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 <1 μs, and density of 6.44 g/cm³. In this study, 45 cm diameter β-Ga₂O₃ single crystals were prepared via oxide crystal growth using the cold crucible (OCCC) method under various oxygen partial pressures. In the OCCC method, as in the cold crucible method, a high frequency is applied directly to the oxide materials, which are heated and melted, and the melt is held by the outermost solid material itself that is cooled by water using a copper hearth. In the OCCC method, crystal growth is performed while rotating the seed crystal, as in the Czochralski method, to increase the crystal diameter. The optical properties and radiation responses of the crystals grown under various oxygen partial pressures were evaluated.

Scintillators are key components in high-energy x-ray detectors for x-ray computed tomography, which are applied in medical diagnosis, nondestructive testing, and security inspection. Scintillators in x-ray imaging are required to have both high spatial resolution and sensitivity; however, a trade-off between spatial resolution and sensitivity exists. To improve the sensitivity of a scintillator, its thickness must be increased; however, spatial resolution deteriorates with increasing thickness. Here, we developed a well-aligned Tb-doped GdAlO₃-αAl₂O₃ phase-separated scintillator fiber (PSSF) with a diameter of 1.25-μm by a micro-pulling-down method. The luminescence, scintillation, and imaging performances of a grown PSSF sample were evaluated. X-ray-induced radioluminescence measurements of the sample showed Tb³⁺ 4f–4f emissions in the wavelength range of 470–700 nm, and the maximum emission peak was at 550 nm. The contrast transfer function at 10 lp/mm was 82% for both 270 and 500 μm-thick PSSF samples. We calculated the luminescence index, which is the product of the scintillator’s light yield and sensitivity, of the samples and compared their values with commercially available conventional CsI:Tl columnar scintillators. The Tb-doped GdAlO₃-αAl₂O₃ PSSF exhibits higher contrast transfer function and luminescence index values at above 60 keV x-ray region compared with the tested conventional scintillators.

In this study, a novel thermal neutron scintillator of Tl:CsI/LiBr was developed. The eutectics were fabricated at the various growth rate and investigated their scintillation properties. As a material design guideline, Tl:CsI, which has an excellent α/γ ratio, was selected as the scintillator phase to realize high light yield at the energy of α-rays and tritons generated by the nuclear transmutation reaction with ⁶ Li, and LiBr, which has a refractive index close to that of CsI, was selected as the neutron capture phase. Radioluminescence 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 ²⁵² Cf 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 ⁶ Li concentration compared to conventional single crystal scintillators. Therefore, we have succeeded in developing a promising scintillator material.

To date, ³He gas has been commonly used to detect thermal neutrons because of their high chemical stability and low sensitivity to γ-rays, owing to their low density and large neutron capture cross-section. However, the depletion of ³He gas prompts the development of a new solid scintillator for thermal neutron detection to replace ³He gas detectors. Solid scintillators containing ⁶Li are commonly used to detect thermal neutrons. However, they are currently used in single crystals only, and their ⁶Li concentration is defined by their chemical composition. In this study, ⁶Li-containing eutectic scintillators were developed. CeCl₃ was selected as the scintillator phase because of its low density (3.9 g/cm³); high light yield (30,000 photons/MeV); and fast decay time with four components of 4.4 ns (6.6%), 23.2 ns (69.6%), 70 ns (7.5%) and >10 μs (16.3%), owing to the Ce³⁺ 5d-4f emission peak at approximately 360 nm. Crystals of the CeCl₃, LiCl and CaCl₂ ternary eutectic were fabricated by the vertical Bridgman technique. The grown eutectic crystals exhibited Ce³⁺ 5d-4f emission with a peak at 360 nm. The light yield was 18,000 photons/neutron, and the decay time was 10.5 ns (27.7%) and 40.1 ns (72.3%). Therefore, this work demonstrates optimization by combining a scintillator phase and Li-rich matrix phase for high Li content, fast timing, high light yield and low density.

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.