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This work presents our most recent results in the development of composite scintillators using the liquid phase epitaxy growth method based on the single crystalline films and single crystals of garnet compounds for the radiation monitoring of different components of mixed ionization radiation fluxes. Such composite scintillators present two- and three-layered epitaxial structures consisting of two single crystalline films of Ce3+-doped garnets, namely, Gd3Al5–xGaxO12:Ce garnet with a Ga content of x= 1.75–2.25 as a first film layer and Tb3Al5O12:Ce garnet as a second film layer. As substrates, Gd3Al5–xGaxO12:Ce single crystals with fixed Ga concentrations x= 2.3, 2.5, and 3.0 were used. For the estimation of scintillation properties of the respective epitaxial structures (pulse height spectra, light yield, and scintillation decay kinetics), we have used three types of ionizing radiation: α-particles (239Pu), β-particles (90Sr + 90Y), and γ-quanta (137Cs).

Different from conventional 2D sliding ferroelectrics with polarization switchable in the out-of-plane via interlayer sliding, we show the existence of in-plane sliding ferroelectricity in a bilayer of a pentagon-based van der Waals heterostructure formed by vertically stacking an experimentally synthesized penta-PdSe2sheet and a crystal lattice well-matched penta-PtSe2sheet. From the 128 sliding patterns, four stable configurations are found that exhibit in-plane sliding ferroelectricity with an ultralow polarization switching barrier of 1.91 meV/atom and a high ferroelectric polarization of ±17.11 × 10–10C m–1. Following the ferroelectric transition among the stable sliding configurations, significant changes in carrier mobility, electrical conductivity, and second harmonic generation are identified. In particular, the ferroelectric stacking configurations are found to possess a negative Poisson’s ratio, facilitating the experimental characterization of the sliding ferroelectric effect. This study demonstrates that pentagonal sheets can be used to realize 2D in-plane sliding ferroelectrics going beyond the existing ones.

Nearly ideal vertical AlxGa $_{{1}-{x}}\text{N}$ ( ${0.7} \leq {x} < {1.0}$ ) p-n diodes are fabricated on an aluminum nitride (AlN) substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity doping, to overcome the major bottleneck of AlN-based material: the control of conductivity. Capacitance-voltage measurements revealed that the net charge concentration agreed well with the DPD charge concentration expected from the device layer structure. The fabricated devices exhibited a low turn-on voltage of 6.5 V, a low differential specific on-resistance of 3 $\text{M}\Omega $ cm2, electroluminescence (maximum at 5.1 eV), and an ideality factor of 2 for a wide range of temperatures (room temperature—573 K). Moreover, the breakdown electric field was 7.3 MV cm−1, which was almost twice as high as the reported critical electric field of GaN at the same doping concentration. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

The fabrication of three-dimensional (3D) nanostructures within optical materials is currently a highly sought-after capability. Achieving nanoscale structuring of media within its inner volume in 3D and with free design flexibility, high accuracy and precision is a development yet to be demonstrated. In this work, a 3D laser nanolithography technique is developed which allows producing mm-long hollow nanopores inside solid-state laser crystals and with a high degree of control of pore cross-sectional aspect ratio and size. We report an in-depth study on the formation of pores both within the non-thermal regime at which temperature is fast dissipated after each laser pulse, and for a thermally controlled regime using pulse-bursts which facilitate the formation of pores with highly circular shapes down to 1.1. We demonstrate this process for a wide range of speeds, pulse repetition rates and pulse energies, thus opening the door to a much more useful nanofabrication technique for nanophotonics. Finally, we also report the change in index of refraction that is produced at the nanoscale obtaining a positive index contrast of ∼3%. The work therefore provides a promising path towards reliable 3D nanostructuring of solid-state laser media for the flexible fabrication of large and complex structures with features sizes from the nanoscale up to the mm-scale. Moreover, due to the embedded, seamless, and monolithic nature of this technology, and since YAG crystals can sustain temperatures of up to 1900 °C and are highly chemically inert and erosion resistant, we anticipate its direct application in harsh environments.

Whole gamma imaging (WGI) is a new concept that combines PET and Compton imaging by inserting a scatter detector ring into a PET ring. We developed a WGI prototype and demonstrated 3-D tomographic Compton imaging of a 89Zr-injected mouse. However, improving the scatter detector performance, i.e., crystal pitch and energy resolution, was required for high-resolution Compton imaging. Therefore, we investigated the correlation in Geant4 simulations using 909-keV gamma rays emitted from 89Zr. Three WGI geometries consisting of the scatter detector ring with different GAGG crystal sizes ( $0.9\times 0.9\times6$ mm3, $1.45\times 1.45\times6$ mm3, and $2\times 2\times6$ mm3) were modeled. The energy resolutions were obtained experimentally for application to the simulation data. Also, the values were virtually halved and 1.5 times degraded. Simulations of a point-like source were carried out varying the pixel pitch in the scatter detector and images were reconstructed. For a source placed at the center of the system, a spatial resolution of 1.7, 1.9, and 2.3 mm was obtained with pixel pitches of 0.9, 1.45, and 2 mm, respectively. The spatial resolution of the system obtained with the 0.9-mm scatterer was improved to 1.4 mm for the halved energy resolution and it was deteriorated to 2.1 mm for the 1.5 times degraded energy resolution. In the hot-rod-like phantom simulation, 2-mm diameter rods were separated in the reconstructed images with the 0.9-mm scatterer. The separation became clearer for the halved energy resolution.

In this study, a novel thermal neutron scintillator of Tl:CsI/LiBr was developed. The eutectics were fabricated at various growth rates and investigated their scintillation properties. As a material design guideline, Tl:CsI, which has an excellent $\alpha /\gamma $ ratio, was selected as the scintillator phase to realize high light yield at the energy of $\alpha $ -rays and tritons generated by the nuclear transmutation reaction with 6Li and LiBr, which has a refractive index close to that of CsI, was selected as the neutron capture phase. Radioluminescence (RL) measurement under X-ray irradiation was also performed to obtain the emission spectrum of the eutectics. The light yield and decay time for thermal neutron were measured using 252Cf and were much higher than those of conventional scintillators for thermal neutron. Furthermore, fabricated eutectic can have the higher sensitivity to thermal neutron due to the high 6Li concentration compared to conventional single-crystal scintillators. Therefore, we have succeeded in developing a promising scintillator material.

In this study, Ce:6LiCl/LaCl3 with a high 6Li concentration was developed as a novel thermal neutron scintillator, in which Ce3+ serves as an activator for the LaCl3 phase. The Ce:6LiCl/LaCl3 eutectic was grown in a quartz ampoule (inner diameter: 4.0 mm) using the Bridgman–Stockbarger technique. The grown eutectic contained 0.038 mol/cm3 6Li, which is greater than that found in commercially available scintillators such as LiCaAlF6 single crystals and Li glass. The Ce:6LiCl/LaCl3 eutectic has a lamellar eutectic structure and is optically transparent. A 350-nm emission due to Ce3+ 4f–5d transition was observed. The light yield under neutron irradiation was estimated to be 5.0 times higher than that of Li glass. In this eutectic, the 6Li ( $n$ , $a)~^{3}\text{H}$ reaction made the 6LiCl phase to act as the neutron capture phase and LaCl3 to act as the scintillator phase.

ABSTRACTImaging of 14C outside of the subject is considered to be difficult because it is a radionuclide that emits only low-energy beta particles. However, we found that bremsstrahlung X-rays form 14C could be imaged from outside of subjects and is thus applicable to in vivo small animal imaging. We developed a high-resolution low-energy X-ray imaging system using a (Gd, La)2Si2O7:Ce(La-GPS) plate combined with a flat panel photomultiplier tube (FP-PMT) for in vivo imaging of a mouse to detect the X-rays from a 14C solution administered. Without using a parallel hole collimator, accumulated 14C in the mouse’s abdomen was imaged in 1 min and dynamic in vivo imaging was possible although the spatial resolution was moderate. With a parallel hole collimator, 14C in the abdomen was obtained with a higher spatial resolution with a 60-min acquisition time. We conclude that in vivo imaging of 14C is possible by using the developed high-resolution La-GPS imaging system and may be promising for molecular imaging research.

AlLB14(L=Li or Na or K) crystals were grown using LiF or NaF or KF and crystalline boron powders as the starting materials using a high-temperature Al melt at soaking temperature 1573 ∼ 1773 K for a soaking time of 5 h under an Ar atmosphere. AlLiB14and AlNaB14crystals were obtained from LiF or NaF and B powders, and the atomic ratios (n=B/L= 2.0 ∼ 4.0) of starting materials. The AlKB14crystal was not obtained from KF and B powders as starting materials. The micro-Vickers hardness of AlLB14crystals is 24(±1) GPa for AlLiB14and 25(±1) GPa for AlNaB14. The oxidation initiation temperature of AlLiB14was about 815 K, and the peak due to the exothermic reaction was about 960 K for AlLiB14and about 990 K for AlNaB14. The final oxidation products were Li2B2O4, Al4B2O9, B2O3, and amorphous phases. The values for the electrical resistivity of the AlLB14compound were 2.4 ∼ 157 Ω·cm.

Silicon photomultiplier (SiPM)-based scintillation detectors are widely used for positron emission tomography (PET), but their application to Compton cameras should be further explored. Whole gamma imaging (WGI) is a combination of PET and a Compton camera realized by inserting a scatter detector ring into a PET ring. In a previous study, we developed a WGI prototype in which the scatter detector consists of Gd3Al2Ga3O12:Ce (GAGG) scintillators coupled with SiPM for a proof of concept. However, its Compton imaging performance was not as good as its PET imaging performance. In this article, we developed a two-layer staggered GAGG scatter detector which was optimized for WGI. GAGG crystals 1.45 ${\times }$ 1.45 ${\times }$ 4.5 mm3 in size were arranged into a 13 ${\times }$ 13 array for the 1st layer and a 14 ${\times }$ 14 array for the 2nd layer with a staggered arrangement. The two-layer crystal block was optically coupled to an 8 ${\times }$ 8 SiPM array (3-mm pixel). Using radioactive sources with different energies, we investigated the energy resolution performance experimentally. Almost all crystals were clearly separated in the flood histogram at multiple energies. The developed detector showed energy resolutions of 7.7%–8.5% at 511 keV, which was better than that of the detector of the current WGI prototype. The next-generation WGI system was modeled in simulations using the obtained energy resolution data. The simulation results showed that the WGI with the developed detector had 1.2 times better sensitivity and better angular resolution in the peripheral region than the current WGI prototype.

In this study, a 21 nm thick GaN layer with a single-step terrace surface was pseudomorphically grown on an AlN single-crystal substrate using metal organic vapor phase epitaxy by increasing the growth rate up to 1 μm h−1at a growth temperature of 850 °C and a reactor pressure of 5 kPa. The growth temperature and rate were found to be the factors dominating the flatness and coverage of the thin-GaN layer, revealing that controlling the degree of Ga migration is crucial. Furthermore, threading dislocations was not observed for the thin-GaN layer, with a flat surface, grown on the AlN substrate.

A calculation model for predicting the temperature characteristics of the double-layered resonator (DRL) was developed by using the total strain ratio including the influence of the waves reflected at the bonding boundary. The validity of the model proposed was examined from the comparison between the measured and calculated results for a DRL specimen consisting of 129.55°Y- and 0°Y-quartz substrates. The calculation results of the model proposed demonstrated that it is possible to predict the trends of changes in experimental values of temperature characteristics not only in the 1st-order mode but also in the higher-order modes. In addition, the changes in the particle displacement distribution and temperature characteristics of the DLR obtained by the model proposed were also in good agreement with the results of finite element method analysis. The proposed model is expected to greatly contribute to the design of DLRs with high excitation efficiency and excellent temperature characteristics.

The growth of Er-doped La2Hf2O7(LHO:Er) single crystals with a high mp of 2413 °C was achieved by the melt-growth method using a tungsten (W) crucible. Polished LHO:Er specimens were obtained from the as-grown crystals. The full width at half maximum of the X-ray Rocking curve on the (222) diffraction peak was 599 arcsec, and the crystals have relatively low crystallinity. The photoluminescence spectra of the polished LHO:Er specimen showed emission peaks originating from the Er3+ions in both the visible and IR wavelength ranges. It also exhibited scintillation light under X-ray irradiation.

Single -crystal growth of Tm3+-doped Y2O3, Sc2O3, and Lu2O3sesquioxides, with a melting point around 2400 °C, by the micropulling down technique is reported. Crystal quality and composition of the crystals were evaluated by rocking curve and energy-dispersive X-ray (EDX) analyses, respectively. Optical properties including optical transmittance and photoluminescence decay profiles were also examined. Furthermore, scintillation performance of the crystals including pulse height spectra and radio-luminescence spectra under α-ray and γ-ray excitation was evaluated.

We propose a scheme for imaging mid-infrared (MIR) wavelengths via pre-excitation-assisted up-conversion luminescence in lanthanide ion (Ln^3+)-doped Self-organizing Optical FIber Array (SOFIA) crystal. First, near-infrared pre-excitation wavelength excites an electron from the ground state to an excited state of Ln^3+. Next, the MIR wavelength to be imaged promotes this excited electron to a higher-lying energy state. Finally, relaxation of the electron from the higher-lying energy state to the ground state emits the up-conversion luminescence in the visible region, completing the MIR-to-visible wavelength conversion. An analysis of the 4f to 4f intra-configurational energy level transitions in Ln^3+, together with an appropriate selection of the pre-excitation wavelength and the visible luminescence constrained within the 500–700 nm wavelength range, reveals that trivalent erbium (Er^3+), thulium (Tm^3+), holmium (Ho^3+), and neodymium (Nd^3+) can be used to image MIR wavelengths. Our proposed scheme, called MIR imAging through up-Conversion LuminEscence in a SOFIA crystal, will enable the imaging of MIR wavelengths using low-cost optics and readily available silicon-based detectors in the visible spectral region and will open up new possibilities for MIR wavelength detection and imaging.

We propose a novel crystal growth method, “Core Heating (CH) Method”, which is suitable for a search of novel materials with extremely high melting points above the melting (softening) point of an Ir crucible. As a feasibility test of the novel CH method, we fabricated the conventional material, (Y0.99Ce0.01)3Al5O12(Ce:YAG), with a melting point of ∼1970 °C, because this material can be grown by the conventional melt growth technique like the micropulling down (μ-PD) method for the comparison. We compared scintillation properties for Ce:YAG prepared by the CH and μ-PD methods in order to find if the CH method can be applied to the material search. The crystals grown by both methods showed the YAG single-phase, and almost all their optical and scintillation properties of them were comparable for both samples. Particularly, the light output of Ce:YAG crystal grown by the CH method (20,000 ± 1,000 photons/MeV) was similar to that of the sample grown by the μ-PD method (23,000 ± 1,000 photons/MeV). Therefore, we concluded that the CH method is a useful technique for the search of scintillation materials with extremely high melting points.

Li2HfBr6with host emission was grown as a gamma-ray- and neutron-sensitive scintillator. Decay time of Li2HfBr6was estimated to be less than 5 μs, and single-photon counting is available to evaluate its light output. The emission wavelength under X-ray excitation was approximately 570 nm, which is a longer wavelength than that of commonly used neutron scintillators, e.g. Li-glass. The light output excited by thermal neutrons was estimated to be 52000 photons per thermal neutron, which is approximately eight to nine times higher than that of Li-glass. Additionally, neutrons and gamma rays were discriminated using the pulse-shaped discrimination technique for Li2HfBr6.

Crystals of the quaternary compounds α-Lu(Al1-xTx)B4 (T = Fe, Cr) (YCrB4-type, orthorhombic, Pbam), obtained from the nominal composition of Lu(Al1-xTx)B3, were grown by using Al flux mixed with T metal at 1773 K for 5 h under an Ar atmosphere. The maximum dimensions and morphology of the crystals obtained were about 0.7 mm × 0.5 mm for flake-type crystals of Lu(Al1-xCrx)B4 and about 5.2 mm × 0.2 mm for prism crystals of Lu(Al1-xFex)B4. The lattice constants determination and chemical analyses of Lu(Al1-xTx)B4 (T = Fe, Cr) compounds were carried out for Fe 0.5 - 10.0 at% and Cr 0.5 - 1.0 at%. The lattice constants and the unit lattice volume in Lu(Al1-xTx)B4 crystals decreased with increase of the concentration of Fe or Cr. The values of micro-Vickers hardness of Lu(Al1-xFex)B4 (x = 0.005 - 0.030) and Lu(Al1-xCrx)B4 (x = 0.005 - 0.010) samples are in the ranges of 16(2) - 20(3) GPa and 13(2) - 16(3) GPa, respectively. The hardness values showed a little increase as the solid solution of Fe or Cr was realized in Lu(Al1-xTx)B4, possibly because of distortion to the crystal structure. The magnetic susceptibility of as-grown Lu(Al0.995Fe0.005)B4 crystals for example, exhibited diamagnetic behavior with a small ferromagnetic component.

Acoustic properties of Ga–Sn–Zn (GSZ) liquid alloy coupler with high acoustic impedance were investigated to evaluate materials with high acoustic impedance. GSZ liquid alloy was prepared and its longitudinal wave velocity and attenuation coefficient were measured using the plane-wave ultrasonic material characterization system. Density of the GSZ liquid alloy was also measured by a constant volume expansion method. The acoustic impedance of the GSZ was 12 times higher than that of the water. Attenuation coefficient of GSZ is much smaller than that of water, exhibiting 7.6 dB mm−1for water and 0.5 dB mm−1for GSZ at 200 MHz. Considering the reflection and transmission coefficients at each medium boundary calculated from the experimentally obtained acoustic impedance, it was suggested that the amplitude of the reflected wave from the back surface of the Ir sample can be made about 30 times larger with the GSZ coupler than with the water coupler.

A quasibinary system of Ga2O3-Al2O3offers a range of applications in wide bandgap semiconductor engineering. Different polymorphs and concentrations of (AlxGa1−x)2O3manifest a variety of structural and electronic properties, paving the way for tunability of (AlxGa1−x)2O3for specific functions. In this work, we investigate the energetics of alpha (α) and beta (β) polymorphs of Ga2O3and Al2O3by considering all possible configurations in a conventional unit cell. Using density functional theory, we show that the formation energies of (AlxGa1−x)2O3in αand βconfigurations start to coincide at 50% concentration (Al0.5Ga0.5)2O3. The corundum configuration then becomes more dominant (lower in energy) than its monoclinic counterpart at around 80% Al concentration. The lowest formation energy configurations for 50% concentration in both αand βpolymorphs also manifest a preference towards an ordered phase. These show that the stability of Ga2O3-Al2O3and its phase transitions are significantly influenced by the relative arrangements of Ga and Al within the quasibinary semiconducting crystal.

In this study, optical-guiding crystal scintillator (OCS) and bundled plates were fabricated. Considering the performance and melting point of halide scintillators and the softening point of glass, Tl:CsI was selected as the fiber core and borosilicate glass as the cladding. Thus, the fabricated OCS had a scintillator in the core and glass in the cladding. The scintillator was remelted and unidirectionally solidified to remove the voids in the OCS and form a single crystal. Consequently, the OCS served as a scintillator fiber with excellent optical-guiding performance and high sensitivity to γ- and X-rays. An OCS plate was also fabricated using bundles of OCSs with diameters of several tens of microns. The developed OCS plate is expected to be a high-resolution and high-sensitivity imaging plate because of its excellent optical-guiding performance.

The intrinsic spatial resolution of the detector is an important aspect to reconstruct high quality nuclear medicine images. In order to realize a high spatial resolution, small pixelated Cerium doped Gd3Al2Ga3O12 (Ce:GAGG) scintillators–known for their high light output, high density and relatively fast decay time, were coupled to a digital silicon photomultiplier (dSiPM) for read out. This detector module consists of a $ {24 \times 24}$ Ce:GAGG scintillator block of 0.4 mm $ {\times }0.4$ mm $ {\times }5$ mm crystal elements and a 2 mm thick light guide made of acrylic resin. The digital silicon photomultiplier (dSiPM), DPC-3200-22-44, was used to acquire 2-D position histogram, energy resolution and coincidence timing resolution. The 2-dimensional position histogram of the Ce:GAGG block detector irradiated with 22Na gamma photons showed that most pixels were clearly resolved with an average peak-to-valley (P/V) ratio of ~3.4. The average energy resolution of the Ce:GAGG block detector was 17.8%. At trigger scheme 1 ( $ {1}^{\mathrm {st}}$ photon trigger), the coincidence timing resolution was 342 ± 7 ps FHWM when acquired in coincidence with a 2 mm $ {\times }2$ mm $ {\times }6$ mm LSO crystal (after skew correction). This study demonstrates that a pixelated Ce:GAGG block coupled with dSiPM provides good position performance and time resolution. We conclude that the highly pixelated Ce:GAGG detector module may be a good candidate for implementing ultrahigh resolution nuclear medicine systems and applications requiring good timing resolution.

During exercise, tidal volume initially contributes to ventilatory responses more than respiratory frequency, and respiratory frequency then increases rapidly while tidal volume stabilizes. Dyspnea intensity is also known to increase in a threshold-like manner. We tested the possibility that the threshold of tachypneic breathing is equal to that of dyspnea perception during cycle ergometer exercise (n= 27). Dyspnea intensity was scored by a visual analog scale. Thresholds were expressed as values of pulmonary O2uptake at each breakpoint. Dyspnea intensity and respiratory frequency started increasing rapidly once the intensity of stimuli exceeded a threshold level. The thresholds for dyspnea intensity and for occurrence of tachypnea were significantly correlated. An intraclass correlation coefficient of 0.71 and narrow limits of agreement on the Bland–Altman plot indicated a good agreement between these thresholds. These results suggest that the start of tachypneic breathing coincides with the threshold for dyspnea intensity during cycle ergometer exercise.

Scintillation properties of a flexible optical-guiding crystal scintillator with a thallium-doped CsI (Tl:CsI) crystal and borosilicate glass as the core and cladding, respectively, are reported. The as-fabricated optical-guiding crystal scintillator exhibits a light yield of 31,000 photons MeV−1under 662 keV γ-ray irradiation. The recrystallized sample is transparent and provides a higher light yield of 54,000 photons MeV–1, which is comparable to that of single-crystal Tl:CsI. The decay times are 400 ns (28%) and 1,350 ns (72%). This material can serve as a scintillator fiber with high sensitivity to γ- and X-rays, high light yield, and energy discrimination.

We report the gamma (γ)-ray radiation resistance of praseodymium (Pr3+)-doped aluminum lithium fluorophosphate scintillator glasses. For its assessment as a scintillator material for laser fusion experiments, a 20Al(PO3)3-80LiF-PrF3(Pr3+-doped APLF) glass was irradiated with γ-rays from a cobalt-60 (60Co) source resulting in an absorbed dose of 5.2 kGy. Although γ-ray-irradiation results in increased absorption due to phosphorus-oxygen hole centers (POHCs) and PO32−electron centers (PO3ECs), these radiation-induced defects do not modify the glass emission as both non-irradiated and γ-ray-irradiated glasses exhibit similar emission spectra and decay times under optical and X-ray excitation. The emission peaks observed also correspond to the different interconfigurational 4f5d → 4f2and intraconfigurational 4f2transitions of Pr3+ions which are neither oxidized nor reduced by irradiation. Our results show that Pr3+-doped APLF glass still maintains its characteristic fast decay time and that γ-ray irradiation does not affect the glass scintillation mechanisms.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease in East Asia. It is thought that the SFTS virus (SFTSV) circulates between ticks and animals in nature and that the virus is transmitted to humans by tick bites. SFTS is endemic to Nagasaki in western Japan; however, epidemiological information regarding SFTSV in Nagasaki is not known. In this study, we performed SFTSV IgG ELISAs and neutralization antibody assays for a seroepidemiological survey using samples from wild boars captured in six areas of Nagasaki. SFTSV seropositive animals were found in three areas. Our findings provide epidemiological information on the distribution of SFTSV in Nagasaki.

Japanese encephalitis (JE) is a mosquito-borne infectious disease caused by Japanese encephalitis virus (JEV). About 1–10 cases with severe central nervous system symptoms have been constantly reported every year in Japan. To clarify the mechanism of maintenance of JEV, the present study surveyed pigs for serological evidence of JEV infection and isolated JEV strains from pigs and mosquitoes in Isahaya City (Isahaya) and Goto City (Goto) in the islets of Goto in Nagasaki Prefecture from 2008 to 2014. The serological survey of pigs showed the increase of IgM sero-positivity against JEV in July or August, and it was maintained until October or November in both Isahaya and Goto every year. There were 47 JEV strains isolated in Nagasaki from 2001 to 2014 including the isolates in this study, and they belonged to genotype 1. Thirty four of the isolated strains were from pigs in Isahaya and were classified under six subclusters (1-A-1, 1-A-2, 1-A-3, 1-A-4, 1-A-5, and 1-A-9). Thirteen strains were isolated from pigs and mosquitoes in Goto and were classified into three subclusters (1-A-5 (2008); 1-A-1 (2009); and 1-A-2). In the subcluster 1-A-2, three different monophyletic subgroups, 1-A-2-2 (2010), 1-A-2-3 (2011), and 1-A-2-1 (2013, 2014), appeared in Goto. These data strongly suggested that JEV appearance in Goto seems to depend on the frequent introduction of JEV from outside of the island and this pattern is different from what has been observed in subtropical islands in the East China Sea such as Okinawa and Taiwan, where the same populations of JEV (1-A-7 (1998–2008) in Okinawa; genotype 3 (until 2012) in Taiwan) have been maintained for a long period.

ABSTRACTAn improved light-weight Compton camera exhibiting low power consumption was developed to be mountable on an unmanned helicopter to detect cesium radiation hot spots and confirm the decontamination effect of cesium-affected areas. An increase in the Ce:Gd3(Al,Ga)5O12scintillator array from 4 × 4 to 8 × 8 and expansion of the interlayer distance enhanced the detection efficiency and angular resolution, respectively. Measurements were performed over the Ukedo riverbed in Namie, Fukushima Prefecture (Japan). The helicopter's flight path and speed were pre-programmed to lines interspaced by 5 and 10 m intervals and 1 m/s, respectively, facilitating measurements over areas of 65 × 60 m2and 65 × 180 m2at a height of 10 m for approximately 20 and 30 min, respectively. Results provided accurate ambient dose equivalent rate maps at a height of 1 m with an angular resolution corresponding to a position resolution of approximately 10 m from a height of 10 m. Hovering flights were executed over hot-spot areas for 10–20 min at a height of 5–20 m. Gamma-ray images of these hot spots were obtained using a reconstruction software. Comparison between position-shifted measurement results showed that the angular resolution coincided with that evaluated in the laboratory (approximately 10°).

HfO2/α-Al2O3eutectics were grown by the micro-pulling down (μ-PD) method at the composition of 63.2 mol.% α-Al2O3, 35.512 mol.% HfO2, 0.92 mol.% Eu2O3and 0.368 mol.% Y2O3. Rod phases with around 3–4 μm diameter were observed on the transverse cross-section. The phase-separated scintillator fibers (PSSFs) structure with fibers of around 3–4 μm diameter and 10–20 μm length was observed. The electron back scattering patterns indicated crystal orientation of [101] for monoclinic HfO2rod phase and [0001] for α-Al2O3matrix in the transverse cross-section. Eu3+4f-4f emission was observed at 550–750 nm.

Due to the accident of Fukushima Daiichi Nuclear Power Plant, some areas were contaminated by released radioisotopes (mainly 137Cs and 134Cs). Effective decontamination is demanded to encourage evacuated people to return. This paper proposes a new survey system using an unmanned helicopter equipped with a Compton camera for localizing radionuclides. As a prototype, 32 Ce:Gd3(Al,Ga)5O12(GAGG) crystals were coupled to 16 silicon photomultipliers and 16 avalanched photodiodes as the scatterer and absorber, respectively. A new Dynamic Time-over-Threshold (dToT) method was applied to convert CR-RC shaping signals to digital signals for multi-channel spectra and coincidence acquisition. The system was designed to work in two modes: one is Compton-camera mode (CCM) which obtains the radiation distribution maps through Compton imaging using hovering flights, while the other one is Gamma-camera mode (GCM) which maps the radiation distribution via measured coincidence events using programmed flights. For point source in CCM, an intrinsic efficiency of 1.68% with a combined standard uncertainty of 0.04% and an angular resolution of about 14° (FWHM, full width at half maximum) was achieved. In GCM, a spatial resolution of about 11 cm (FWHM) was obtained when detecting area is 11.2 cm away from the detector, while it was about 28 cm (FWHM) in single detector mode (SDM). Promising results were obtained in field in Fukushima.

The optical and scintillation properties of Ce3+-doped YGd2(Al,Ga)5O12 single crystal scintillators were investigated. The Ce3+ 5d-4f emission was blue-shifted with increasing Ga content due to the decrease of the crystal field strength. Temperature dependence of the photoluminescence decay times was measured and the thermal activation energy for the luminescence quenching was calculated. Light yield (LY) and its dependence on an integration time were measured under γ-ray excitation. The fast component content in the scintillation response increases with increasing Ga content. The YGd2Al2Ga3O12:Ce sample showed a high LY of 38,000 photons/MeV. The decrease of LY value observed for a YGd2Al1Ga4O12:Ce sample is mainly due to the thermal ionization of the 5d1 excited state of the Ce3+ emission center to the conduction band.

(Ce0.002Y0.998−xLux)AlO3(x= 0.000, 0.010, 0.100, 0.200) single crystals were grown and characterized to clarify the effects of Lu substitution in Ce:YAlO3on its crystal structure, optical properties and thermal stability of Ce3+luminescence. The lattice constants of (Ce0.002Y0.798Lu0.200)AlO3were comparable to those of Ce:YAlO3, so the crystal structure was not significantly influenced by Lu substitution. Concerning the optical characterization, the absorption and emission spectra were almost the same regardless the amount of Lu substitution. This result is consistent with the assumption that the crystal field is not influenced by Lu substitution. The temperature dependences of the photoluminescence decay time showed that the quenching temperature (T50%) tends to increase with the increasing Lu concentration. We conclude that the leading quenching mechanism is the thermally activated ionization which is suppressed by the Lu substitution in Ce:YAlO3.

The influence of the reflected waves at the bonding boundary on the resonance waveform and temperature characteristics was investigated using a-quartz (QZ). The double-layered resonator specimen was fabricated using 129.55°Y- and 0°Y-cut QZ substrates with the thickness ratio x= 0.520. The temperature characteristic of the 1st and 2nd resonance modes at the range from 100 °C to 300 °C was deviated from the calculated values estimated by the equations considering thickness ratio and electric flux density ratio proposed in the previous work. Considering the phase matching conditions, it was clarified that the reflected waves at the bonding boundary are in phase in the lower acoustic impedance substrate and out of phase in the other substrate for the 1st mode, so the temperature characteristics are mainly dominated by that of the lower acoustic impedance substrate. In contrast, these relationships are reversed for the 2nd mode.

The compositional dependences of luminescence properties and light yield were studied in Ce3+ -doped Y1Gd2Al5-xGaxO12 (x = 2, 3, 4) single crystal scintillators. The Gd3+→ Ce3+ energy transfer was evidenced by photoluminescence excitation spectra of Ce3+ emission. With increasing Ga content in the garnet host, the Ce3+ luminescence from the lowest 5d level (5d1) was blue-shifted due to the decrease in the crystal field splitting of the 5d levels. High light yield (LY) value of ~36,000 ph/MeV was obtained for a Y1Gd2Al2Ga3O12:Ce sample under excitation with 662 keV γ-rays. The decrease of LY value was also observed with higher Ga content due to the thermal ionization from the 5d1 level to the conduction band.

We study Ce3+luminescence and scintillation characteristics in novel, high performing hosts among the oxide single crystal scintillators, the La-admixed Gd2Si2O7. Obtained characteristics are systematically compared with the earlier studied Lu2Si2O7host. We determine the barrier height of the thermal ionization of the Ce3+excited center, we address the effect of La-admixture on the physical characteristics, and we construct an energy level diagram of the material system. High scintillation efficiency, low afterglow, and the onset of Ce3+excited state ionization appearing well above room temperature indicate a large potential of La-admixed Gd2Si2O7in a variety of scintillating material applications.

Abstract

In this study, Eu:6LiCl/BaCl2with a high Li concentration was developed as a novel thermal neutron scintillator. Eu ions were doped as activators for the BaCl2phase, and Eu:6LiCl/BaCl2eutectics were grown via the vertical Bridgman–Stockbarger method in quartz ampoules (inner diameter = 4 mm). The Eu:6LiCl/BaCl2eutectic exhibited a lamellar eutectic structure and optical transparency. The 400 nm emission due to the Eu2+4f–5d transition was observed in the BaCl2phase by a cathode luminescence measurement. The light yield under neutrons was estimated to be over 20 200 photons MeV-1. A PSD study was also performed using gamma and alpha-rays. The Eu:6LiCl/BaCl2eutectic scintillator showed good potential for PSD.

A 6LiBr/CeBr3eutectic thermal-neutron scintillator, with a high 6Li concentration, was developed using the vertical Bridgman method. The grown eutectic contained an 6Li molar ratio of 35%, which is higher than those of the commercial neutron scintillators such as Ce:LiCaAlF6 and Ce:Cs2LiYCl6. Furthermore, it showed optical transparency and a lamellar eutectic structure elongating along the growth direction. The synthesized eutectic showed emission peaks at 360 and 380 nm, originating from the Ce3+5d-4f transition in the CeBr3scintillation phase. The scintillation performance of 6LiBr/CeBr3was evaluated under X-ray, ?-ray, and neutron irradiation to corroborate its neutron detection potential.

In this study, a large-size eutectic scintillator of Tb-doped BaCl2/NaCl/KCl was grown using the Czochralski (Cz) and halide vertical Bridgman methods (H-VB). The suitability of these two growth methods for growing the eutectic was compared. Finally, 1 inch diameter eutectic bulks were obtained using the H-VB method. The Tb3+-derived strongest intensity peak at approximately 550 nm was observed by X-ray irradiation. An approximately 3 × 3 mm transparent eutectic wafer was cut and polished from the grown eutectic bulk. An imaging test using a-ray was performed using the grown eutectic, a fiber optic plate, and an electron-multiplying CCD camera. The resolution performance for radiation-imaging applications was evaluated.

We demonstrated continuous-wave lasing of an AlGaN-based ultraviolet laser diode, fabricated on a single-crystal AlN substrate when operating at 5 °C. The threshold current density and device series resistance were reduced by improvements to the epitaxial structure and electrode arrangement. A peak wavelength of 274.8 nm was observed for lasing at a drive current over 110 mA, which corresponded to a threshold current density of 3.7 kA cm−2. The operating voltage at the threshold current was as low as 9.6 V.

ABSTRACTSevere fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with a high case fatality risk and is caused by the SFTS virus (SFTSV). A retrospective study conducted after the first identification of an SFTS patient in Japan revealed that SFTS is endemic to the region, and the virus exists indigenously in Japan. Since the nucleotide sequence of Japanese SFTSV strains contains considerable differences compared with that of Chinese strains, there is an urgent need to establish a sensitive and specific method capable of detecting the Chinese and Japanese strains of SFTSV. A conventional one-step reverse transcription-PCR (RT-PCR) (cvPCR) method and a quantitative one-step RT-PCR (qPCR) method were developed to detect the SFTSV genome. Both cvPCR and qPCR detected a Chinese SFTSV strain. Forty-one of 108 Japanese patients suspected of having SFTS showed a positive reaction by cvPCR. The results from the samples of 108 Japanese patients determined by the qPCR method were in almost complete agreement with those determined by cvPCR. The analyses of the viral copy number level in the patient blood samples at the acute phase determined by qPCR in association with the patient outcome confirmed that the SFTSV RNA load in the blood of the nonsurviving patients was significantly higher than that of the surviving patients. Therefore, the cvPCR and qPCR methods developed in this study can provide a powerful means for diagnosing SFTS. In addition, the detection of the SFTSV genome level by qPCR in the blood of the patients at the acute phase may serve as an indicator to predict the outcome of SFTS.

Ce and Ca co-doped LiGdF4-LiF eutectics were grown and their directionally solidified eutectic (DSE) system has been investigated. In these eutectics, apart from the expected 305 nm emission of the regular Ce3+, 310 nm emission of the Gd3+ and Ce3+-perturbed emission around 320-380 nm was observed. Ce3+-perturbed emission at 340 nm shows the intrinsic decay time of about 27 ns. In photoluminescence mechanism the observed decay time shortening of the regular Ce3+ and Gd3+ centers point to the energy transfer in the sequence the regular Ce3+→ (Gd3+)n→ the perturbed Ce3+ sites.

Carbon-doped Al2O3 is used as a material for dosimeter using thermoluminescence (TL) technique or optically stimulated luminescence (OSL) technique, and the emission bands are originated from defect emission. We have an original crystal growth named micro-pulling down (μ-PD) method which had higher temperature graduation during the crystal growth. Thus, crystal defect is easy to be formed without some dopant using the μ-PD method. We grew pure Al2O3 samples with different heating condition, and different peaks in TL spectra were obtained among the pure Al2O3.

We evaluated optical and scintillation properties of a Cr 0.5%:Y3Ga5O12 (YGG) and Cr 0.5%:Y3Al5O12 (YAG) crystals grown by the micro-pulling down method for infrared emission scintillators. In the photoluminescence and X-ray induced radioluminescence measurements, the emissions peaks of Cr:YGG were located in the longer wavelength than those of Cr:YAG. Radioluminescene spectrum of Cr:YGG had a broad peak at 716 nm related to Cr3+ 2E→4A2 and 4T→4A2 transitions.

Single crystals of a new quaternary compound, ErRh2B2C, were obtained by the flux growth method using molten copper as a flux. The extracted crystals show golden-coloured luster and a maximum size of approximately 1 × 1 × 0.02 mm3. This compound has tetragonal symmetry and appeared to be a derivative of the ThCr2Si2-type; the lattice parameters are a = 0.36848(2) nm and c = 1.05520(3) nm. The electrical resistivity parallel to the a-b plane of the crystal decreases with decreasing temperature. The residual resistance ratio ρ(273 K)/ρ(1.5 K) is 1.38. No superconductivity was observed down to 1.5 K. The search for similar types of new compounds was performed using the arc-melting synthetic method. The new quaternary RRh2B2C compounds are obtained for R = La – Er (except Eu) and Y. The phase stability of RRh2B2C was discussed.

Ca3NbGa3Si2O14 (CNGS) Is One of the Langasite-Type Crystals and it Is Known as a Piezoelectric Material. We Have Successfully Grown the Shaped CNGS Crystal Using Micro-Pulling-down (μ-PD) Method with Shape Control. However, the Impurity Phases such as Ca-Nb-O Related Compounds Were Detected in the Grown Crystals. The Creation of the Impurity Phases Is Related to Difference in Stoichiometric and Congruent Compositions. Therefore, the Detailed Investigation of Phase Diagram on CNGS Was Carried Out to Prevent the Impurity Phases Creation. It Follows from the TG-DTA Measurements that the Melting Point Systematically Changed with the Ca/Ga Ratio in the Ca3-xNbGa3+xSi2O14±δ Cmpositions. The CNGS Phase with Ca/Ga = 1.02 Indicated the Maximum Melting Point which Suggests that the Stoichiometric Composition of CNGS Is Different in the Congruent Composition. Furthermore, in the DTA Measurements the Peaks of Impurity Phases Were Detected around 1550 °C for the CNGS Sample with Ca/Ga = 1.02.

Ce and Mg Co-Doped LiCaAlF6 (LiCAF) Single Crystals Were Grown by Micro-Pulling-down (μ-PD) Method and the Optical and Scintillation Properties of Obtained Crystals Were Measured. The Grown Crystals Were Crack-Free and Had 30-50 mm in Length and 2 Mm in Diameter. Absorption Coefficients Were Proportional to the Ce Nominal Concentrations. the Radioluminescence Spectra under 5.5 Mev Alpha-Ray Irradiation Showed Emission Peak at 290 and 310 nm due to Ce3+ 5d-4f Transitions, and Were Agreement with those of Ce Single-Doped LiCaF. The Highest Light Yield under 5.5 Mev Alpha-Ray Irradiation of Ce 4% and Mg 2% Co-Doped LiCaF Was Found to Be 0.6 Times than that of Lithium Glass Scintillator GS-20. Comparing the Light Yield of Licaf Samples with the Fixed Ce Nominal Concentration and Different Mg Co-Doped Concentrations, the Light Yield Increased with an Increase of Mg Nominal Concentration. the Alpha-Ray Excited Decay Times Were Constantly 45-50 ns.

Single Crystals of Eu-Doped Calcium Orthoborate Have Been Grown by Micro-Pulling (μ-PD) Technique with Radio Frequency Heating System, and its Transmittance, Photoluminescence and Radiation Responses Were Investigated. In Transmittance Spectra, Eu-Doped Crystal Showed Broad Absorption Band around 200-450 nm, which Is due to the Complex of Charge Transfer (CT) Transition and 4f-4f Transition of Eu3+. Intense Eu2+ 5f-4f and Eu3+ 4f-4f Emission Peaks Were Observed when Excited to 265 nm and 385 nm, and the Calculated Decay Times Were 230 ns and 1.5 ms, Respectively. 241Am 5.5 Mev α-Ray Excited Radioluminescence Spectra Indicated both Eu2+ 5f-4f and EuSuperscript text3+ 4f-4f Emission Peaks.