelpaaren bei den wahrend der Bestrahlung ablaufenden athermischen Rekombinationsprozessen erklart werden. Die Verschiebung der Erholungsstufe 111 sowie der Stufe IE in Aluminium mit der Ausgangsdichte der Defekte zeigt, da13 in diesen Stufen frei bewegliche Zwischengitteratome mit Leerstellen rekombinieren. Durch AusschluB aller anderen Moglichkeiten wird fur Aluminium das von SEEGER und SOSIN bereits friiher geforderte Modell zweier frei beweglicher Zwischengitteratome bewiesen. Ferner wird gezeigt, wie dieses Modell auch das Erholungsverhalten der anderen Metalle gut erklart, wenn man nur die verschiedene raumliche Anordnung der Defekte nach Elektronen-und Neutronenbestrahlung berucksichtigt.Copper, silver, gold, and aluminium were irradiated at 4.5 O K up to various doses of fast neutrons in the low-temperature irradiation facility of the FRM [l].Subsequent to the irradiation the annealing behaviour of the electrical resistivity change was investigated. Because of difficulties connected w-ith the temperature control of the helium gas stream used to heat the samples, no exact isochronal annealing program could be performed. Thus it was not possible to achieve annealing periods longer than the time required to heat the samples to the desired temperature. Isochronal annealing curves found under these conditions are shown in Fig. 1 to 4. Ail these curves exhibit the structure well-known, for example, from the experiments of BLEWITT [2]. I n addition one can clearly recognize the influence of the initial defect concentration upon the subsequent recovery of the...

Influence of Neutron Irradiation at Low Temperature on Internal Friction and Bulk Modulus of Silver

“…Using the residual electrical resistivity per unit concentration of Frenkel defects in silver = = (250 f 50) pQcm [12] (compare also the values for aluminium, copper, platinum, and gold in [13]) we find a change in the concentration of Frenkel defects between the two measurements mentioned above :…”

Radiation Damage in Metals

“…This is partly explained by the recombination of newly created defects with those produced previously [126], although other mechanisms like formation of defect clusters might also contribute. For room temperature irradiations of copper alloys with 14 MeV neutrons non-linear increases of defect densities were observed [127], which follow approximately a √ φt dependence 113 Downloaded by [University of Otago] at 20: 36 25 December 2014 up to fluences of φt ∼ 10 17 n cm −2 .…”

Thermal Neutron damage in cadmium

“…(7) to the data we note that z = A p / p~, which assumes that p~ is independent of Frenkel pair configuration. Since PF = pc/N, then z = S(dp)/p,.…”