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[en] Absorption, emission and thermostimulated luminescence (TSL) of as-grown and X ray irradiated pure and Ce-doped LiCaAlF₆ crystals were investigated. Ce-containing samples demonstrate intensive TSL in the UV region (280-310 nm) with a main peak at 350 deg. C. It is found that the well known UV laser crystal LiCaAlF₆:Ce is a promising thermoluminescent dosimetric material. (author)

[en] A large-break loss-of-coolant accident (LOCA) was analyzed in the course of the design study for the direct-cycle supercritical-pressure light water reactor (SCLWR). The advantages of SCLWR are a higher thermal efficiency and simpler reactor system than the current light water reactors. A computer code was prepared for the analysis of the blowdown phase from the supercritical pressure. The calculation was connected to the REFLA-TRAC code when the system pressure decreased to around atmospheric pressure. The analyzed accidents are 100, 75, 50 and 25% cold-leg and 100% hot-leg breaks. First, blowdown and heatup phases without an emergency core cooling system (ECCS) were evaluated. A low-pressure coolant injection system (LPCI) was designed to fill the core with water before the cladding (stainless-steel) temperature reached a limit of 1260^oC. The LPCI consists of four units, each of which has the capacity 805 kg/s. An automatic depressurization system was designed to release the steam generated in the core in the case of cold-leg breaks and to permit operation of LPCI in the case of LOCAs of less than 100% break. For all cases analyzed, the peak cladding temperatures were lower than the limit when the designed ECCS is implemented. (author)

[en] High quality oxide bulk and fiber crystals have been successfully grown by applying advanced single crystal growth methods. REVO₄ single crystals have been grown by a modified Czochralski method in which a high temperature gradient was maintained at the interface during growth. Nd:GdVO₄ single crystals showed superior lasing properties than those of Nd:YVO₄ and Nd:YAG single crystals in slope efficiency, threshold pump power and output power. Birefringence of REVO₄ were more than 0.22. High concentration Nd³⁺ ions doped NaRE(WO₄)₂ (RE=Y, Gd) single crystal fibers were grown. Stimulated Raman scattering spectra of undoped NGW fiber was measured, and the Raman shift was observed to be larger than that of KGW. Nd³⁺ doped fibers showed superior optical properties such as high doping level and large stimulated Raman scattering shift for efficient multicolor laser. Crack-free and homogeneous K₃Li_2-xNb_5+xO_15+2x fiber crystals were grown with various pulling down rates. The crystals showed an excellent second harmonic generation properties. (orig.)

[en] Optically detected EPR investigations have been performed on the recombination luminescence (RL-EPR) of LiBaF₃ crystal, X-irradiated at T=4.2 K. RL-EPR lines of V_K- centres were found, as well as further lines of a defect with S=((1)/(2)) and an axial g-tensor with its main axis along a [1 0 0] direction of the crystal. Measurements of the magnetic circular dichroism of the absorption (MCDA) have been performed on LiBaF₃ crystals X-irradiated at two temperatures (4.2 K and RT). After irradiation at T=4.2 K, the main MCDA bands peak at 453 and 500 nm, but after irradiation at T=300 K, the main bands peak at 444 and 390 nm, there is a change of the sign between the peaks in both cases. The MCDA-detected EPR (MCDA-EPR) consists of one broad EPR line in both cases and belong to electron trap centres. Analysis of half-widths of MCDA-EPR lines showed that both defects should have g-tensors with their axes along the [1 0 0] direction. This symmetry has to be expected for F-type centres in LiBaF₃ crystals. The low-temperature electron centre has a more perturbed ground state as the RT centre

[en] Absorption, photo- and radioluminescence spectra have been investigated for as-grown and irradiated LiCaAlF₆:Eu crystal. Eu²⁺ ions markedly over lap. Irradiation induces Eu³⁺→Eu²⁺ transition and F-centers formation. Color centers destruction in the process of crystal annealing is accompanied by thermostimulated luminescence (peaks at 340, 420 and 490 K) with the typical for Eu²⁺ ion emission (370 nm). Scintillation light output is defined by the thickness of sample, Eu²⁺ concentration and contribution of factors, controlling Eu³⁺↔Eu²⁺ transformation in LiCaAlF₆:Eu

[en] The creation of radiation defects in LiBaF₃ crystals at 10 K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K. Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20 K arises from the delocalization of H-centers. The presence of two TSL peaks related to V_K-centers at 105 and 130 K indicates that 60 deg. and 90 deg. migration hops occur

[en] Absorption, emission and thermoluminescence (TL) of as-grown and X-irradiated pure and Ce-doped LiCaAlF₆ (LiCAF) and LiSrAlF₆ (LiSAF) crystals have been analyzed. It is shown that the energy storage is defined by the dissimilarity of basic matrix properties, intrinsic defect structure, preferred Ce³⁺ ion disposition and charge compensation defect type. This is the reason of higher colorability and TL efficiency of as-grown Ce:LiSAF compared to Ce:LiCAF. Pre-filling of ultra-deep traps leads to enormous increases in the TL response. Due to these properties Ce:LiSAF and Ce:LiCAF are promising thermoluminescent dosimetric materials

[en] Scintillation properties of LiCaAlF₆:Ce crystal, well known as the effective UV laser material, is reported. Ce³⁺ emission at 286-305 nm with a single exponential decay time of 35 ns provides a scintillation pulse. Radiation damage in pure and Ce-doped crystals is studied. In contrast to the majority of fluoride crystals, cerium is responsible for the ultradeep traps formation revealing thermostimulated luminescence. Overlapping of color center absorption and Ce³⁺ ion emission bands limits the scintillation efficiency of LiCaAlF₆:Ce at high radiation doses

No abstract available