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981.
Winoto S. H. 《显形杂志》2004,7(3):257-262
The 7th Asian Symposium on Visualization (7ASV) was successfully held in Singapore from 3rd to 7th November 2003. This event was originally scheduled from 26th to 30th May 2003, but had to be postponed because of the outbreak of SARS (Severe Acute Respiratory Syndrome) in some parts of the
world. A total number of 122 participants attended the Symposium of which, 107 were foreign participants from 16 countries
(excluding Singapore) worldwide. There were 104 papers covering broad range of topics presented at the Symposium which were
delivered in 2×7 long sessions, and 9 keynote papers. 相似文献
982.
S. Burachas S. Beloglovsky D. Elizarov I. Makov Yu. Saveliev N. Vassilieva M. Ippolitov V. Manko S. Nikulin A. Nyanin A. Vasiliev A. Apanasenko G. Tamulaitis 《Radiation measurements》2004,38(4-6):367-370
Technological conditions ensuring growth of optically homogeneous lead tungstate (PWO) crystals are reported. It is shown that the basic scintillator characteristics of PWO grown from highly purified raw material and properly doped with lanthanides are mainly determined by inclusions of oxides W1−yLyO3−x (L=Y, La, Gd; 0<x<0.3). Moreover, surface-located inclusions with structure close to tungstenite may also be of importance. It is demonstrated that the scintillation properties can be intentionally designed by varying the oxygen content in the inclusions x and the surface structure. The optimal value for x and the most favorable surface structure are achieved by proper thermal regimes and environment content during the crystal annealing. The results enabled low-cost fabrication of PWO scintillators with steady and reproducible characteristics acceptable for the CERN project ALICE and ensured production of PWO on an industrial scale by “North Crystals” company at a rate of 125–135 crystals per year from every growth apparatus. 相似文献
983.
A. Edgar G. V. M. Williams M. Secu S. Schweizer J. -M. Spaeth 《Radiation measurements》2004,38(4-6):413-416
The turbidity, photoluminescence, and photo-stimulated luminescence (PSL) of fluorozirconate glass containing barium chloride nano- and micro-crystals have been measured for samples prepared by isochronal (70 min) annealing over a temperature range of 220–283°C, and correlated with the microstructure as determined by X-ray diffraction measurements. Crystallization of hexagonal phase barium chloride commences at around 220°C, but until 275°C the material retains excellent transparency although it displays negligible PSL. Between 275°C and 277°C, the hexagonal phase converts to the orthorhombic phase, the transparency abruptly decreases, and the PSL rises to a value of around 13% of that found for the commercial storage phosphor BaFBr:Eu. For a slightly higher temperature of 280°C, new phases appear which correspond to the onset of bulk crystallization, and at 283°C the relative PSL rises to 33%, while the transparency falls further. The trade-off between optical transparency and PSL over this narrow temperature window for X-ray imaging plate applications is briefly discussed. 相似文献
984.
N. Shiran A. Gektin S. Neicheva V. Voronova V. Kornienko K. Shimamura N. Ichinose 《Radiation measurements》2004,38(4-6):459-462
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. 相似文献
985.
The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al2O3 dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al2O3 single-crystal chips, of the type usually known as TLD-500, and LuxelTM dosimeters (Al2O3:C powder in plastic) from Landauer Inc. The samples were exposed to 4He (150 MeV/u), 12C (400 MeV/u), 28Si (490 MeV/u) and 56Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/μm in water and doses from 1 to 100 mGy (to water). A 90Sr/90Y beta source, calibrated against a 60Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (ηHCP,γ) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or LuxelTM) and the luminescence method used to define the signal—i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al2O3 in the areas of space radiation dosimetry and radiation oncology. 相似文献
986.
I. I. Milman E. V. Moiseykin S. V. Nikiforov S. G. Mikhailov V. I. Solomonov 《Radiation measurements》2004,38(4-6):443
The spectra of pulsed cathodoluminescence (PCL) and thermoluminescence (TL) in TLD-500 detectors, which were exposed to a strong beam from a pulsed electron accelerator, have been studied. Additional bands in the PCL spectrum and new peaks in the TL curves, which are due to impurity ions, have been revealed. Luminescence bands of F- and F+-centers cannot be used in the dosimetry of strong electron beams using TLD-500 detectors because of the saturation of dose dependence and the decrease in the TL yield. It is shown that high doses from these beams can be measured by recording TL in the luminescence band of impurity titanium ions. 相似文献
987.
S. Sasa A. Nakashima Y. Nakajima M. Inoue 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):224
We fabricated nanoscale open-dot structures in an InAs surface inversion layer using an atomic-force-microscope oxidation process. Due to its superior nanofabrication capability, small open-dot structures with the feature size ranging between 100 and 300 nm were successfully fabricated. The magnetoresistance signal measured at 4.2 K showed reproducible fluctuations and a periodic oscillation component that varies in both amplitude and periodicity depending on the dot size. We show that the period of the oscillations corresponds to that of the Aharonov–Bohm effect and propose that the possible mechanism for the oscillations is due to the formation of a one-dimensional electron channel enclosing the open-dot structure as a result of the electron transfer from the InAs oxide to InAs. 相似文献
988.
K. Suzuki S. Miyashita K. Takashina Y. Hirayama 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):232
We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer-νnet discontinuous. Under tilted magnetic fields, these Rxx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings. 相似文献
989.
S. Schweizer M. Secu J. -M. Spaeth L. W. Hobbs A. Edgar G. V. M. Williams 《Radiation measurements》2004,38(4-6):633-638
We found a significant PSL effect in Eu2+-doped fluorozirconate glasses (ZBLAN) which were additionally doped with Br− or Cl− ions. The PSL is attributed to the characteristic emission of Eu2+ present in nano-crystallites of BaBr2 or BaCl2, which form in the glass upon annealing. The metastable hexagonal form of BaX2 (X=Br,Cl) is always formed first before it is converted into the stable orthorhombic form. The particle size increases upon annealing and so does the PSL efficiency of the glass ceramic. However, there is a saturation of the PSL efficiency, which is for Br− doping about 9% and for Cl−-doping about 80% of the Eu-doped BaFBr standard. The particle size was determined by transmission electron microscopy (TEM). The TEM results show a clear tendency for bigger particles for longer annealing at the expense of its number. The particle size for the most efficient phosphor is about 100 nm. 相似文献
990.
The thermally stimulated properties of PbWO4 in the temperature range 90–400 K have been investigated on undoped and terbium-doped crystals after X-ray irradiation at 90 K. Doping with terbium changes the concentration of shallow traps, which are responsible for retrapping free electrons and holes. Light illumination can change the distribution of the traps. The optically stimulated luminescence is observed. The influence of light illumination on the TSL curves and emission properties is studied. The possible mechanism of TSL phototransformation is discussed. 相似文献