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The 3He gas is commonly used for the detection of thermal neutrons. However, with the depletion of 3He gas, there is a need to develop new solid scintillators for thermal neutron detection. Solid scintillators containing 6Li, which have large neutron capture cross-sections and a large amount of energy released by transmutation reactions, are commonly used as alternative candidates. However, only single-crystal scintillators are currently used, and their 6Li concentration is limited by their chemical composition. In this study, we designed, grew, and evaluated a new eutectic scintillator, Rb2CeCl5/LiCl, which can improve the 6Li concentration compared with single-crystal scintillators. Rb2CeCl5, which was selected as the scintillator phase, has excellent scintillator properties (light yield: 36,000 photons/MeV, decay time: mostly 24 ns, slightly 153 ns), and is less deliquescent than other halide scintillators. The crystal grown using the vertical Bridgman method exhibited a eutectic phase composed of Rb2CeCl5 and LiCl. The eutectic crystals exhibited Ce3+ 5d-4f emissions, with a peak between 360 and 370 nm. The Rb2CeCl5 phase was identified as the luminescent phase via cathodoluminescence mapping, and 16,000 photons/neutron of the light yield and 56.1 ns of the decay time were observed. This study indicates that the Rb2CeCl5/LiCl eutectic scintillator is a promising candidate for use in thermal neutron detectors. [ABSTRACT FROM AUTHOR]

In recent years, thermal neutron detection using scintillators has been used in a wide range of fields. Thus, the development of scintillators with a higher light yield, faster decay, and higher sensitivity for thermal neutrons is required. In this study, K2CeCl5/6LiCl and CeCl3/SrCl2/6LiCl were developed as novel eutectic scintillators for thermal neutron detection. LiCl was selected as the neutron capture phase and K2CeCl5 and CeCl3 were used as the scintillator phases. The eutectics of K2CeCl5/6LiCl and CeCl3/SrCl2/6LiCl were prepared using the Vertical Bridgman method and the phases were identified by scanning electron microscopy and powder X-ray diffraction measurements. The results of radioluminescence measurements under Ag source X-ray tube irradiation confirmed that the 5d-4f emission derived from Ce3+. The cathodoluminescence spectra and thermal neutron responses of the prepared eutectics were measured to evaluate their optical properties. [ABSTRACT FROM AUTHOR]

• Mg 2 Si/Si eutectics of 1 in. in diameter were solidified by the VB method at three pulling rates. • The Mg 2 Si/Si eutectics indicated a phase-separated eutectic structure of the Mg 2 Si and Si phases. • The eutectic morphology became finer with an increase in the pulling rate. • The thermal conductivity systematically decreased with an increase in the pulling rate. • The power factor was improved in the temperature ranges above 400 °C compared to the Mg 2 Si. • The ZT value reached 0.076 at 600 °C for the Mg 2 Si/Si solidified at a 103 pulling rate. Mg 2 Si/Si eutectics are grown from melt by the Vertical Bridgman method using a carbon crucible at three pulling rates. All the Mg 2 Si/Si eutectics are composed of Mg 2 Si and Si phases, and the eutectic structure becomes finer with an increase in the pulling rate. Increasing the pulling rate systematically decreases the thermal conductivities of the Mg 2 Si/Si eutectics, suggesting that a decrease in the thermal conductivity is attributed to an increase in phonon scattering at the boundaries between the two phases. The power factor and figure of merit of the Mg 2 Si/Si eutectics are larger than those of Mg 2 Si above 400 °C because of the increase in the Seebeck coefficient. The figure of merit, ZT , of the Mg 2 Si/Si eutectics solidified at a 103 mm/min pulling rate reached 0.076 at 600 °C. [ABSTRACT FROM AUTHOR]

• La-doped SrTiO 3 /TiO 2 eutectic crystals were grown by a micro-pulling-down method. • Grown crystals were composed of the TiO 2 rod phase in the SrTiO 3 matrix phase. • Diameter of TiO 2 rods systematically decreased as the growth rate was increased. • Grown crystal exhibited a lower thermal conductivity than the SrTiO 3 single crystal. • ZT s of crystals grown at 0.02 and 0.5 mm/min were 0.015 and 0.025, respectively. La-doped SrTiO 3 /TiO 2 (La:STO/TO) eutectic crystals were grown by a micro-pulling-down method at various growth rates to control the eutectic morphology and thermoelectric properties. The La:STO/TO eutectic crystals were composed of a TiO 2 (TO) rod phase in the SrTiO 3 (STO) matrix phase for all growth rates. The diameter of the TO rod phase systematically decreased as the growth rate was increased, according to the Jackson–Hunt model, and the diameter reached approximately 1 μm at a growth rate of 1 mm/min. The La:STO/TO eutectic crystal exhibited a lower thermal conductivity than the Nb:STO single crystal, owing to the decrease in the lattice thermal conductivity by phonon scattering at boundaries in the eutectic morphology. The figures of merit, ZT s, of the La:STO/TO eutectic crystals grown at 0.02 and 0.5 mm/min growth rates were 0.015 and 0.025, respectively. The faster growth rate led to an increased ZT, owing to the decrease in electrical resistivity. [ABSTRACT FROM AUTHOR]

• Phase diagram for the CsI-LiBr binary system established. • Vertical Bridgman method employed for crystal growth. • Homogeneous eutectic crystals obtained. • Light yield (thermal neutron irradiation) was 6.7 times higher than that of the LiCAF. • This helps development of eutectic scintillators with improved crystal structure. 3He gas detectors have been commonly used in applied technology related to thermal neutron detectors; however, owing to the depletion of 3He, applications using solid-state scintillators are expanding. In recent years, our group has reported a novel Tl:CsI/6LiBr eutectic scintillator for thermal neutron detection, which has excellent light yield and (n,γ) discrimination ability. In practical applications of eutectic scintillators, achieving eutectic production precisely at the eutectic point is crucial to ensure a high production yield and the development of a uniform eutectic structure. However, the phase diagram of the CsI-LiBr system has not yet been reported. In this study, the phase diagram obtained from calorimetry was investigated. Furthermore, eutectic fabrication was performed at the eutectic point, and the neutron response was evaluated. [ABSTRACT FROM AUTHOR]

• Ce doped LaCl 3 /AECl 2 (AE = Mg, Ca, Sr) eutectics were grown by BS method. • In case of AE = Mg, Ca, eutectic with PSSFs structures were observed. • The Ce:LaCl 3 /CaCl 2 eutectic showed Ce3+ 4f-5d emission at 345 nm. • The light output of Ce:LaCl 3 /CaCl 2 under 137Cs was 9000 photons/MeV. • The scintillation decay time under 137Cs was 26.8 ns (26%) and 282 ns (74%). Ce-doped LaCl 3 /AECl 2 (AE = Mg, Ca, Sr) system eutectics were explored. Ce-doped LaCl 3 / AECl 2 (AE = Mg, Ca, Sr) eutectics were grown using the Bridgman–Stockbarger method in quartz ampoules. In the case of AE = Mg, Ca, eutectics with submicron-diameter phase-separated scintillator fibers (PSSFs) structure were observed. In the case of AE = Sr sample, a solid solution of La 0.708 Sr 0.292 Cl 2.708 was observed. The plate sample from the grown eutectics has some transparency. The grown eutectic structure showed a mixture of rods and plates shape. This mixed structure was aligned with a length of around 100–400 μm. The Ce:LaCl 3 /CaCl 2 eutectic showed 345 nm emission ascribed to Ce3+ 4f-5d transition under X-ray excitation. The Ce:LaCl 3 /CaCl 2 sample resulted in the highest light output of 9,000 photon/MeV, which is comparable to the previously reported eutectic scintillator Ce:GdAlO 3 /α-Al 2 O 3 , 9500 photon/MeV. Scintillation decay time of the Ce:LaCl 3 /CaCl 2 sample under 662 keV gamma-ray excitation was 26.8 ns (26%) and 282 ns (74%). [ABSTRACT FROM AUTHOR]

In this study, Ce:6LiBr/LaBr 3 eutectic with a high Li concentration was developed as a novel thermal neutron scintillator. Ce served as an activator for the LaBr 3 phase, and Ce:6LiBr/LaBr 3 eutectics were grown via the vertical Bridgman method in quartz ampoules (inner diameter = 4 mm). In the eutectic, the 6LiBr phase worked as the neutron capture phase by the 6Li (n, a) 3H reaction, and Ce:LaBr 3 worked as the scintillator phase. The Ce:6LiBr/LaBr 3 eutectic exhibited a lamellar eutectic structure and optical transparency, as well as 350 and 380 nm emission due to Ce 3 + 5d-4f transition. The light yield under neutrons excitation was estimated to be 74000 photons/neutron. The scintillation decay time was 18.7 ns. • Optically semitransparent Ce-doped 6LiBr/LaBr 3 eutectic was grown. • The vertical Bridgman–Stockbarger (VB) method enables unidirectional solidification to grow the directionally solidified eutectic (DSE). • Ce 3 + emission peaks at 350 and 380 nm were observed in the LaBr 3 phase. • Scintillation decay time under 252Cf neutron excitation was 18.7 ns. • The light yield under 252Cf neutron excitation was around 74000 photon/neutron. [ABSTRACT FROM AUTHOR]

• A novel ternary Tb:BaCl 2 /NaCl/KCl eutectic scintillator is reported. • Directionally solidified eutectic was grown by the VB method. • Columnar BaCl 2 fibres with a length of 300 μm were obtained at a growth rate of 0.01 mm/min. • The expected Tb3+ emission was observed only in the BaCl 2 phase. • The decay times of the eutectic were 0.49 ms (7.5%) and 6.64 ms (92.5%) In this study, Tb:BaCl 2 and NaCl/KCl ternary eutectics were grown using quartz ampoules via the vertical Bridgman–Stockbarger method. Each crystal phase had a polygonal columnar shape with a length of 300 µm along the growth direction. The Tb:BaCl 2 scintillator phase grew in the columnar phase. The BaCl 2 scintillator phase is expected to make optical waveguides of the scintillation light. The expected Tb3+ emission peak was observed at approximately 360–630 nm under X-ray irradiation. This emission is mainly attributed to the Tb3+5D 4 →7F 6, 7F 6 , 7F 5 , 7F 4 , and 7F 3 transitions and BaCl 2 host emission transition. The photoluminescence decay times of the Tb:BaCl 2 /NaCl/KCl eutectics was 0.49 ms (7.5%) and 6.64 ms (92.5%). [ABSTRACT FROM AUTHOR]

• A novel ternary CsI/KI/KCl eutectic scintillator is reported. • Directionally solidified eutectic was grown using the Bridgman–Stockbarger method. • The expected Tl+ emission peak near 486 nm was observed in the CsI phase. • The decay time of the eutectic was 313 ns. • The light output of the eutectic was approximately 22,000 photons/MeV. In this study, Tl:CsI/KI/KCl eutectic scintillators were grown using the Bridgman–Stockbarger method by unidirectional solidification. The eutectic phases were uniformly distributed in the transverse direction and were slightly aligned along the growth direction. The Tl:CsI scintillator phase was grown as a matrix, which was then used for creating optical waveguides of the scintillation light. The expected Tl+ emission peak was observed at 486 nm under X-ray excitation and cathodoluminescence; this was attributed to the self-trapped exciton perturbed by TI+ in Tl:CsI. The decay time of the Tl:CsI/KI/KCl eutectic was 313 ns, and its light output was estimated to be 22,000 photons/MeV. [ABSTRACT FROM AUTHOR]