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X-波段电子自旋成象 总被引:3,自引:3,他引:0
报道了自行设计研制的X-波段ESR成象装置并用之对典型样品作了ESR成象测定;用解卷积和分析图象重建中卷积滤波法对自旋样品体系进行了二维的图象重建,获取了能反映真实自旋分布的二维自旋密度图象. 相似文献
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用电子自旋共振(ESR)方法对非晶Ag+离子导体0.85AgI~0.15Ag4P2O7的热处理晶化过程进行研究,在样品中掺入微量(约1×10-3 g/g)的Mn2+或V4+离子作为自旋探针离子,它们的ESR谱强度随升温线性减弱,当样品完全晶化时ESR谱消失。这样测定的样品完全晶化的温度分别为98℃(掺Mn的)和108℃(掺V的).本文还对Mn2+和V4+的ESR谱进行了分析。 相似文献
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在与晶粒组元相当的包裹纳米FeAl晶粒的无序界面或/和表面组元中,存在Fe-Al-Fe电子的超交换作用或/和Fe-Fe交换作用,使多晶FeAl合金因晶粒纳米化出现非磁性—磁性转变.X波段(频率为9.48GHz)的电子自旋共振(ESR)实验表明多晶FeAl合金没有磁共振信号.纳米晶样品的铁磁共振(FMR)信号是一个线宽ΔHpp为8×104A/m以上的宽峰.还观测到纳米晶体样品中Fe2+离子的ESR精细结构双峰,两峰间隔为1.316×10关键词: 相似文献
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纳米NiAl的电子自旋共振研究 总被引:2,自引:1,他引:1
对纳米NiAl样品进行电子自旋共振(ESR)研究时发现晶粒尺寸效应产生的非磁-磁性转变.大块多晶NiAl合金的没有ESR信号,只有很弱的Pauli顺磁性.而粒径为8.6nm的纳米NiAl样品的ESR信号,随温度的增高而显著下降,其居里温度TC为124K,在室温下ESR信号很弱.8.6nm的纳米NiAl样品经550℃和707℃退火处理后得到粒径分别为12nm和21nm的两个样品,它们在室温下都有较强的ESR信号,并能够被永磁体吸起。多晶NiAl合金与纳米NiAl之间存在非磁-磁性转变, 相似文献
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迄今未见任何稀土氨基酸络合物的ESR波谱报道,本文在合成Gd3+分别与甘氨酸、β-丙氨酸、谷氨酸、天冬氨酸和天冬酰胺五种氨基酸络合物的基础上,测定了不同温度下,水溶液、粉末及分子筛吸附样品的ESR谱,讨论了络合物中晶体场强,对称性及成键特性。 相似文献
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对来自坦桑尼亚Merelani地区的坦桑石样品,分别采用电子探针、EMXPLUS型ESR谱仪、同步热分析仪、紫外可见光谱仪以及傅里叶变换红外光谱仪进行了测试与分析。结果表明:坦桑石样品的主要成分为SiO2,Al2O3和CaO,微量成分中V2O5含量相对最多,平均含量为0.36%;坦桑石样品本身不含吸附水,结晶水, 加热至780 ℃附近时,脱失结构水,样品中结构水大约占总质量的2%;ESR实验结果中显示出明显Fe3+和Mn2+的电子顺磁信号;紫外-可见光谱显示,样品在385 nm处出现吸收窄带,575和750 nm处分别出现较为宽缓的吸收;红外光谱测试表明,样品在6 500~9 000 cm-1波段的倍频振动区,基本没有吸收。在4 000~6 500 cm-1波段主要为和频振动,5 956 cm-1附近呈较宽缓的吸收峰,5 413,5 184,4 336和4 046 cm-1处出现较尖锐的吸收峰,主要可能由O-H,矿物内的Si-O,以及空气里面的H2O分子和CO2振动所引起。综合EPMA以及ESR分析结果,蓝-紫色坦桑石颜色可能主要由V3+和V5+共同引起,Fe3+晶体场的d-d电子跃迁、Fe2+→Ti4+的电荷转移辅助致色。 相似文献
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In this paper, a method for identifying interfering EPR signals in fossil tooth enamel is presented. This method consists of optimizing EPR parameters to enhance spectral resolution of the fossil signals followed by a g-factor and intensity normalized subtraction of a high-dosed, modern tooth enamel sample spectrum. By scanning the modern tooth enamel sample with the same parameters as the fossil sample, the difference spectrum of the fossil and modern irradiated tooth enamel samples can resolve numerous hyperfine and other interfering signals. This method was successfully applied to a fossil sample studied elsewhere (Grün, R., 1998a. Ancient TL 16, 51–55; Grün, R., Clapp, R., 1996. Ancient TL 14, 1–5; Martin Jonas, 1997. Ph.D. Thesis, Cambridge University; Jonas, M., Grün, R., 1997. Radiat. Meas. 27, 49–58; Vanhaelewyn et al., 2000. Appl. Radiat. Isot. 52, 1317–1326). This sample has shown discrepancies in dose estimations obtained from the power absorption curve versus those obtained from the first derivative spectra (Grün, R., 1998b. Radiat. Meas. 29, 177–193). The reason for this, and other discrepancies, are accounted for by the signals resolved using the method presented here. 相似文献
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Radiation-induced growth in the g = 2.0018 signal in fossil tooth enamel can be used to determine the age of fossil teeth. Porat and Schwarcz (1994) [Integrative Paths to the Past: Paleoanthropological Advances in Honor of F.C. Howell (eds Corrucini R. and Ciochon R.), pp. 521–530. Prentice- Hall, Englewood Cliffs] suggested that the radiation sensitivity of all tooth enamel is quite similar, and have constructed a Universal Growth Curve (UGC) to estimate equivalent dose (DE). To further test this concept, we use a saturating exponential of the form I = Imax (1 - exp[- D/D0]) to fit normalized ESR intensity (I) data for teeth from various sites. We show that the ranges of fitting parameters Imax and D0 overlap for modern and fossil enamels. This suggests that no significant diagenetic changes in the enamel have occured to affect the ESR signal in most samples. Sensitivity, as measured by normalized intensity at D = 32 Gy, varies by 22% (n = 24); modern samples have the same mean sensitivity, but show less variation (8%). The normalized dose-response curve (natural intensity vs DE) is a good predictor of DE, although there are some outliers. Imax is strongly correlated with D0, suggesting a relationship between trap concentration and capture cross-section for migrating charges. 相似文献
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In ESR dating of Early Pleistocene fossil tooth enamel samples, the fitting function used for the evaluation of the DE value is undoubtedly among the major sources of uncertainty. Dose recovery tests performed on fossil tooth enamel showing DE values >1,000 Gy demonstrate: (i) that high precision ESR measurements (<0.5%) and high DE reproducibility (<5%) may be achieved; (ii) the appropriateness of the Double Saturating Exponential (DSE) fitting function for ESR dose reconstruction. In contrast, the SSE function, which has been almost exclusively used so far, does simply not correctly describe the behavior of the radiation induced ESR signal of tooth enamel with the dose.Several fitting functions and data weighting options were tested and the combination of a DSE with data weighted by the inverse of the squared intensities is the procedure providing the most accurate DE results. However, the SSE may nevertheless sometimes produce consistent results if Dmax does not exceed 6*DE. Further work is required in that direction in order to determine more precisely in which conditions the SSE could be used as a fair approximation of the DSE function for these samples. 相似文献
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EPR-dosimetry with carious teeth 总被引:1,自引:0,他引:1
S. V. Sholom E. H. Haskell R. B. Hayes V. V. Chumak G. H. Kenner 《Radiation measurements》2000,32(5-6):799-803
The effect of caries in EPR dosimetry of tooth enamel (in the dose range of 0–1 Gy) was investigated. The enamel of each tooth was divided into carious, non-carious and intermediate portions. The EPR signals of enamel at g = 2.0018 (dosimetric) and g = 2.0045 (native) were examined. The intensity of the dosimetric signal was the same for all three portions, while that of the native signal was higher for carious portions than for non-carious and intermediate portions. Reconstruction of the laboratory applied doses was done using all portions. Reasonable correlation between nominal and reconstructed doses was found in most cases. The effect of alkali treatment on the native and dosimetric signals of enamel was also tested. Reduction of the native signal intensity, particularly in the carious portions, was found to be the only significant effect. This resulted in a slight improvement in the accuracy of the reconstructed doses. 相似文献
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《Radiation measurements》2007,42(6-7):1185-1189
In the EPR spectra of tooth enamel samples exposed to sequential radiation and mechanical effect, the intensity of the signal in the spectra of tooth enamel samples exposed to sequential mechanical and radiation effects exceeded the amplitude of a signal in enamel samples that were only exposed to radiation. The increased dosimetric signal can be explained by superposition of mechanically and radiation-induced signals. The contribution of the mechanically induced component to the individual dose load reconstructed by EPR-spectra of tooth enamel has been evaluated. 相似文献
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The beta dose response and Optically Stimulated Luminescence (OSL) signal stability characteristics of human tooth enamel deproteinated by hydrazine reagent under blue photon stimulation are reported. Removal of the protein organic component of tooth enamel resulted in a higher OSL sensitivity and slower fading of OSL signals. The effect of chemical sample preparation on the enamel sample sensitivity is discussed and further steps to make this deproteinization treatment suitable for in vitro dose reconstruction studies are suggested. 相似文献
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Comparative EPR investigation of CO2− radicals in modern (γ-irradiated) and fossil samples of tooth enamel was performed. The samples studied were the enamel powders and plates, the latter demonstrating an orientation dependence of EPR spectra in an external magnetic field. It was found that the ratio between the axial and orthorhombic CO2− centers amounts appears to be different for modern and fossil enamels. This ratio can be estimated by modeling of EPR spectra lineshape of powders or, in the case of plates, from the orientation dependence of EPR spectra in an external magnetic field. It was assumed that the difference between modern and fossil enamels is caused by the transformation, in the course of time, of orthorhombic CO2− centers into axial ones. The equations that describe this process were deduced. Their solutions show that the ratio between the amounts of the axial and orthorhombic centers does not depend on the dose rate. This finding can be used for the development of the method to determine the fossil enamel age avoiding the determination of the annual dose. 相似文献
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The ESR spectra of a fragment of fossil tooth enamel were measured by rotating it in 10° increments over 360° around its three major axes. We used an automated simulated annealing (SA) procedure for the mathematical decomposition of the spectra. The SA approach is particularly robust in finding global solutions rather than getting stuck in local minima. All angular measurements could be fitted with four Gaussian lines, all of which could be attributed to components of CO2? radicals. The results imply that the tooth enamel fragment contains at least two different types of oriented CO2? radicals, plus about 9% of non-oriented CO2? radicals. The oriented components were tentatively attributed to axial and orthorhombic CO2? radicals. Their explicit locations in the crystal domains of the tooth enamel remain unresolved. 相似文献
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S. Onori D. Aragno P. Fattibene E. Petetti M. C. Pressello 《Radiation measurements》2000,32(5-6):787-792
The accuracy in Electron Paramagneetic Resonance (EPR) dose reconstruction with tooth enamel is affected by sample preparation, dosimetric signal amplitude evaluation and unknown dose estimate. Worldwide efforts in the field of EPR dose reconstruction with tooth enamel are focused on the optimization of the three mentioned steps in dose assessment. In the present work, the protocol implemented at ISS in the framework of the European Community Nuclear Fission Safety project “Dose Reconstruction” is presented. A combined mechanical–chemical procedure for ground enamel sample preparation is used. The signal intensity evaluation is carried out with powder spectra simulation program. Finally, the unknown dose is evaluated individually for each sample with the additive dose method. The unknown dose is obtained by subtracting a mean native dose from the back-extrapolated dose. As an example of the capability of the ISS protocol in unknown dose evaluation, the results obtained in the framework of the 2nd International Intercomparison on EPR tooth enamel dosimetry are reported. 相似文献
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调制激光作用牙齿组织发生散射形成光子密度波, 而由于光热效应产生热波, 基于一维介质辐射传输漫射近似方程与一维热传导方程建立了调制激光作用牙齿组织半透明混合介质的一维热波数学模型. 利用该模型仿真分析了牙齿龋损特性参数(牙釉质龋损层光吸收系数、散射系数、热扩散系数及龋损深度)对光热辐射动态响应特性的影响与规律. 利用红外探测器(HgCdTe, 2–12 μm)记录808 nm半导体激光激发牙齿组织产生的热波信号, 由锁相放大器计算热波信号的幅值与相位. 通过频率扫描试验获得了牙齿组织的光热动态响应, 利用多参数最佳统计拟合方法得到了牙齿组织特性参数. 结果表明光热辐射测量对牙齿组织不均匀性和龋损特性均具有较高敏感性与特异性. 相似文献