Takeo Aruga

Swelling behavior of F82H steel irradiated by triple/dual ion beams

Abstract Irradiations for spallation target vessels and structural materials of fusion reactors were simulated using simultaneous triple/dual ion beams consisting of Fe 3+ , He + and H + ions or Fe 3+ and He + ions at temperatures between 470 and 600 °C to 50 dpa. The swelling of F82H (Fe–8Cr–2W–0.2V–0.04Ta–0.1C) martensitic steel was enhanced by a synergistic effect of displacement damage and the implantation of helium and hydrogen. The maximum swelling of F82H steel was 3.2% at 470 °C under a simulation of structural materials of fusion reactors, and was higher than 1.2%, which applied to a simulation of spallation target vessel. The swelling under a simulation of fusion reactor decreased with increasing irradiation temperature, however the swelling under a simulation of spallation target vessel was again increased at 600 °C by the high helium concentration. From the microstructural analysis of taking account of cavity growth process, the cause of the enhancement of swelling under a simulation of fusion reactor is thought to be gas pressure of hydrogen and helium in cavities during irradiation. The effects of 50% cold-working and carbon implantation on swelling behavior were also examined. The swelling was reduced from 3.2% to 1.4% by 50% cold-working, and to 0.5% by carbon implantation.

Effect of triple ion beams in ferritic/martensitic steel on swelling behavior

Abstract The synergistic effects of displacement damage and atomic hydrogen and helium on swelling of the ferritic/martensitic steel, F82H, has been investigated. The irradiation was performed at temperatures between 470 and 600 °C to 50 dpa (displacement per atoms) under conditions of simultaneous ion beams consisting of Fe3+, He+ and H+ ions or Fe3+ and He+ ions. The swelling of F82H steel under triple beams with 18 appm He/dpa and 70 appm H/dpa was larger than that under dual beams with 18 appm He/dpa. The swelling in F82H under triple beams increased with decreasing irradiation temperature from 0.1% to 3.2%, while swelling under dual beams was between 0.04% and 0.08%. On the other hand, in the case of triple beam irradiation with a high ratio of gas/dpa, the swelling tended to increase with irradiation temperature. The swelling in ferritic/martensitic steels is significantly enhanced by the synergistic effect of displacement damage, hydrogen and helium atoms.

Computer simulation of damage depth profiles for 2–7.5 MeV/amu heavy ions incident on pure metals with experimental comparisons

Abstract A computer code EDEP-1 was extended to a high energy region using currently reliable stopping powers. The damage depth profiles calculated for pure metals for Al, Fe, Ni, Cu, Ag, and Ta irradiated with 2–7.5 MeV/amu heavy ions of C, Cl and Cr show that the extended code gives nearly similar profiles and depths of peak damage to those obtained by a Monte Carlo calculation code, TRIM85. The discrepancies from the experimental peak depths are less than 15%. The damage stragglings around the peak are calculated to be much smaller than the experimental values.

Amorphization behaviors in polycrystalline alumina irradiated with energetic iodine ions

Abstract A cross-sectional transmission electron microscopy (XTEM) technique utilized in examining the sintered alumina (Al2O3) sample irradiated by 85.0 MeV iodine ions I7+ to 2.8×10 18 m −2 reveals that almost complete amorphization takes place up to depths around 2 μm. Several grains including grains about to be fading out at depths of 2.5–3.5 μm are seen to have moved from the yet-amorphized region leaving the amorphized region behind. The amorphized regions extend up to depths around 4.5 μm for the sample irradiated to 12×10 18 m −2 . Any defect clusters cannot be observed in grains located at depths around 8 μm, where nuclear energy depositions are predicted to peak to about 1 dpa. The present results clearly demonstrate that the energy depositions through electronic process in alumina irradiated with heavy ions like present I7+ transform the crystalline phase into amorphous ones even near room temperatures, for accumulated electronic energy depositions above some 1.5–2 GGy with deposition rates above 4–5 keV/nm/ion.

Damage distribution of heavy-ion irradiation in metals studied by electrical resistivity measurement

Abstract The stacked thin foil samples were irradiated by heavy-ions of C, Cl and Br with energies of 90–160 MeV at a low temperature below liquid nitrogen temperature, and the depth profiles of damage were obtained from the electrical resistivity change by isochronal annealing in the foils of pure Al, Fe, Ni, Cu, Ag and Ta set at various depths from an ion bombarded surface. The difference between the experimental damage peak depth and the theoretical one calculated by the modified EDEP-1 and TRIM codes is studied in terms of atomic number of irradiated metals. The half-value width of the damage distribution obtained from the experiment is larger than the calculated half-value width in the samples irradiated with C, Cl and Br ions.

Depth profiles of defects in Ar-iondashirradiated steels determined by a least-squares fit of S parameters from variable-energy positron annihilation

Abstract Using a new method for reconstructing the depth profile of defects in an iondashirradiated sample by using slow positrons, the depth profiles of vacancy-type defects in 316 stainless steel samples, irradiated with 250 keV Ar ions to a dose of 7.5 × 10 19 m −2 at room temperature, have been calculated from Doppler-broadening S parameters measured as a function of positron energies up to 16 keV. Without assuming any type of shape for the defect profiles, such as Gaussian, the defect profiling is done using a least-squares fitting method. The resulting profile suggests that in as-irradiated 316 stainless steel samples with lower carbon content, the defect distribution peaks at a depth four times larger than that of the ion range. After annealing at a high temperature of 1253 K for 0.5 h, the fitted profile shows that the peak around the average ion range is highly enhanced. While in the steel added with 0.3 wt% titanium, the profile exhibits almost no peak after annealing at 1073 K. The results indicate that the radiationdashproduced vacancy clusters are stabilized by the implanted Ar atoms more effectively in the Ti-free steel than in the Ti-added steel.

Fission-neutron displacement cross sections in metals

Abstract The resistivity damage rates for 22 metals were measured after fission-spectrum neutron irradiation at low temperature and the experimental damage rates were compared with the theoretical calculation. The relation between the theoretical displacement cross section and the atomic weight of metals can be written by two curves; one is for fcc and hcp metals, and another is for bcc metals. On the other hand, the experimental displacement cross section versus atomic weight is shown approximately by a curve for both fcc and bcc metals, and the cross section for hcp metals deviates from the curve. The defect production efficiency is 0.3–0.4 for fcc metals and 0.6–0.8 for bcc metals.

Microstructure in vanadium irradiated by simultaneous multi-ion beam of hydrogen, helium and nickel ions

Abstract Pure vanadium was irradiated at 500 and 600 °C by either 5 MeV Ni ions (single beam) or Ni+H and He ions simultaneously. The pure vanadium was of nominal 99.8% purity. For the quantitative investigation of damage structure as a function of the depth, we utilized focused ion beam (FIB) microscopy. To preserve the surface of ion-irradiated metals, we deposited tungsten on the irradiated surface. The specimens were electro-polished to remove the damaged region by FIB. When only nickel ions were used, voids formed in the region from the surface to a depth of ∼0.5 μm when irradiated at 500 and 600 °C. However, in the region of the damage peak, voids were not observed. Needle-like precipitates of about 100 nm of length were observed for any specimen covering the full ion penetration depth. It is thought that the precipitate is a carbide. Moreover, in the specimen irradiated at 600 °C, the granular precipitates were over the region of the 1.0–1.5 μm depth. Void formation was observed over the whole ion penetration depth when the specimen was subjected to Ni+He simultaneous irradiation. Needle-like precipitates were observed.

Cross-sectional observation of damage structures in Al2O3 irradiated with multiple beams of H, He, and O ions and after annealing at 1273 K

Abstract Damage structures in a single crystal α-Al2O3 sample irradiated with triple (0.25 MeV H+, 0.6 MeV He+ and 2.4 MeV O2+) ion beams at 923 K to a peak dose of 3.6 dpa were characterized by dislocation loops distributed from the region close to the incident surface to the region of 1.8 μm in depth, with cavities being formed in the restricted region of depths from 1.2 to 1.75 μm. A similar depth profile of damage structures was formed in a sample irradiated with dual (0.25 MeV H+ and 2.4 Me V O+) ion beams to a peak dose of 10.6 dpa, except that tiny cavities were formed down to the smaller depth of 0.5 μm. Depth profiles of implanted hydrogen atoms measured through a nuclear reaction analysis revaled that point defect mobilities were largely enhanced in the presence of hydrogen without helium. Upon annealing for 1 h at 1273 K, cavities grown to 70–80 nm at the maximum size were formed around peak damage regions in both the irradiated samples. Resultant cavity swellings were 6.2% and 18%, the ratio of which was found to be equal to that of accumulated damage.

Pinning Strength of Bi–Sr–Ca–Cu–O Superconductor after Ion Irradiation

The temperature dependence of critical current was measured after removing an applied magnetic field in Bi-Sr-Ca-Cu-O films after He ion irradiation at room temperature. The curve was remarkably different from the temperature dependence of critical current without magnetic field. The difference between the temperature dependence of critical current after removing an applied magnetic field and without magnetic field is due to the presence of pinning denters produced by irradiation.