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β-Ga2O3 is a well-known semiconductor material for power devices and other applications. Recently, β-Ga2O3 has also been reported as a scintillator material with a light yield of approximately 8400 ph./MeV, scintillation decay time of

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 ...

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.

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−1 for water and 0.5 dB mm−1 for 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.

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−1 under 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.

GdTaO4 and (Gd1-xTbx)TaO4 (x = 0, 0.001, 0.02, 0.04, 0.10, and 0.16) single crystals were grown by the micro-pulling down method. The crystallographic system of the grown crystals was identified to be monoclinic (I2/a), which is the stable low-temperature phase of GdTaO4. In the photoluminescence (PL) spectra, intense emission was observed at 549 nm (5D3→7F4 transition of Tb3+) for every Tb doped GdTaO4. In the excitation spectra for the 549 nm emission, several excitation paths to the Tb3+ were attributed: 4f-4f transitions of Gd3+, 4f8-4f75d transitions of Tb3+ and charge transfer of TaO43− group. Radiolumincece spectra under X-ray irradiation were taken, and the highest emission peak was observed at 544 nm, which was ascribed to the 5D4→7F5 transition of Tb3+. The Tb 2% doped GdTaO4 showed the highest emission intensity at the 544 nm, and as increasing dopant concentration, the intensity decreased due to the cross-relaxation of Tb3+.

Ce-doped LaBr3/AEBr2 (AE = Mg, Ca, Sr, Ba) eutectics were grown using the Bridgman&ndash, 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.

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, Lu0.388Hf0.612O1.806, and Lu0.18Hf0.82O1.91, with melting points of 2460, 2900, and 2840 &deg, 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 (&mu, PD) method. The Yb charge transfer state (CTS) emission was observed at 350 nm in the Yb1%-doped Lu2O3 and Lu0.18Hf0.82O1.91. In the case of the &mu, 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 (Gd, La)2Si2O7 (Ce:La-GPS) scintillator was found to have a good light output of around 40 000 photons/MeV, while some other parameters have not been determined so far. In order to clarify the cause for such a high light yield, some physical parameters have been estimated in this paper. The bandgap energy of Ce:La-GPS was evaluated to be over 7.13 ± 0.03 eV for (Gd0.75, La0.25)2Si2O7. Although Ce:La-GPS had wider bandgap compared with the other oxide scintillators, its light output was larger than values for some other scintillators. Since quantum yield of Ce:La-GPS was as high as around 0.8, the product of transfer efficiency and electron–hole pair generation efficiency was estimated to be around 0.9, which was higher than for the other scintillators. Thus, Ce:La-GPS was suggested to have high the product of transfer efficiency and/or electron–hole pair generation efficiency.

Single crystals of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 were grown by the Czochralski method. Structure analysis of the single crystals by X-ray diffraction (XRD) revealed that (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 crystalize in monoclinic cells (space group P21/c), a = 5.3905(8) A, b = 8.5605(11) A, c = 13.957(2) A, β = 112.223(6)o, and a = 5.3921(7) A, b = 8.5688(10) A, c = 13.9172(14) A, β = 111.980(5)o, respectively. One of the two different rare-earth sites is preferentially occupied by La and Gd atoms or by La, Ce and Gd atoms, and the other is occupied by Gd atoms only. Peaks attributed to the 4f-4f transitions (8S7/2–6G7/2 and 8S7/2–6Ix) of Gd3+ and 4f-5d transitions of Ce3+ were observed in the absorption spectra of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 single crystals.

This paper addresses several aspects of the µ-PD growth technology as applied to submillimeter diameter sapphire tubes for UFD application. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. A compound crucible made possible the growth of single crystal sapphire tube as small as around 0.70–0.72 mm in outer diameter and 0.28–0.29 in inner diameter over 160 mm in length at growth rate of 2–4 mm/min along 〈0 0 1〉 direction. An Ir crucible with a die composed of an equivalent hole and Ir wire was heated by RF coil in N2 atmosphere. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. Grown crystal tube showed good XRC value of 30.2 arcsec.

The fabrication and thermal electromotive force characteristics of Ir/Ir-Rh thermocouples capable of repeated bending deformation are described. Ir and Ir-Rh wires with a diameter of 0.5 mm were fabricated using the alloy-micro-pulling-down method. Scanning electron microscopy and electron backscattering diffraction of the radial cross section of the grown wires were performed to investigate the microstructure and orientation of the crystal grains. At the start of growth, the microstructure was polycrystalline with diameters of several hundred micrometers, while at the 8-m growth point it was found to be monocrystalline. The observed single crystals of pure Ir and Ir-Rh alloy were oriented in the 〈1 1 3〉 and 〈1 1 2〉 directions, respectively, whereas the polycrystalline Ir-Rh samples showed preferential growth in the 〈1 0 0〉 direction. The thermal electromotive force of the fabricated Ir/Ir-Rh thermocouple was measured by the comparison technique and the fixed-point technique, and the thermoelectric power was estimated to be 5.9 μV/°C in the range from 600°C to 1100°C.

Ce-doped (Gd, La) 2 Si 2 O 7 scintillation crystals are expected to be used as gamma-ray detectors for high temperature measurement. To realize scintillators for high temperature environment, we investigated (Ce 0.01 Gd 0.59−x La 0.40 Y x ) 2 Si 2 O 7 (x = 0.00, 0.05, 0.10, 0.15) single crystals grown by the micro-pulling-down method. The results showed that a 5% Y-admixed Ce-doped (Gd, La) 2 Si 2 O 7 scintillator can yield higher light output when compared with Y-free Ce-doped (Gd, La) 2 Si 2 O 7 scintillator. The light outputs at 25°C and 175°C were determined to be ∼43,000 and ∼40,000 photons/MeV, respectively. Moreover, 1 inch size 5% Y-admixed Ce-doped (Gd, La) 2 Si 2 O 7 scintillator was grown by the Czochralski technique, and its light output at 175°C kept the value of around 95% of the value at 25°C.

A 6LiCl/6Li2SrCl4 eutectic scintillator with a high Li concentration was developed as a novel thermal neutron scintillator. Eu2+ served as an activator for the 6Li2SrCl4 phase, and Eu-doped 6LiCl/6Li2SrCl4 eutectics were grown via the Bridgman Stockbarger method in quartz ampoules (inner diameter = 4 mm). The Eu-doped 6LiCl/6Li2SrCl4 eutectics exhibited a lamellar-type eutectic structure and optical transparency, as well as 400 nm emission due to Eu2+ 5d-4f transition. The scintillation properties of the eutectics were evaluated under gamma- and alpha-ray irradiation to demonstrate its potential as a thermal neutron scintillator.

Iridium, ruthenium, and iridium-ruthenium alloy wires were fabricated by the dewetting micro-pulling-down method, a type of unidirectional solidification method. The length of the grown Ir-20Ru reached 47 m. Furthermore, their mechanical and thermoelectric properties were investigated. The as-grown Ir-17.9Ru wire exhibited a tensile strength of approximately 765 MPa and a nominal fracture elongation of 21% at room temperature. After work-hardening by three cycles of winding and rewinding for a bending radius of 10 mm and annealing at 2273 K for 3 h, the tensile strength and fracture elongation of the Ir-Ru wire were 1061 MPa and 25%, respectively. From the electromotive force (EMF) characteristics of platinum obtained by integrating the Seebeck coefficient, the EMF characteristics from room temperature to ~ 2000 K of iridium, ruthenium, and Ir-17.9Ru were investigated. The EMF characteristics for several thermocouples using iridium, ruthenium, or Ir-17.9Ru as one of the pairs were estimated from the combination of the obtained EMF characteristics. Ir/Ir-17.9Ru showed similar EMF characteristics to Ir-40Rh/Ir.

In this study, one-inch diameter Tl:CsI/CsCl/NaCl eutectic scintillators were grown by the Czochralski method at various pulling rates. Crystal growth conditions such as rotation, pulling rates, and crystal growth setup were analyzed. By examining the structure of the obtained eutectic, the growth orientation of the CsI phase as well as the optimum pulling speed and rotation speed were found. A transparent eutectic plate of about 3 × 5 mm was prepared from the grown sample, and scintillation properties such as light output and decay time after excitation by 662 keV gamma-rays were evaluated. The performance was compared with the Tl: CsI single crystal standard. Furthermore, a β-ray imaging test was carried out by combining the eutectic plate and an electron-multiplied charge coupling device camera, and the position resolution as an imaging device was evaluated.

The development of a real-time dose monitor system is one of the important issues in medical engineering to reduce medical accidents such as overdose or incorrect positioning of the treated human tissue during radiation therapy. One of the challenging solutions is to use an infrared scintillator, which is sufficiently bright so that the light can be detected outside the human tissue. In this study, a novel infrared scintillator, Cr-doped Gd 3 Ga 5 O 12 , was tested with pork meat as a phantom of human tissue to prove its feasibility for the dose monitor. The scintillation photons of Cr:Gd 3 Ga 5 O 12 were observed through even 50-mm thick pork meat. The emission peak originated from d-d emission of Cr 3+ . The emission intensity of Cr:Gd 3 Ga 5 O 12 was approximately 3.5 times larger than that of the conventional infrared scintillator Cr:α-Al 2 O 3 . Moreover, we succeeded in performing the infrared imaging for Cr:Gd 3 Ga 5 O 12 irradiated with alpha-rays using a complementary metal oxide semiconductor camera.

Ce-doped (Gd, La)2Si2O7 scintillators have fast decay time and keep high light output even at high temperature (∼150°C). To improve the scintillation properties such as light output and decay time, Ce-doped (Gd, La)2Si2O7 scintillators codoped with the divalent ions (e.g. Mg2+, Ca2+) have been studied. In this study, we focused on the other divalent ions (Sr2+ and Ba2+), and investigated their effect on the scintillation properties and temperature dependence of light output. The absorption due to Ce4+ was not observed for Sr or Ba codoping. The light outputs were degraded by Sr2+ or Ba2+ codoping, while the decay times at room temperature were not changed for the samples codoped with divalent ions. On the other hand, the temperature dependence of light output for Ba-codoped sample was improved, and the light output value at 175°C was 36,000 photons/MeV, which was 93% of that at 25°C.

Ce-doped Lu 2 Si 2 O 7 scintillator contains radioactive isotope 176 Lu which causes an unwanted intrinsic background signal. The development of scintillators with reduced Lu concentration were required in some applications. In this study, we developed the Gd admixed lutetium pyrosilicate, where the average ion radius at the rare earth site was similar to the Tm 3+ ion radius, for which the RE 2 Si 2 O 7 (RE=Tm, Yb, Lu) crystal structure is stable from room temperature to melting point. We have grown (Ce x Lu 1−x−y Gd y ) 2 Si 2 O 7 (x=0.01, y=0.00, 0.05, 0.10) single crystals. Their crystal systems were monoclinic with a space group C 2/ m . The absorption spectra revealed the energy transitions in Ce and Gd ions might be occurred. The light output was degraded and decay time was accelerated comparing the Gd 5% admixed sample with the Gd 10% one.

In this study, Eu and Ce doped LiSrI3 single crystals were explored and the scintillation performance was reported at the first time. Eu and Ce doped LiSrI3 single crystals were grown by the Bridgman–Stockbarger method in a quartz ampoule with 3 mm inner diameter. Growth rate was 0.06 mm/min. Circular samples with 1 mm thickness were obtained from the grown crystal. The grown Eu doped LiSrI3 crystal demonstrated Eu2+ 4f–5d emission peak at 420 nm under alpha-ray excitation. In the case of Ce doped one, double emission peaks at 360 and 400 nm were observed. The light yield of the Eu doped LiSrI3 was around 35,000 photon/MeV for 662 keV gamma-ray and 24,000 photon/5.5 MeV for alpha-ray. Energy resolution of the Eu doped LiSrI3 was 5.2%@662 keV. Scintillation decay time of the grown Ce and Eu doped LiSrI3 under 662 keV gamma-ray was 23.8 ns (50%) 212 ns (50%) and 545 ns 100%, respectively.

(Ce0.01 Gd0.59 La0.40)2Si2O7 single crystal (La40% sample) was grown by the micro-pulling-down method to study its scintillation properties and their temperature dependence. In addition, we investigated the relation between these properties and La concentration comparing the crystal with (Ce0.01 Gd0.90 La0.09)2Si2O7 (La9% sample). As results, the light output of the La40% sample at 25°C was similar to that of the La9% sample. On the other hand, the decay time of the La40% sample was slower than that of the La9% sample at 25°C. The light output of La40% sample had a small decrease rate at high temperature when compared with that of La9% sample.

The luminescence and scintillation properties of Gd1.53La0.47Si2O7:Ce (GPSLa23.5%:Ce) scintillators were investigated and compared to those of Lu1.9Y0.1SiO5:Ce (LYSO:Ce) scintillators. At 662 keV γ-rays, the light yield of 33,500±3300 ph/MeV obtained for GPSLa23.5%:Ce is higher than that of 28,100±2800 ph/MeV obtained for LYSO:Ce. The energy resolution of 4.8±0.2% obtained for GPSLa23.5%:Ce is much better than that of 8.2±0.3% obtained for LYSO:Ce due to its better intrinsic resolution and proportionality of light yield. The light yield and energy resolution for α- rays, as well as a light yield ratio under excitation with α - and γ - rays (α/γ ratio) were also determined. The intrinsic light yield and light loss coefficient under excitation with 662 keV γ-rays were evaluated. The total attenuation coefficient at 60 keV and 662 keV γ - rays was also determined and compared with the theoretical one calculated using the WinXCom program.

Growth of 2-in. diameter Ce-doped (La , Gd) 2 Si 2 O 7 (La-GPS) scintillating crystals by Czochralski method using Ir crucible is reported. The composition of the host material was approximately equal to La 0.5 Gd 1.5 Si 2 O 7 and the concentration of the Ce 3+ -activator was either 0.5 or 1.5 at.% with respect to the total content of the rare-earths forming the host crystal matrix. Effects of the hot zone construction including inductive coil position, presence/absence of the after-heater, rotation rate and other growth parameters on the crystal quality are discussed in some details. The crystals produced in optimized conditions were colorless, transparent, uniform in their shape, crack- and inclusions-free, and demonstrated smooth glass-like surface. The length of the crystals’ cylindrically-shaped body parts exceed 100 mm. The growth results were well reproducible. The main disadvantage of the growth process is associated with short lifetime of the Ir crucible and its deformation caused by thermal expansion of the pre-solidified melt at each heating stage.

The scintillation timing characteristics of (La,Gd)2Si2O7:Ce (GPSLa23.5%:Ce) single crystal were studied and compared with Gd2SiO5:Ce (GSO:Ce) single crystal. The photoelectron yield, scintillation decay times and coincidence time resolution were measured. At 511 keV γ-rays, the photoelectron yield of 10,770 ± 500 phe MeV−1 and energy resolution of 5.4 ± 0.2% obtained for GPSLa23.5%:Ce are much better than those of 3350 ± 160 phe MeV−1 and 7.8 ± 0.3% obtained for GSO:Ce. The scintillation decay time profile was measured by the time-correlated single photon counting technique using a fast-slow coincidence setup. In both materials the comparable rise times of several nanoseconds are present. The fast component decay time of 56 ns with relative intensity of 49% obtained for GPSLa23.5%:Ce is inferior to that of 32 ns(88%) obtained for GSO:Ce. Consequently, the coincidence time resolution of GPSLa23.5%:Ce is slightly worse than that of GSO:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.

(CexYb1−x)2Si2O7 (x = 0.00, 0.01) single crystals were grown by the micro-pulling-down method to test the possibility of its application as infra-red scintillator for medical imaging. Powder X-ray diffraction analysis indicated that the crystals were single-phase materials. The radioluminescence spectra of the crystals demonstrated presence of two near infra-red emission peaks (at 1010 and 1030 nm). The emission peaks at 420 and 580 nm ascribed to defects were also observed in the crystals. The human body has maximum transmission in wavelength range from 650 to 1200 nm. Therefore, Yb2Si2O7 is expected to be used as efficient infra-red scintillator for medical applications.

(Gd 0.75 ,Ce 0.015 ,La 0.235 ) 2 Si 2 O 7 (Ce:La-GPS) single crystals co-doped with 0, 100, 200, 500 and 1000 ppm Zr were grown by the Czochralski process, and their scintillation properties were investigated. We investigated the co-doping effect of a stable tetravalent ion in Ce:La-GPS for the first time. The scintillation decay times in the faster component were shortened with increasing the Zr concentration. While the non-co-doped sample showed ∼63 ns day time, the Zr 100, 200, 500 and 1000 ppm co-doped samples showed ∼61, ∼59, ∼57, ∼54 ns, respectively. Additionally, light output, photon nonproportional response (PNR) and other optical properties were investigated.

1300 or 1400 °C pre–sintered Al/Ce/Mg:SrHfO 3 and Al/Ce:SrHfO 3 ceramics were prepared by the Spark Plasma Sintering (SPS) in order to search for a new scintillation material with a high–effective atomic number(Z eff ) and good light output. The SrHfO 3 has a high Z eff of 60, and high gamma–ray detection efficiency is expected. Meanwhile it has a high melting point of over 2500 °C, and single crystal is hard to be grown. On the other hand, high melting materials can be prepared as ceramics, and the SPS method is a simple process to fabricate the ceramics within a few hours. Thus, we prepared the samples using the SPS method, and their optical and scintillation properties were investigated. We found that Al/Ce/Mg:SrHfO 3 and Al/Ce:SrHfO 3 ceramics had an emission wavelength at around 400 nm originating from 5d–4f transition of Ce 3+ . Moreover, Al/Ce/Mg:SrHfO 3 pre-sintered at a temperature of 1400 °C had a light output of approximately 5,000 ph/MeV. In this paper, the light output of Mg-co-doped samples was improved compared with the Mg-free ones. The light output also depends on the pre-sintering temperature.