The spatial distribution of self-interstitial atoms around depleted zones in tungsten ion-irradiated at 10 K

The three-dimensional spatial distribution of self-interstial atoms (SIAs) around depleted zones (DZs) in ion-irradiated tungsten was determined by field-ion microscopy (FIM). High-purity, four-pass zone-refined, single crystal tungsten- FIM specimens were irradiated in situ with 30 keV Cr⁺ or 18 keV Au⁺ ions along the [741] direction, at 10 K, and examined at this temperature by the pulse-field-evaporation technique. At 10 K the SIAs in tungsten are completely immobile. The distances were measured along the close-packed crystallographic directions—that is, the ⟨100⟩, ⟨110⟩ and ⟨111⟩ directions—between each SIA and the DZs. Distance measurements were also made between each SIA and the irradiated surface of the specimen. The set of distances employed for analysis corresponded to the minimum measured distances; thus, the histograms of the distances presented represent a lower bound (denoted by R_min) to the actual propagation distances. For the 30 keV Cr⁺ ion-irradiated specimen a total of 97 SIAs were detected and ⟨R_min⟩ is 175 ± 110 Å; the ± values for ⟨R_min⟩ represent one standard deviation. In the case of the 18 keV Au⁺ irradiated specimen the quantity ⟨R_min⟩ is 175 ± 130 Å; 33 SIAs were detected. A composite distribution of R_min values was obtained by combining our earlier measurements (Beavan, Scanlan and Seidman 1971) with the present results to obtain ⟨R_min⟩ 160 ± 120 Å. It is suggested that this value may represent an overestimate of the mean range of replacement collision sequences in tungsten. Nevertheless, the results constitute very direct evidence for the existence of RCSs in tungsten.