Fluvio-mechanical resetting of the Al and Ti centres in quartz

ESR dating of fluvial terraces is usually based on the assumption of sunlight resetting of the Al centres in quartz. Very long bleaching times (months of sunlight exposure) are required to reset this centre to a stable, non-zero ESR intensity. Considering that highly light sensitive optically stimulated luminescence (OSL) analyses of fluvial samples often indicate partial bleaching, ESR dating should be extremely difficult. Two samples were analysed, a fluvial sediment from a Chinese river terrace and an Australian granite. Using a Höhnle sunlight simulator, the Ti centres of both samples were completely bleached within 1 to 65 h, while the Al centre required extreme bleaching times to reach stable residual intensities (∼1000 h). As an alternative to light resetting, tumbler experiments were carried out to simulate fluvial action. The samples were treated under OSL sample preparation conditions. After relatively short tumbling times, corresponding to a few km of fluvial transport, both Al- and Ti-centres were partially reset. In a granite sample, the tumbling reduced the intensity of the Al centre more effectively than light exposure.     

Arresting photodegradation of porous silicon by a polymer coating

Light soaking in air rapidly decreases photoluminescence (PL) of porous silicon (PS) and increases electron spin resonance (ESR) signal. In vacuum, a short light exposure (<2700 s) increases PL and decreases ESR, but longer exposures again degrade the PL. We could arrest the light-induced degradation over long periods by applying a thin polymer coating, which resulted in constant PL and ESR intensities. The PL intensity of coated PS is comparable to the PL intensity of a fresh PS sample in air. FTIR spectrum suggests new bond formations at the PS/polymer interface that may be responsible for PL stability.     

Thermodynamical behavior of E′ centers in quartz from sediments: Potential for paleothermometry and geochronometry

The thermodynamical behaviors of E′ centers in 8 quartz samples from core XJ33-2-1 recovered in the Zhujiang Mouth Basin were measured by electron spin resonance (ESR) technique. The E′ ESR spectral intensity of samples before any laboratory treatment was measured and expressed asI ₁. The samples were then annealed at 300°C or 350°C for 60 min. The E′ ESR spectral intensity measured after this procedure is expressed asI ₂. The ratios ofI ₁, toI ₂ for the samples increase with the sample depth (from 320 to 3972 m), showing that there is a correlation between this ratio and the storage temperature of samples. Therefore the ratio ofI ₁/I ₂ can be used as an ESR paleothermometer. Besides the temperature, we must take into account the period of time for which the samples have been buried since their deposition, because we find that the ratiosI ₁/I ₂ (from 0.293 to 0.941) are closely related to the sediment ages (from 1.5 to 27.5 Ma), with a correlation coefficient of 0.98 or 0.99 obtained by linear or exponential regression, respectively. This relation can be explained by the increase of E′ center concentration in quartz samples with the sedimentation age.     

Continuous X-ray-induced Auger electron spectroscopy

Bremsstrahlung emission from a tungsten anode has been used, for the first time, to obtain X-ray-induced Auger electron spectra (CXAES) in a conventional X-ray photoelectron spectrometer. Auger KLL signal and background intensities obtained from a silicon—aluminium sample have been compared with those obtained un der the same experimental conditions but using a standard aluminium anode. For such an aluminium anode, the respective contributions of the bremsstrahlung and the characteristic radiation to the C_KVV intensity have also been established.     

拉曼高光谱成像系统中光在奶粉层的穿透深度研究

拉曼高光谱成像技术不仅可以获取样本的空间分布信息,图像上每个像素点还包括了完整的光谱信息,因其信息量丰富的特点已在食品安全检测方面得到了应用。本研究探索拉曼高光谱成像系统中光在奶粉层中的穿透深度,以及采集参数和奶粉类型对穿透深度的影响。实验选取均匀奶粉层样品放置于厚度为5 mm的三聚氰胺样本之上,检测奶粉层厚度为0.8～4.0 mm时的三聚氰胺特征峰强度,以此评估光在奶粉层中的穿透性和信号衰减情况。结果显示当奶粉层厚度一定时,随着激光功率变大,拉曼特征峰值随之增加,此外更长的曝光时间也可以使拉曼信号得到增强。在激光功率不小于2 W且曝光时间不小于500 ms时,光在全脂奶粉层的穿透深度可达4 mm。奶粉层厚度在0.8～4.0 mm范围内,穿透奶粉层的拉曼信号随着奶粉层厚度增加呈指数式衰减。在激光功率为8 W、曝光时间为1 000 ms的条件下,光在全脂、低脂和脱脂奶粉层的穿透深度均达到了4 mm。在相同测量厚度下,通过脱脂奶粉层接收的拉曼信号弱于通过全脂和低脂奶粉层接收的拉曼信号强度。研究结果为拉曼高光谱检测中奶粉样品的前处理提供了有益参考。     

基于紫外荧光技术的柴油机润滑油被燃油稀释的检测研究

针对柴油机润滑油被燃油稀释的状态监测的问题,研究了基于紫外荧光技术的柴油机润滑油被燃油稀释的检测方法,设计搭建了检测实验装置。利用峰值发射波长为365 nm的紫外LED作为发射光源,发射的紫外光通过400 nm低通滤光片过滤后进入石英比色皿中的油样,并激发油样产生荧光,产生的荧光通过400 nm高通滤光片过滤后,利用探测波长范围为400～800 nm的光电传感器采集油样的荧光信号,利用万用表读取油样的荧光强度。设计开发了信号的放大和测量系统。高、低通滤光片的组合使用,减少了紫外光源所发射的紫外光对油样的荧光强度测量的干扰。利用该实验装置,测量了润滑油中柴油含量分别为20.3 Wt.%,10.0 Wt.%,5.0 Wt.%,2.5 Wt.%,1.5 Wt.%和0.7 Wt.%以及不含柴油的空白油样的荧光强度,经拟合得到柴油含量与荧光强度的方程。最后,为了检验该方法测量润滑油中柴油含量的准确性,采用柴油含量为7.5 Wt.%油样进行验证,利用该实验装置,测量了验证油样的荧光强度,代入拟合方程,计算得到油样中的柴油含量,结果表明通过该方法测量的油样中柴油含量与油样的实际柴油含量的相对误差为0.5%,实现了实验室条件下润滑油被燃油稀释的精确测量。     

Electrically Detected Magnetic Resonance Signal Intensity at Resonant Frequencies from 300 to 900 MHz in a Constant Microwave Field

A method for electrically detected magnetic resonance (EDMR) measurement at different ESR frequencies under a constant alternating magnetic field has been established wherein the accurate relationship between EDMR signal intensity (from a photoexcited silicon crystal and a silicon diode) and a resonant frequency of 300 to 900 MHz (UHF band) was systematically clarified. EDMR signal intensity from a photoexcited silicon crystal against a resonant frequency fitted the curve of y = a(1 - e(-bx)) well, which approached a constant value at higher frequencies. The increase in the EDMR signal intensity from the silicon diode at higher resonant frequencies was smaller than that from the photoexcited silicon crystal. The difference can be explained by the influence of the skin effect; i.e., the microwaves do not penetrate deep into a highly conductive sample at higher frequencies. EDMR signal intensities of samples vs microwave power were measured at 890 MHz. The EDMR signal intensity from the silicon diode continued to increase as the microwave power was increased, while the signal intensity from the photoexcited silicon crystal saturated within the range. The difference can be similarly explained: due to the skin effect, the microwaves gradually penetrate into the silicon diode as the power increases, so that even when saturation has been reached outside, the microwave field inside the diode does not reach the saturation level.     

Identification of irradiated rice noodles by electron spin resonance spectroscopy

Electron spin resonance (ESR) spectroscopy has been applied to the identification of the irradiation of a wide variety of foods. In this study, ESR was applied to identify irradiated rice noodles. A detailed ESR investigation of irradiated noodles was carried out in the dose range 0.5–3 kGy. The stability of the radiation-induced ESR signal at cold (?4 °C) and room (25 °C) temperatures was studied over a storage period of 24 weeks. Irradiated rice noodle samples exhibited a strong, symmetric doublet ESR signal centered at g = 2.0, whereas unirradiated noodle exhibited a very weak signal. The ESR signal intensity increased linearly with radiation dose ranging from 0.5 to 3 kGy. Keeping the samples at ?4 °C and 25 °C for 24 weeks caused decreases of 50% and 90% in the ESR signal intensities, respectively. However, long-term decay data at room temperature showed that the ESR technique could be used to identify irradiated rice noodles up to 24 weeks following irradiation.     

Characteristics of LM-OSL from several different types of quartz

We present Linear-Modulation OSL (LM-OSL) curves from several different types of quartz, including sedimentary quartz, bulk rock crystal and synthetic quartz. The LM-OSL method consists of linearly increasing the intensity of the stimulation light while continuously monitoring the OSL emission from the sample. With this technique, one obtains peaks of luminescence intensity versus time (Bulur, 1996) in which the position of the peak is inversely related to the photoionization cross-section of the trap. The shape of the LM-OSL curve is directly related to the shape of the conventional OSL decay curve in which the stimulating light source is maintained at constant intensity (so-called Continuous-Wave OSL, or CW-OSL). In the latter, the OSL from the traps with the highest photoionization cross-section decays most rapidly with stimulation time, while OSL from those traps with smaller photoionization cross-sections is characterized by longer decay times. In this paper, data are presented comparing the CW-OSL and LM-OSL curves for several different quartz types with particular focus on the changes in the shapes of each of these curves with sample type pre-heat temperature, and measurement temperature. Several different LM-OSL components are found for each sample, each with different photoionization cross-sections, but a universal behavior for quartz is not observed; each sample is different. From the dependence upon pre-heat temperature, features associated with shallow traps can be identified. Traps which empty very rapidly can be observed more easily in the LM-OSL curves than in the conventional CW-OSL curves, and the temperature dependence of the photoionization cross-section for the various components can be clearly discerned.     

TXRF and ICP-OES analysis of liquid-phase laser-ablated (LP-LA) nanoparticles of cryolite-alumina solutions

A new procedure with minimum sample preparation has been developed for a fast and serial analysis of cryolite with varying concentrations of dissolved alumina by liquid-phase laser ablation followed by Total Reflection X-Ray Fluorescence and induced coupled plasma optical emission spectroscopy. The analysis supplies the sodium/aluminium ratio of bath samples taken from industrial Hall-Herault reduction cells, as well as trace element relative concentrations. Two different types of molten samples taken directly from the aluminium production plant were placed under distilled de-ionized water in a quartz cell and subjected to pulsed laser ablation using the beam from a third harmonic Nd:YAG laser. Scanning electron microscopy examination shows the nanoparticles nature of the ablated material. The water-suspension is deposited on quartz reflectors for Total Reflection X-ray Fluorescence analysis or directly aspirated to the induced coupled plasma yielding the aluminium and sodium signals. Instrument quantification of the elements is performed by the use of aqueous standards. Validation tests were done with cryolite sample digestion and standard methods of sample quantification. The procedure can provide the aluminium/sodium ratio with adequate precision for aluminium production plant cell diagnostics and reveals the trace elements that could be considered as contamination.     

Influence of the diameter and wall thickness of a quartz pipe inserted in the EPR cavity on the signal intensity

Some dependences between the EPR signal intensity of point samples and the diameter and wall thickness of the quartz tubes with which a standard rectangular TE₁₀₂ EPR cavity is loaded are reported. It is found that the EPR signal intensity linearly depends on the wall thickness of the container and can be increased approximately twice when thick sample tubes are used. The microwave power in the location of the sample increases similarly whereas the normalized bell-shape distribution of the signal intensity along thez-axis of the cavity remains unchanged. The effective microwave power necessary to saturate the sample decreases and the cavity filling factor increases.     

Optically stimulated luminescence from quartz measured using the linear modulation technique

The optically stimulated luminescence (OSL) from heated natural quartz has been investigated using the linear modulation technique (LMT), in which the excitation light intensity is increased linearly during stimulation. In contrast to conventional stimulation, which usually produces a monotonically decreasing signal, linearly increasing the stimulation power gives peaks in the signal as a function of time. In cases where the OSL signal contains more than one component, the linear increase in power of the stimulation light may result in a curve containing overlapping peaks, where the most easily stimulated component occurs at a shorter time. This allows the separation of the overlapping OSL components, which are assumed to originate from different traps. The LM-OSL curve from quartz shows an initial peak followed by a broad one. Deconvolution using curve fitting has shown that the composite OSL curve from quartz can be approximated well by using a linear combination of first-order peaks. In addition to the three known components, i.e. fast, medium and slow components from continuous-wave-OSL studies, an additional slow component is also identified for the first time. The dose responses and thermal stabilities of the various components are also studied.     

Emergency OSL dosimetry with commonplace materials

Several commonplace materials were studied as possible emergency optically stimulated luminescence (OSL) dosimeters. The materials included: paper currency (banknotes) and coins of different denomination and from different countries; plastic cards of different types (credit and debit cards, driver's license cards, membership cards, etc.), parts and details of clothing and shoes as well as samples of different fabrics.The samples displayed significant variability in their OSL properties. They differed in the intensity of the initial ‘native’ signal; the bleaching time of the OSL signal; the sensitivity to light of different wavelengths; the fading rate of OSL signals, etc. Procedures of OSL analysis were proposed to account for this variety.Values of the minimum measurable dose (MMD) were below 2 Gy for most tested samples if OSL measurements were conducted within one week of exposure and the samples were kept in dark since exposure (except samples of shoes that were kept under environmental light).The OSL signals in banknotes appear to originate from compounds containing aluminum, silicon, calcium and titanium – these elements were detected using X-ray microanalysis. For coins, the source of the OSL signals is speculated to be small particles of quartz, which were detected on the coins' surfaces. The X-ray microanalysis spectra from fabrics and shoes revealed sodium, aluminum, titanium, iron and nickel as elements that appeared to be responsible for the radiation sensitivity of those samples.It was concluded that, under certain constrained circumstances, paper and metallic money, personal plastic cards, clothing and shoes could be used as emergency OSL dosimeters in triage applications.     

Impurity levels of iron-group ions in TiO2(II)

Photocurrent measurements on oxidized, single-crystal TiO₂ undoped and doped with V, Cr, Mn or Fe were made both before and after exposure to white light from a tungsten lamp; they revealed a band of states centered at 2.0 eV below the conduction-band edge E_c that appears to be the band of surface states active in the photoelectrolysis of water. They also revealed a band of bulk states extending from near the valence-band edge E_v to about 1.9 eV below E_c. The ESR signals from V⁴⁺, Cr³⁺ and Fe³⁺ ions in oxidized samples and from Mn³⁺ ions in reduced samples were measured before and after exposure to white and monochromatic light; changes in the ESR signal intensities allow placement of the V⁴⁺: d¹ level about 2.1 eV below E_c, the Cr³⁺: d³ level about 2.7 eV belo E_c, the Fe³⁺ level at or just below the valence band edge E_v which is 3.0 eV below E_c, the Fe²⁺ level approximately at E_c, the Mn³⁺ level about 1.9 eV below E_c. Comparison of experiments on oxidized and reduced samples suggests that the bulk states are associated with cation vacancies, and measurements with polarized light gave anisotropies that are qualitatively interpretable with a cation-vacancy model for the oxidized samples.     

Influence of the movement of cylindrical samples with variable internal diameter and variable length along thex-axis of a double TE104 and a single TE102 rectangular cavity on the EPR signal intensity: A sample shape study

The response of the cavity to the movement of cylindrical samples with internal diameters from 0.7 to 4 mm and lengths from 5 to 50 mm along thex-axis of the Bruker double TE₁₀₄ and single TE₁₀₂ rectangular cavity has been analyzed. Independently of sample internal diameter, the experimentally observed dependences of the electron paramagnetic resonance (EPR) signal intensity versus sample position in the cavity showed the following: (i) a sharp maximum for sample lengths from 5 to 20 mm; (ii) a “plateau”, over which the signal intensity remained constant within experimental errors of 0.47–1.16%, for lengths from 30 to 40 mm; and (iii) a “sloping plateau” region, which could be approximated by the linear function (correlationr = 0.96–0.98) for the 50 mm sample. Theoretical predictions of the experimental dependences of the signal intensity versus sample position in the cavity were calculated with the “modified” and “revised” sine-squared function, and the correlation between observed and theoretically computed dependences is very good. Additionally, the experimental dependence of the signal intensity versus the sample internal diameter and length for cylindrical samples situated at the position in the cavity at which the signal intensity was a maximum was likewise numerically approximated by the surface fitting with the Lorentzian cumulative additive function (correlationr = 0.999). The experimental dependence of the signal intensity versus the sample internal diameter for the given sample length is nonlinear. The samples with internal diameters of 0.7 and 1 mm gave the total maximum of signal intensity for the 40 mm sample, however, the samples with internal diameters of 2, 3 and 4 mm gave the total maximal value of signal intensity, which was identical for both the 30 and 40 mm samples. The experimental dependence of the EPR signal intensity versus the sample volume clearly showed that the samples with identical volumes, however, with different shapes, can give significantly different signal intensities (with differences ca. 200–400%). Then, the comparison of cylindrical samples with identical volumes but different shapes may be a serious source of significant errors in quantitative EPR spectroscopy. Cylindrical samples to be compared should be of identical shape. Accurate and precise positioning of each sample in the microwave cavity is essential.     

Recovering laboratory doses using fine-grained quartz from Chinese loess

Here we report the results of dose recovery experiments carried out on fine-grained quartz from a Holocene sample in Chinese loess. Optical bleaching prior to giving a 9.35 Gy dose in the laboratory was carried out using artificial light sources, namely blue light emitting diodes (LEDs) and a solar simulator, followed by more than 24 h storage at room temperature. Stimulating the quartz with blue LEDs at room temperature resulted in overestimation of the recovered dose, whereas using the same stimulation time at temperatures above 150 °C resulted in the correct value for the recovered dose. Exposure to the solar simulator for times less than 200 min resulted in overestimation of the dose, whereas progressive underestimation was found for longer bleaching times. When doses of up 5333 Gy were given ahead of a 200 min exposure to the solar simulator, the dose recovered depended upon the magnitude of the previous dose, thus questioning the general application of a simple dose recovery experiment.     

A Al MAS, MQMAS and off-resonance nutation NMR study of aluminium containing silica-based sol-gel materials

Aluminium containing hybrid materials were prepared via the sol-gel method using aluminium sec-butoxide complexed with ethylacetoacetate (Al(OBu^s)₂EAA or Al(OBu^s)₃/EAA mixtures). As silanes, phenyltrimethoxysilane (PhTMS) or phenyltriethoxysilane (PhTES), 3-glycidoxypropyl trimethoxysilane (Glymo) and tetraethylorthosilicate (TEOS) were used. After room temperature drying of the samples the ²⁷Al single pulse excitation (SPE) magic angle spinning (MAS) NMR shows that octahedral (5 ppm) and tetrahedral (55 ppm) coordinated aluminium species are present in the materials. The relative amount of these two species depends on the preparation method. However, the Al(IV)/Al(VI) ratio is lower than 3 (typically 2.3) in all materials, indicating the presence of a small amount of an aluminate phase. Annealing of the samples at 100, 150 and 200 °C results in the formation of an extra signal at 30 ppm (peak maximum measured at 11.7 T). Based on the resonance frequency this signal is generally assigned to a pentahedrally coordinated aluminium species. Hydration/dehydration processes of annealed samples were studied with ²⁷Al SPE MAS NMR, multiple-quantum MAS NMR (MQMAS) and off-resonance nutation NMR. Upon hydration of the annealed sample the signal intensity around 30 ppm decreases in intensity and at the same time the intensity of the signal around 55 ppm increases by the same amount (tetrahedrally coordinated aluminium). The MQMAS spectra reveal that the signal around 30 ppm is not caused by a fivefold-coordinated aluminium species but mainly by tetrahedrally coordinated aluminium species in a distorted environment, experiencing large quadrupole induced shifts and small chemical shifts due to conformational changes in the polymeric network. From the MQMAS NMR spectra it can be concluded that the linebroadening observed in the ²⁷A1 MAS NMR spectra is due to both a distribution in isotropic chemical shifts and a distribution in quadrupole coupling constants (C_qcc = e²qQ/h). Hydration of the sample results in a decrease of the average C_qcc for the tetrahedrally coordinated aluminium from 6 to 4 MHz, whereas the average C_qcc of the octahedrally coordinated aluminium is hardly influenced (4 MHz). These MQMAS results are confirmed by off-resonance nutation experiments.     

ESR and TL studies of irradiated Anatolian laurel leaf (Laurus nobilis L.)

Laurel leaf (Laurus nobilis L.) samples that originated from Turkey were analyzed by electron spin resonance (ESR) and thermoluminescence (TL) techniques before and after γ-irradiation. Unirradiated (control) laurel leaf samples exhibit a weak ESR singlet centered at g=2.0020. Besides this central signal were two weak satellite signals situated about 3 mT left and right to it in radiation-induced spectra. The dose–response curve of the radiation-induced ESR signal at g=2.0187 (the left satellite signal) was found to be described well by a power function. Variation of the left satellite ESR signal intensity of irradiated samples at room temperature with time in a long term showed that cellulosic free radicals responsible for the ESR spectrum of laurel leaves were not stable but detectable even after 100 days. Annealing studies at four different temperatures were used to determine the kinetic behavior and activation energy of the radiation-induced cellulosic free radicals responsible from the left satellite signal (g=2.0187) in laurel leaves. TL measurements of the polymineral dust isolated from the laurel leaf samples allowed distinguishing between irradiated and unirradiated samples.     

远距离探测拉曼光谱特性

为了发展远距离探测未知或危险物质的方法, 设计并建立了近同轴可见光远距离拉曼光谱探测实验装置, 对硝酸盐固体样品进行了距离为2-10 m的拉曼光谱测量, 初步研究了拉曼信号强度与激发光功率、探测距离、样品浓度及样品表面方向之间的关系. 实验观察到三种硝酸盐在1050 cm^-1附近的拉曼谱线, 其微小的差异可作为识别特征. 硝酸铵的特征拉曼谱线强度正比于激发光功率, 近似平方关系; 与探测距离之间趋向于二次反比关系; 与样品浓度接近指数关系; 与样品表面朝向有近似余弦函数的关系.     

In VivoLongitudinally Detected ESR Measurements at Microwave Regions of 300, 700, and 900 MHz in Rats Treated with a Nitroxide Radical

A signal detector of longitudinally detected ESR (LODESR) is independent of the resonant frequency. We developed anin vivoLODESR spectrometer operating in the regions of 300, 700, and 900 MHz. Using this apparatus, we estimated signal intensities at different operating frequencies obtained from non- or high-dielectric loss phantoms that contained nitroxide radical solutions and from live rats that had received a nitroxide radical. Our result, higher signal intensities in the high-dielectric loss samples (such as physiological saline solution and animals) at a lower frequency, shows that the influence of a decrease in dielectric loss dominates over the signal reduction caused by smaller Zeeman splitting. We believe that this finding strongly supports anin vivoESR resonant frequency that tends to be low.