Mamoru Kobiyama

Accumulation and recovery of defects in ion-irradiated nanocrystalline gold

Abstract Effects of 60 MeV 12 C ion irradiation on nanocrystalline gold (nano-Au) are studied. The experimental results show that the irradiation-produced defects in nano-Au are thermally unstable because of the existence of a large volume fraction of grain boundaries. This suggests a possibility of the use of nanocrystalline materials as irradiation-resistant materials.

Grain size measurement of nanocrystalline gold by X-ray diffraction method

Abstract The X-ray diffraction profiles on nanocrystalline gold prepared by the gas deposition method were studied by Warren-Averbach and integral breadth analysis for the evaluation of grain sizes and internal strains. The grain size of as-prepared specimens, estimated by Warren-Averbach analysis, was in the range of 7 to 20nm. The thermal stability of these specimens was found to be quite high; when annealed for 1h, the grain size remained unchanged up to 770K and grew about twice at 1070K. The root mean square strain, estimated by integral breadth analysis, was in the range of 0.8–2.3 × 10−3 and reduced to ~3 × 10−4 after annealing at 870K and higher.

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.

MAGNETIZATION OF CERAMIC Y-BA-CU-O AND BI-SR-CA-CU-O AFTER NEUTRON IRRADIATION

Magnetization of ceramic Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O superconductors was studied after neutron irradiation in the fluence from 2.4×1021/m2 to 1.8×1022/m2 at 60°C. The area of hysteresis loops was enhanced at low neutron fluence, followed by saturation and then a decrease at high fluence. In Bi-Sr-Ca-Cu-O, the degree of enhancement was smaller than in Y-Ba-Cu-O and the enhancement reached saturation at lower neutron fluence.

Sputtering of nano-crystalline gold by high energy heavy ions

In order to investigate the grain size effects and the contribution of the electronic excitation on the radiation sensitivity, we have measured the sputtering yields of nano-crystalline Au and poly-crystalline Au samples by high energy heavy ions. No meaningful difference has been observed between the sputtering yields of both samples. It also appears that the sputtering yields of both Au samples agree with those of calculation based on the linear elastic collision cascade, indicating no appreciable contribution of the electronic excitation.

Effects of He Ion Irradiation on Superconductivity of Bi-Sr-Ca-Cu-O Films

The zero resistance transition temperatures Tc (R=0) decrease remarkably from 92 K to 62 K in a Bi-Sr-Ca-Cu-O film irradiated with 400 keV He ions to a dose of 1.1×1019/m2 at room temperature. Resistivities above transition temperatures increase with increasing the dose, while transition temperatures Tc (onset) are relatively unaffected by He ion irradiations. The decrease in the transition temperatures and the resistivity increase after low-temperature irradiations at 85 K are larger than those after room temperature irradiation.

Electrical properties of neutron-irradiated oxygen potential sensors using stabilized zirconia solid electrolyte

Oxygen sensors based on zirconia solid electrolyte stabilized by MgO, CaO or Y 2 O 3 were irradiated with neutrons in the Japan Materials Testing Reactor (JMTR) of the Japan Atomic Energy Research Institute (JAERI), and the characteristics of electromotive force of these sensors under and after irradiation were measured. The electromotive force of YSZ sample decreased with increasing irradiation fluence up to 1 x 10 23 m -2 (E > I MeV). The electromotive force of the MSZ sensor irradiated for fluences up to 9 x 10 21 m -2 (E > 1 MeV) was almost equal to the reference value of the electromotive force. It was shown that after irradiation, the decrease in the electromotive force of the CSZ sensor was smaller than those of MSZ and YSZ sensors, although the electromotive forces of MSZ, CSZ and YSZ sensors were smaller than the reference value.

Critical Current and Activation Energy in Bi2Sr2Ca1Cu2Ox Films after Ion Irradiation

The temperature dependence of electric voltage in Bi2Sr2Ca1Cu2Ox films after He ion irradiation is measured for various electric currents and magnetic fields. From the thermally activated behavior of flux lines, the activation energy and the relation between the transition temperature and the Lorentz force are obtained. The pinning energy and the critical current density in Bi2Sr2Ca1Cu2Ox single-phase films decrease due to He ion irradiation.

Annealing Effects on Transition Temperature of Superconductiong Bi-Sr-Ca-Cu-O Films after Ion Irradiation

The effect of annealing after irradiation on the transition temperature is studied for polycrystalline Bi-Sr-Ca-Cu-O films irradiated by He ions at room temperature. The temperatures of the out-diffusion and the in-diffusion of oxygen are obtained by annealing in air and a vacuum. There is a large recovery stage around 200~500°C on annealing in air after irradiation. The 110 K phase grows remarkably upon annealing at 600°C after irradiation.

Recovery of yield stress in dilute Ni alloys after electron and neutron irradiations at low temperatures

Abstract Yield stress increase due to electron and neutron irradiations at low temperatures and the isochronal annealing behaviour after the irradiations have been studied by tensile tests in seven kinds of dilute Ni alloys and pure Ni. In the electron irradiation at 78 K, the yield stress increase was remarkably large in the alloys with an undersized solute, Si, and oversized ones with large atomic size misfit, such as Au and In. Two recovery stages II (78–300 K) and III (300–450 K) appeared in the isochronal curves after the irradiation. Stage II was not found in the alloys with oversized solutes of Au, In and Mn. On the contrary, the yield stress recovery in stage III increased with atomic size of the solutes in Ni, and the maximum recovery temperature shifted to higher temperatures. Little effect of solutes on the radiation-induced yield stress increase at 78 K and isochronal annealing behaviour from 78 to 723 K were observed in the case of neutron irradiation.