Αlpha-Ray Detection Properties of Spinel Single Crystals

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A scintillator is one of the phosphors for radiation detection. Typical application fields of scintillators are medical, security, and environmental dosimetry. In nuclear facilities, there are high doses of α-ray, and monitoring of α-ray is necessary. Up to now, Ag-doped ZnS is used for α-ray detection. Although Ag-doped ZnS has high light yield, the detection efficiency is limited because the material form is opaque polycrystal. Therefore, a novel scintillator with high transparency is required for α-ray detection. Spinel materials are one of the candidates for radiation detection because of their high radiation resistant. According to the previous study, scintillation properties of MgGa2O4 and ZnGa2O4 have been studied under γ-ray irradiation. On the other hand, these materials seem to be suitable for α-ray detection rather than γ-ray detection because of the low effective atomic number. In addition, other spinel materials also worth studying. In this study, we synthesized MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals and evaluated the optical and scintillation properties.The starting powders were MgO, ZnO, Al2O3, Ga2O3. The powders were mixed into homogeneously and shaped into cylindrical rods by packing into balloon and applying hydrostatic pressure. Then, the rods were sintered 1400°C for 8 h in air to obtain ceramics precursor. Single crystalline samples were synthesized by the floating zone method using the ceramics precursor. For measurements, the synthesized crystals were processed to approximately 5 mm in diameter and 1 mm in thickness by cut and polishing.The transparent and single-phase of the MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals were successfully obtained by the floating zone method. According to the total transmission spectra, the total transmittances of the crystals were 70−80% in visible region. In the X-ray-induced scintillation spectra, MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals showed a luminescence peak around 380, 400, 300, and 350 nm, respectively. The luminescence origin of each crystal was considered to be due to oxygen vacancies of the host materials. Figure 1 shows the pulse height spectra of the spinel crystals under 241Am α-ray irradiation. The spectra of a commercial Bi4Ge3O12 (BGO, 8000 ph/MeV) single crystal under 137Cs γ-ray irradiation is also shown as a reference. As shown in Figure 1, all the crystals showed a clear full energy peak. From the comparison with the peak position of BGO, the light yields of the MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals were 200, 4300, 700, 5700 ph/5.5MeV-α, respectively. The details will be discussed in the conference. Figure 1