Fundamental optical constants of Nd-doped Y2O3 ceramic and its scintillation characteristics

Transparent Nd:Y₂O₃ ceramics were produced by vacuum sintering. Their fundamental optical constants including optical transmittance, reflectivity, absorption coefficient, refractive index, extinction coefficient, and dielectric constant were evaluated. Scintillation characteristics including radio-luminescence and light yield under α (²⁴¹Am 5.5 MeV) excitation are reported as well.     

Multiple-Approach Evaluation of WSP Coatings Adhesion/Cohesion Strength

Adhesion/cohesion testing represents one of the most common methods for benchmarking and optimization of thermal spray coatings. However, owing to the inhomogeneous coating microstructure, such testing may be quite troublesome. In this study, adhesion/cohesion strength of representative metallic and ceramic coatings deposited by water-stabilized plasma (WSP) spraying was evaluated by four different methods: tensile adhesion test, pin test, tubular coating tensile test, and shear test. Combination of various methods enabled the evaluation of the coating adhesion/cohesion strength under different loading conditions. Limitations and benefits of each method for testing of WSP coatings are demonstrated. Dominating failure micromechanisms were determined by supplementary fractographic analysis.     

Fabrication of Metallic Fibers with High Melting Point and Poor Workability by Unidirectional Solidification

Innovative method acceptable for production of Iridium (Ir) and Ruthenium (Ru) metal fibers with high melting point and poor workability is developed using an alloy‐micro‐pulling‐down (A‐μ‐PD) method and ceramic crucibles with sufficient mechanical and thermal shock resistance. As‐grown (as‐solidified) Ir and Ru fibers are approximately 1 mm in diameter and their lengths exceed 15 and 0.3 m, respectively. Both Ir and Ru fibers are composed of number of elongated grains oriented along a growth direction, which is attributable to the unidirectional solidification. The flexibility and oxidation resistance of the Ir fiber grown by the A‐μ‐PD method is considerably improved as compared to a commercial Ir wire made by wire‐drawing process.

     

Crystal growth and scintillation properties of Ce and Eu doped LiSrAlF6

Ce and Eu doped LiSrAlF₆ (LiSAF) single crystals for the neutron detection with different dopant concentrations were grown by the micro-pulling-down method (μ-PD). In Ce:LiSAF, intense emission peaks due to Ce³⁺ 5d-4f transitions were observed at approximately 315 and 335 nm in photo- and α-ray induced radio-luminescence spectra. In case of Eu:LiSAFs, an intense emission peak at 375 nm due to Eu²⁺ 5d-4f transition was observed in the radio-luminescence spectra. The pulse height spectra and decay time profiles were measured under ²⁵²Cf neutron irradiation to examine the neutron response. The Ce 3% and Eu 2% doped LiSAF showed the highest light yield of 2860 ph/n with 19 ns main decay time component and 24,000 ph/n with 1610 ns.     

Investigations of optical and scintillation properties of Tm-doped YAlO3

Pure, 0.1, 0.5 and 1 mol% Tm-doped YAP single crystalline scintillators were grown by the μ-PD method. The XRD analysis confirmed the lattice constants decrease with the Tm concentration. In the transmittance measurement, the absorption bands due to the Tm³⁺ 4f-4f transitions were observed at 265, 360, 485, 690 and 800 nm and they were ascribed to the transition from the ³H₆ ground state to its ¹I₆, ¹D₂, ¹G₄, ³F₃ and ³H₄ excited states, respectively. Strong emission peak due to the ¹I₆-³F₄ transition of Tm³⁺ appeared at 350 nm under X-ray irradiation. The photoluminescence decay time constants related to this transition were evaluated to be from 15.3 to 17.3 μs and the scintillation decay time constants under gamma-ray excitation were estimated to be from 17.5 to 18.8 μs. The Tm 1% doped crystal exhibited the highest light yield of 15, 100 ± 1500 photons/MeV when excited by ¹³⁷Cs gamma-ray radiation.     

Basic study of Europium doped LiCaAlF6 scintillator and its capability for thermal neutron imaging application

Eu²⁺ 0.1, 0.5, 1, and 2 mol% doped LiCaAlF₆ single crystalline scintillators were grown by the micro-pulling down (μ-PD) method. Eu²⁺ 2 mol% doped LiCaAlF₆ was also prepared using the Czochralski method. In the transmittance spectra, 4f-5d absorption lines appeared around 200-220 and 290-350 nm. An intense emission at 375 nm due to Eu²⁺ 5d-4f transition was observed under ²⁴¹Am α-ray excitation. When ²⁵²Cf excited pulse height spectra were measured, Eu 2% doped one showed the highest light yield of 29,000 ph/n with 1.15 μs decay time. Using the 2 inchφ Czochralski grown one coupled with the position sensitive photomultiplier tube covered by Cd mask with various size (1, 2, 3, and 5 mm) pin holes, thermal neutron imaging was examined. As a result, the spatial resolution turned out to be better than 1 mm.     

Simulation on Thermocapillary-Driven Drop Coalescence by Hybrid Lattice Boltzmann Method

A hybrid two-phase model, incorporating lattice Boltzmann method (LBM) and finite difference method (FDM), was developed to investigate the coalescence of two drops during their thermocapillary migration. The lattice Boltzmann method with a multi-relaxation-time (MRT) collision model was applied to solve the flow field for incompressible binary fluids, and the method was implemented in an axisymmetric form. The deformation of the drop interface was captured with the phase-field theory, and the continuum surface force model (CSF) was adopted to introduce the surface tension, which depends on the temperature. Both phase-field equation and the energy equation were solved with the finite difference method. The effects of Marangoni number and Capillary numbers on the drop’s motion and coalescence were investigated.     

Scintillation properties of Ce-doped LuLiF4 and LuScBO3

The crystals of 1 mol% Ce-doped LuLiF₄ (Ce:LLF) grown by the micro-pulling down (μ-PD) method and 1 mol% Ce-doped LuScBO₃ (Ce:LSBO) grown by the conventional Czochralski (Cz) method were examined for their scintillation properties. Ce:LLF and Ce:LSBO demonstrated ∼80% transparency at wavelengths longer than 300 and 400 nm, respectively. When excited by ²⁴¹Am α-ray to obtain radioactive luminescence spectra, Ce³⁺ 5d-4f emission peaks were detected at around 320 nm for Ce:LLF and at around 380 nm for Ce:LSBO. In Ce:LSBO, the host luminescence was also observed at 260 nm. By recording pulse height spectra under γ-ray irradiation, the absolute light yield of Ce:LLF and Ce:LSBO was measured to be 3600±400 and 4200±400 ph/MeV, respectively. Decay time kinetics was also investigated using a pulse X-ray equipped streak camera system. The main component of Ce:LLF was ∼320 ns and that of Ce:LSBO was ∼31 ns. In addition, the light yield non-proportionality and energy resolution against the γ-ray energy were evaluated.     

Fabrication and characterization of large size LiF/CaF2:Eu eutectic composites with the ordered lamellar structure

As alternative candidates for the ³He neutron detectors, ⁶LiF/CaF₂:Eu eutectic composites were fabricated and their scintillation properties were evaluated. Large size LiF/CaF₂:Eu eutectic composites of 58 mm diameter and 50 mm thickness were produced by Bridgman method. The composites had a finely ordered lamellar structure along the solidification direction. The lamellar structure was controlled by the direction and the rate of solidification, and it was optimized to improve the scintillation properties. Better results were achieved when thinner lamellar layers were aligned along the scintillation light path.     

Evaluation of characterization of rare-earth doped sesquioxide ceramic scintillators

We investigated basic optical and scintillation properties of pure Y₂O₃, Tm³⁺-doped Y₂O₃, pure Lu₂O₃ and Nd³⁺-doped Lu₂O₃ transparent ceramics made by a sintering method. All ceramic samples showed 60–80% transparency, and some absorption bands due to Nd³⁺ 4f–4f transition were observed in Nd³⁺:Lu₂O₃ ceramic. Both Tm³⁺:Y₂O₃ and Nd³⁺:Lu₂O₃ ceramics showed sharp luminescence lines corresponding to the 4f–4f transition under 285 nm (Tm³⁺:Y₂O₃) and 340 nm (Nd³⁺:Lu₂O₃) excitation. The photoluminescence decay times were calculated to be about 24 μs for Tm³⁺:Y₂O₃ and 1 μs for Nd³⁺:Lu₂O₃, respectively. In radioluminescence measurements, Tm³⁺ and Nd³⁺ 4f–4f luminescence were observed for Tm³⁺-doped Y₂O₃ and Nd³⁺-doped Lu₂O₃ ceramics under ²⁴¹Am 5.5 MeV α-ray excitation. Finally scintillation light yield was investigated with pulse height analysis.