Kenji Shirasaki

Scintillation Properties of

Nd³⁺-doped Lu₂O₃ (Nd: Lu₂O₃) is a candidate for an infrared scintillator because (i) Lu₂O₃ has a high density of 9.5 g/cm³ and a high atomic number of 67 and (ii) Nd³⁺-doped materials emit in the infrared range and the emission lines from Nd³⁺ can be used in medical applications since human body has a transparency window between 600 and 1,100 nm. However, it is extremely difficult to fabricate Lu₂O₃ single crystals using conventional crystal growth methods because of the high melting point (2,510 ^° C). Using solid-state reactions, it is much easier to fabricate Lu₂O₃ into a ceramic structure. Therefore, Nd: Lu₂O₃ transparent ceramics were fabricated using a spark plasma sintering method. This technique is comparatively simple and consumes less time than other methods such as vacuum hot pressing. The scintillation properties and transmittance spectra of the as-produced ceramics were studied in both the visible and infrared regions. Radioluminescence spectra were measured in the range 800-1,200 nm. Nd³⁺ emission lines were observed in the transparency window of human body. Thus, these ceramic materials could be a candidate for medical imaging applications.

{\rm Nd}^{3+}

Energy efficiency of uranium redox-flow battery was evaluated on the basis of overvoltage evaluated by Butler–Volmer equation using standard rate constants of U(III)/U(IV) and U(V)/U(VI) in aprotic solvents. Though uranium–acetylacetonate complexes exhibit complicated electrode reactions and requires further improvements, a redox diagram prepared on the basis of determined E 1/2 values can be compared with that of neptunium which is suitable for the battery. The energy efficiency of the uranium battery was evaluated at various current densities on the basis of Butler–Volmer equation and the results were compared with those of neptunium and vanadium redox-flow batteries. At the current density of 70 mA cm -2 , the energy efficiency evaluated was 98.0%, which is 15% higher than that of the vanadium battery. The uranium battery has an excellent charge and discharge performance in comparison with the existing vanadium battery.

-Doped

In order to develop an alternative preparation method of uranium(III) precursors soluble in aprotic organic solvent used for the preparation of uranium(III) compounds, U(IV) triflate, U(OTf) 4 , in tetrahydrofuran (THF) was reduced to produce uranium(III) triflate. U(OTf) 4 in THF was completely reduced by large excess of zinc within 25 minutes. Energies and molar coefficients of the absorption bands of U(III) triflate are close to those of U(III) in 1M HCl aqueous solution especially in the range of (9 -14) ×10 3 cm -1 . U(III) triflate solution maintains its oxidation state in THF is when it is contacted with zinc amalgam for more than a week.