Evaluations of pure and ytterbium doped transparent ceramic complex perovskite scintillators

Optical and scintillation properties of complex perovskite transparent ceramic scintillators of pure and Yb³⁺ doped Ba(ZrMgTa)O₃ and (LaSr)(AlTa)O₃ ceramics are reported. The materials were produced by Murata Manufacturing. Their optical properties including transmittance and photoluminescence spectra were evaluated. The ceramics demonstrated high transparency (50–70%) in visible wavelength region. Additionally, strong emission peaks were observed at 470 nm in Ba(ZrMgTa)O₃ under 284 nm excitation and at 500 nm in (LaSr)(AlTa)O₃ under 324 nm excitation. The photoluminescence decay times of Ba(ZrMgTa)O₃ and (LaSr)(AlTa)O₃ samples were 14 and 16 μs, respectively. Judging from these optical properties, Yb³⁺ emission was not observed in these materials. In radio luminescence spectra, all specimens exhibited the same emission peaks with relatively higher emission intensity. ²⁴¹Am 5.5 MeV α-ray induced pulse height spectra of the samples were also measured, and (LaSr)(AlTa)O₃ demonstrated ～500 ph/5.5 MeV α with 10 μs shaping time constant.     

Humidity sensing properties of CU_2O-PEPC nanocomposite films

正A blend of copper oxide nanopowder(Cu_2O),3 wt.%,and poly-N-epoxypropylcarbazole(PEPC), 2 wt.%,in benzol was drop-casted on glass substrates with pre-deposited surface-type silver electrodes for the fabrication of Cu_2O-PEPC nanocomposite thin films.The thicknesses of the Cu_2O-PEPC films were in the range of 10-13μm.The effect of humidity on the electrical properties of the nanocomposite films was investigated by measuring the capacitance and dissipation of the samples at two different frequencies of the applied voltage:120 Hz and 1 kHz.The AC resistance of the samples was determined from the dissipation values,and the DC resistance was measured directly.The effect of ageing on the humidity sensing properties of the nanocomposite was observed. After ageing,it was observed that at 120 Hz and 1 kHz,under a humidity of up to 86%RH,the capacitance of the cell increased by 85 and 8 times,and the resistance decreased by 345 and 157 times,accordingly,with respect to 30%RH conditions.It was found that with an increase in frequency,the capacitance and resistance of the samples decreased.It is assumed that the humidity response of the cell is associated with the diffusion of water vapors and doping of the semiconductor nanocomposite by water molecules.     

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.     

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 structure of La3MGa5O14 (M=Ti, Zr, Hf)

La₃M⁴⁺Ga₅O₁₄ (M=Ti, Zr, Hf) compounds were crystallized using the micro-pulling down and Czochralski techniques. Both growth methods showed that these three crystals are peritectic compounds. The structure of La₃TiGa₅O₁₄ (LTiG) crystal was refined using single-crystal X-ray diffraction data. LTiG was observed to be isostructural to Ca₃Ga₂Ge₄O₁₄ (P321 (No.150), Z=1) and the lattice parameters are a=8.223(1), c=5.109(1) Å. The Ti atoms were found to occupy octahedral (1a) and tetrahedral (3f) sites coordinated by six and four oxygen atoms, respectively.     

Carbon Nanotubes and Graphene Powder Based Multifunctional Pressure,Displacement and Gradient of Temperature Sensors

Semiconductors - This work presents the fabrication and investigation of the multiwalled carbon nanotubes (MWCNTs) and graphene pristine powders based multifunctional pressure, displacement and...     

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.     

Optical properties and gamma-ray response of Czochralski grown Pr:Lu3Al5O12 scintillating garnet crystals with different Pr content

Pr:LuAG single crystalline scintillators with different Pr³⁺ concentration, 0.1, 0.18, and 0.22 mol% were grown by the Czochralski method. The crystals were cut to dimensions of 2.2 × 2.2 × 15 mm³ and polished, simulating sensors for Positron Emission Tomography (PET). Their absorption coefficients were examined, and the absorption strength was found to be proportional to the Pr concentration. The α-ray induced emission spectra of the samples demonstrated two emission lines peaking at 310 and 370 nm. The emission intensities in the radio luminescence spectra were also proportional to the Pr content. The absolute light yields and intrinsic energy resolution under γ-ray irradiation were evaluated at +20, 0, and −20 °C using avalanche photodiode as a photodetector. Pr 0.22% doped crystal had strongest light output of 16 400 ph/MeV, and its intrinsic energy resolution was around few % at several hundred keV. When coupled with PMT, the decay time was around 25 ns, and it was almost independent on concentration.     

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.