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.     

Crystal growth and scintillation properties of (NaxCa1−2xLux−yNdy)F2 single crystals

Na_xCa_1−2xLu_x−yNd_yF₂ single crystals were grown from the melt using the precise atmosphere control type Micro-Pulling-Down (μ-PD) method to investigate their potential as a vacuum-ultraviolet (VUV) scintillators. The grown crystals were single-phase materials with fluorite-type structure (Fm-3m, Z = 4) as confirmed by XRD. The crystals demonstrated 80-90% transmittance above 200 nm wavelength and Nd³⁺ 5d-4f luminescence (when exited by X-ray) observed around 185 nm. The radioluminescence measurements under 5.5 MeV α-ray excitation (²⁴¹Am) demonstrated the light yield of 48 [Ph/5.5 MeV-α] and the decay time of 6.4-7.7 ns.