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[en] A stress-corrosion-cracked Type 304 austenitic stainless steel was investigated by the Doppler broadening of annihilation radiation (DBAR) spectroscopy with a positron microbeam. Clear increase of S parameter was observed over 200-400 μm areas from the stress corrosion cracking (SCC) crack. From the comparison of the DBAR spectra obtained from the stress-corrosion-cracked sample and plastically deformed sample, the increase of S parameter around the SCC crack was attributed to plastic-deformation-induced vacancies.

[en] We have started the development of a spin-polarized positron beam. In order to obtain a highly spin polarized positron beam, a ⁶⁸Ge-⁶⁸Ga source will be produced using a nuclear reaction of ⁶⁹Ga(p,2n)⁶⁸Ge. The optimum proton bombardment energy for ⁶⁹Ga target is simulated to be 25 MeV using the Induced Radioactivity Analysis Code (IRAC). A newly designed ⁶⁹Ga target holder will also be used as a ⁶⁸Ge-⁶⁸Ga source capsule.

[en] Silicon-oxide-backboned hybrid thin films with thicknesses around 600 nm were fabricated through plasma enhanced chemical vapor deposition from tetraethyl orthosilicate mixed with hexamethyldisiloxane as precursors, and their subnano-scaled holes, generated by annealing at 560 °C, were investigated by means of the positron lifetime technique with a pulsed, low-energy positron beam. The hole dimension was quantified from the ortho-positronium lifetime for the as-prepared and annealed films with different compositions. The effect of the heat treatment and the precursor composition on the subnano holes was discussed.

[en] The reinforced concrete containment vessel (RCCV) is the most critical part in construction of an ABWR plant. Use of steel plate reinforced concrete (SC) and a large modular construction method are effective in shortening the construction period (Ijichi et al., 2004)1). This research is aimed at a remarkable shortening of the construction period of an ABWR plant (period from 1st concrete placement to Fuel/Loading is less than 22 months). Conceptual design of a steel plate reinforced concrete containment vessel (SCCV) using an SC structure is carried out and structural experiments are conducted. It is thus confirmed that SCCV shows outstanding structural performance, compared with RCCV. This paper outlines the study results. (authors)

[en] Highlights: ► Major sources of vacancies are the plastic deformation and the Kirkendall effect. ► Monovacancies in Type 304 stainless steels are annealed at 200–400 °C. ► The recovery temperature corresponds to the LWR operating temperature. - Abstract: To reveal vacancy formation during the stress corrosion cracking (SCC), three factors influencing SCC in Type 304 stainless steels—sensitization heat treatment, corrosion treatment and tensile plastic deformation—were investigated by means of positron annihilation spectroscopy. Vacancy defects induced by the sensitization heat treatment and by tensile deformation were identified as monovacancies. These monovacancies were annealed within the same temperature range in which light water reactors are operated (280–320 °C). The above results allow us to conclude that such vacancy defects play an important role in high-temperature-water SCC crack propagation.

[en] Effects of growth temperature and Si doping on the formation of vacancy defects in molecular beam epitaxy GaCrN films have been studied by positron annihilation spectroscopy. No vacancy defects were detected in the GaCrN films grown at 700 deg. C. In the undoped GaCrN film grown at 540 deg. C, vacancy clusters with sizes of V₈ to V₁₂ were responsible for positron trapping. Vacancy clusters were much reduced by Si doping, but complexes related to nitrogen vacancies still survived.

[en] To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L stainless steels, vacancy recovery processes were investigated by means of positron annihilation spectroscopy. Although vacancies in additive-free 316L stainless steels were mobile at 300 °C, which is a typical nuclear reactor operating temperature, vacancies in oversized elements doped 316L were stable up to 300–350 °C. This result indicates that oversized elements stabilize vacancies in stainless steels. Stability of vacancies inhibits the radiation-induced grain boundary segregation and may also lead to suppression of high-temperature water stress corrosion cracking that is observed in nuclear materials.

[en] In the field of polymer-electrolyte-membrane (PEM) fuel cell technology, the structures of free-volume holes in the PEMs are very important because they are correlated to the supplied-gas crossover phenomenon, which sometimes deteriorates the cell performance. In this study, we investigated the size and location of free-volume holes in the crosslinked-polytetrafluoroethylene (cPTFE) based radiation-grafted PEMs by positron annihilation lifetime (PAL) spectroscopy. For comparison, the base cPTFE and polystyrene grafted films were also measured. From the analysis of PAL spectra, it was found that there were free-volume holes with different radius of 0.28-0.30 nm and 0.44-0.45 nm. The smaller holes should be located in both PTFE crystallites and poly(styrene sulfonic acid) grafts, while the larger holes are considered to exist in amorphous PTFE phases.

[en] Effect of Si doping on low-temperature grown GaCrN films has been investigated by positron annihilation spectroscopy. In undoped GaCrN films grown at 540 °C, vacancy clusters with sizes of V₆–V₁₂ were found to be responsible for positron trapping. Such vacancy clusters were considerably suppressed in Si-doped GaCrN films grown at 540 °C, although divacancies (V_GaV_N) still survived. The Si-doping may be one possible way to suppress vacancy aggregation during low temperature crystal growth, and the further methods to remove divacancies are required.