Hiroki Sato

In this study, we examined the corrosion resistance of Ru ₅₇ Mo _14.25 W _23.75 Fe ₅ , Ru ₅₄ Mo _13.5 W _22.5 Fe ₁₀ , and Ru ₄₈ Mo ₁₂ W ₂₀ Fe ₂₀ alloys in inorganic acids. The alloys were fabricated using the dewetting micro-pulling-down and plasma-melt stamping methods. Immersion tests in H ₂ SO ₄ at 300 °C for 24 h indicated that Ru-Mo-W-Fe alloys exhibit better corrosion resistance (10 mm y ⁻¹ ). Immersion tests at 25 °C in 5% HCl for 72 h and at 100 °C in 50% HF for 24 h also indicated that Ru-Mo-W-Fe alloys are highly corrosion resistant. Electrochemical tests in 1 M HCl and 1 M H ₂ SO ₄ revealed an increase in the anodic current and the formation of a low charge transfer resistance passive layer corresponding to alloying Fe. XPS analysis revealed that the primary corrosion product formed during polarization of Ru-Mo-W-Fe alloys in 1 M H ₂ SO ₄ was WO ₃ . Notably, WO ₃ is kept passivated on pure W during the corrosion in H ₂ SO ₄ ; however, it is not kept passivated when present on Ru-Mo-W-Fe alloys.

A novel single-crystal growth method was developed, using arc plasma and metal melt, for a quick survey of high melting point materials. Single crystals of Yb-doped Lu₂O₃, Lu_0.388Hf_0.612O_1.806, and Lu_0.18Hf_0.82O_1.91, with melting points of 2460, 2900, and 2840 °C, respectively, were grown by an indirect heating method using arc plasma. We refer to this indirect heating growth method as the core heating (CH) method. The CH-grown Yb1%-doped Lu₂O₃ sample showed a full width at half maximum of 286 arcsec in the X-ray rocking curve. This value is better than the 393 arcsec obtained for the crystal grown by the micro-pulling-down (μ-PD) method. The Yb charge transfer state (CTS) emission was observed at 350 nm in the Yb1%-doped Lu₂O₃ and Lu_0.18Hf_0.82O_1.91. In the case of the μ-PD method, using a rhenium (Re) crucible, absorption due to Re contamination and a resulting reduction in the Yb CTS emission were confirmed. However, contamination did not influence the properties observed in the crystals grown by the CH method.

Ce-doped LaBr₃/AEBr₂ (AE = Mg, Ca, Sr, Ba) eutectics were grown using the Bridgman–Stockbarger (BS) method in quartz ampoules. The eutectics (AE = Mg and Ca) showed optical transparency like optical fiber bundles. A grown Ce-doped LaBr₃/MgBr₂ eutectic shows a 355 nm emission ascribed to Ce³⁺ 4f-5d transition under X-ray excitation. The smaller the ionic size of AE, the higher the light yield of the sample was. The light yield of Ce:LaBr₃/MgBr₂ was 34,300 photon/MeV, which is higher than Ce:LYSO standard. Scintillation decay time under 662 keV gamma-ray excitation was 18.8 ns.

Carbazole crystals were grown using self-seeding vertical Bridgman technique, and the scintillation properties for neutron detection were investigated. Results of powder XRD and FTIR analyses indicated the single phase of the grown carbazole crystal with orthorhombic structure. Photo- and radio- luminescence measurements were carried out, and maxima of both emission peaks were at 420 nm. The light yield under 5.5 MeV alpha-ray irradiation was estimated to be 1.87 times higher than that of lithium glass GS-20. The scintillation decay time under neutron irradiation was estimated to be 11.4 ± 0.3 ns. It follows from the temperature dependence measurements thatthe light output under 662 keV gamma-ray excitation decreases with increasing temperature.

This article presents the development of diced SrI2:Eu arrays and their scintillation properties when coupled with a multipixel photon counter (MPPC) array. Using a dicing technique specific to halide scintillators, a high-energy resolution scintillator array is developed that is cost-effective and widely applicable. The developed SrI ₂ :Eu arrays are of 3 x 3 x 3 mm3/pixel 4 x 4 matrix (TYPE1) and 1 x 1 x 1 mm ³ /pixel 9 x 9 matrix (TYPE2) structures. We fabricated test gamma-ray detector modules consisting of the TYPE1 and TYPE2 arrays coupled with an MPPC array. The mean peak to valleys ratio is 85.3 ± 14.9 for the TYPE1 array and 38.5 ± 16.6 for the TYPE2 array detector. The average energy resolutions obtained for the TYPE1 and TYPE2 gamma-ray detectors were 5.4 ± 0.4% full-width at half-maximum (FWHM) and 5.2 ± 0.6% FWHM, respectively, for 662-keV gamma-rays. The variation in the signal pulse height of the TYPE1 and TYPE2 detectors was only 10.6% and 10.4% in FWHM, respectively. These results demonstrated that the dicing technique proposed in this article could be applied to hygroscopic halide scintillators.

A novel device structure “double layered thickness-shear resonator” was proposed to improve the temperature characteristics of a bulk acoustic wave resonator. In order to design the double layered resonator, optimal combination of cut angles and thickness ratio of the substrates were determined from calculations using material constants and their temperature coefficients measured for a Ca ₃ TaGa ₃ Si ₂ O ₁₄ (CTGS) single crystal. Based on the results, a double layered resonator was fabricated by directly bonding two CTGS substrates with cut angles of 122°Y and 171°Y under the thickness ratio of 0.248. As a result, the double layered resonator operated successfully at a fundamental mode of around 7.5 MHz like a normal resonator exhibiting temperature compensation effect. The mechanism of the deviation from the expected value observed in the measured temperature dependence of the frequency changes was discussed using the model of the wave propagation and the electric field generated in the double layer structure.