Effect of annealing temperature on determining trap depths of quartz by various heating rates method

The aim of this study is to determine the trap parameters (trap depth E, frequency factor s) of quartz using various heating rates method and also to investigate the effect of annealing temperature on determining trap depths. The method is based on the positions of the thermoluminescence peaks, obtained from the change in temperature of the peak at maximum caused by changing the heating rate at which the sample is measured. In the present work, powder quartz samples were annealed first at different temperatures before irradiation. Then samples irradiated to different doses were measured with a TL reader at different heating rates and the glow curves were recorded. In order to calculate the trap depth E and the frequency factor s, the glow parameter T_m was determined experimentally from the glow curve by measuring the shift of the maximum peak temperature depending on heating rate β. The calculation of trap parameters was repeated for each annealing temperature. Then the effect of annealing temperature on trap depths calculated by the various heating rates method was evaluated.     

The trap parameters of electrons in intermediate energy levels in quartz

The trap parameters (thermal activation energy E_t and frequency factor s) of the glow peaks of quartz, occurring in the temperature range 420–520 K and corresponding to intermediate energy levels, were evaluated using different and complementary methods of analysis: peak shift, isothermal decay and fractional glow curve. The values of E_t and of s derived with the isothermal decay method and with the peak shift technique agree quite well, within the error limits. The corresponding values obtained using the fractional glow curve analysis proved to be underestimated, probably as a consequence of the thermal quenching. Proper corrections were therefore applied to take into account this phenomenon.     

Diffusion of W on A W(211) plane

The diffusion of W on a (211) plane of a W field emitter has been re-examined by means of the fluctuation autocorrelation method. Diffusion along channels yielded E = 16.8 ± 0.5 kcal, D₀ = (3 ± 1) × 10⁻⁵ cm² s⁻¹. For diffusion across channels E =6.6 kcal, D₀ = 4 × 10⁻⁹cm² s⁻¹ at T < 752 K, and E = 24 kcal, D₀ = 5 × 10⁻⁴ cm² s⁻¹ at T > 752 K. The results for diffusion along channels yield E and D₀ values intermediate between recent results by Wang and Ehrlich [Surf. Sci. 206 (1988) 451] using field ion microscopy (E = 19 kcal, D₀ = 7.7 × 10⁻³ cm² s⁻¹) and Tringides and Gomer [J. Chem. Phys. 84 (1986) 4049], using the same method as the present work but a larger slit (E = 13.3 kcal, D₀ = 7 × 10⁻⁷ cm² s⁻¹). The results for cross channel diffus good agreement with those of Tringides and Gomer below 752 K, where these authors stopped. The new high temperature results suggest that the channel wall exchange mechanism postulated by Tringides and Gomer for cross channel diffusion at low T gives way to diffusion by climbing over the channel walls with higher E but also higher D₀ above 752 K. Possible reasons for the discrepancies between these three sets of results and the absence of cross channel diffusion in the work of Wang and Ehrlich are briefly discussed.     

Monitoring anomalous fading of TL of feldspars by using far-red emission as a gauge

TL dating of feldspars of volcanic origin is thwarted by anomalous fading of its emission in the usual spectral range from UV to red, though in the far-red range it has been shown to be stable. A new method of evaluation of this anomalous fading is proposed. The comparison is no longer made directly between total TL emissions after different storage times. Instead, TL is first measured in two spectral ranges simultaneously, the ‘blue’ one, usually monitored for fading, and the far-red one. Secondly, at every temperature the ratio of ‘blue’ to far-red, named B_ir, is computed. Thirdly, to monitor anomalous fading, these ratios are compared between different TLs. When fading shows, values of B_ir are observed to decrease during storage, according to the logarithmic law, down to very low values. A temperature dependance of anomalous fading is firmly established.     

Radiation effect on the 400-nm-thermoluminescence emission of a potassium-rich feldspar

The UV-blue thermoluminescence (TL) emission of exsolved and twinned potassium feldspars is potentially valid to be employed in the field of dating and retrospective dosimetry. This paper reports about the following results: (i) The dose dependence of the 400 nm TL intensity of a K-rich feldspar exhibits an excellent linearity in the range of 50 mGy–8 Gy. (ii) The stability of the TL signal after 6 months of storage, shows an initial rapid decay (ca. 45%) maintaining the stability from 40 days onwards which indicates that the electron population decreases asymptotically by the X-axis and the involved electrons are located in deeper traps at room temperature. The fading process can be fitted to a first-order decay equation of the sort y=y₀+A exp(−x/t). (iii) The tests of thermal stability at different temperatures confirm a continuous trap distribution with progressive changes in the glow curve shape, intensity and temperature position of the maximum peak. According to this behaviour some physical parameters are defined.     

Radiation damage in single crystal L-Histidine as studied by low-temperature thermoluminescence techniques

X-irradiation of single crystal L-Histidine at 10 K produces TL glow peaks at 38, 72, 84, 122, 162, 204, and 245 K. The 84 K peak is the most intense one and is characterized by a thermal activation energy of 0.073 eV and frequency factor of 1.1×10³s^-1. Moreover, it is readily photobleachable, whereas the other glow peaks are not, and is tentatively correlated with the thermal decay of a carboxyl anion radical. Computer simulation of the Randall-Wilkins first-order TL expression provided a check on the experimentally derived parameters characterizing the 38 and 84 K peaks. The initial-rise method did not produce accurate parameters for the 38 K peak; however, computer simulation yielded an activation energy of 0.022 eV and a frequency factor of 20 s^-1 which were in agreement with the experimental shape of the glow curve. This TL peak is attributed to the thermal destruction of an imidazole cation radical. Emission spectra measurements of the 84 K luminescence (other peaks were of insufficient intensity) indicated that TL results from thermal release of electrons and their subsequent de-excitation to the ground state via the singlet and triplet manifolds. At sufficiently high temperatures (～78 K) one only observes singlet state emission due to intersystem crossing.     

Joule–Thomson expansion of higher dimensional nonlinearly AdS black hole with power Maxwell invariant source

In this paper, the Joule–Thomson expansion of the higher dimensional nonlinearly anti-de Sitter(Ad S) black hole with power Maxwell invariant source is investigated. The results show the Joule–Thomson coefficient has a zero point and a divergent point, which coincide with the inversion temperature Tiand the zero point of the Hawking temperature, respectively. The inversion temperature increases monotonously with inversion pressure. For the high-pressure region, the inversion temperature decreases with the dimensionality D and the nonlinearity parameter s, whereas it increases with the charge Q. However, Tifor the low-pressure region increase with D and s, while it decreases with Q. The ratio ηBHbetween the minimum inversion temperature and the critical temperature does not depend on Q, it recovers the higher dimensional Reissner–N?rdstrom Ad S black hole case when s = 1. However, for s 1, it becomes smaller and smaller as D increases and approaches a constant when D →∞. Finally, we found that an increase of mass M and s, or reducing the charge Q and D can enhance the isenthalpic curve, and the effect of s on the isenthalpic curve is much greater than other parameters.     

Thermal quenching of far-red Fe3+ thermoluminescence of volcanic K-feldspars

Strong thermal quenching is observed from 77 to 550 K in the far-red luminescence of K-feldspars. This far-red emission, next to the emission in the UV-to-blue spectrum recorded for thermoluminescence (TL), is reported in most alkaline feldspars with a characteristic peak centered on 710 nm with a width of 100 nm. This emission was observed by cathodoluminescence (CL) at room temperature (RT) for more than 30 K-feldspars, ranging from volcanic sanidines to granitic microclines and sediments and it is attributed to an Fe³⁺ impurity. Contrary to ‘blue’ emission in volcanic feldspars, the far-red emission displays very low anomalous fading (AF). This makes it attractive for dating purposes; however, it has weak natural TL intensity, even at saturation, which competes with the black-body emission of the heater plate. This is in contrast to an intense tunneling afterglow at liquid nitrogen temperature (LNT). Further observations show that the disadvantage of weak TL can be overcome. Photoluminescence (PL) under UV shows a very strong thermal quenching effect of the far-red emission from 77 to 550 K, which accounts for the above contrast. Near the LNT, the far-red Fe³⁺ photoluminescence is at a maximum and is dominant over other emissions in the spectrum. However, as the temperature increases, the efficiency decreases, falling to well below one percent, whereas the ‘blue’ emissions remain stable. This thermal quenching effect in photoluminescence is paralleled in TL. After irradiation and during storage at RT, whereas the ‘blue’ emission in volcanic feldspars is affected by ‘fast’ anomalous fading, charge trapped at Fe³⁺ centers as latent far-red emission is almost stable. As the TL evolves and the extant ‘blue’ emission is emitted, more and more of the trapped charge associated with far-red emission recombines non-radiatively, resulting in an efficiency for emission in natural TL that is less than one percent. A modified band model, which calls for 'hopping' conductivity during the storage, accounts for the anomalous fading. Trap emptying at lower temperatures should lead to better use of the stable latent far-red stored charge for the dating of volcanic deposits.     

Representation surfaces of Young''s modulus and Poisson''s ratio for BCC transition metals

 The general expressions for the compliance , Young's modulus E(h k l) and Poisson's ratio υ(h k l) along an arbitrary direction [h k l] are given for cubic crystals. The representation surfaces, for which the length of the radius vector in the [h k l] direction equals to E(h k l) or υ(h k l), are constructed for seven BCC transition metals Cr, Fe, Mo, Nb, Ta, V and W. Neglecting W, which is isotropic, both representation surfaces of Young's modulus and Poisson's ratio are spherical surfaces. The remaining BCC transition metals may be grouped into two classes. In the first group (Cr, Mo, Nb and V) with negative values of s_A, Young's modulus surface has eight depressed corners and six rounded protuberances at the centers of the faces. In the second group (Fe and Ta) with positive values of s_A, on the contrary, Young's modulus surface has eight rounded protuberance corners and six depressions at the centers of the faces. The contrary conclusions are obtained for Poisson's ratio.     

Analytical result for dimensionally regularized massless master non-planar double box with one-leg off shell

The dimensionally regularized massless non-planar double box Feynman diagram with powers of propagators equal to one, one leg off the mass shell, i.e., with p₁²=q²≠0, and three legs on shell, p_i²=0, i=2,3,4, is analytically calculated for general values of q² and the Mandelstam variables s,t and u (not necessarily restricted by the physical condition s+t+u=q²). An explicit result is expressed through (generalized) polylogarithms, up to the fourth order, dependent on rational combinations of q²,s,t and u, and simple finite two- and three-fold Mellin–Barnes integrals of products of gamma functions which are easily numerically evaluated for arbitrary non-zero values of the arguments.     

使用迭代法的终止检验

为了保证使用迭代法解偏微分方程数值解时的精度,终止检验是一个非常重要的问题。当线性代数方程组的系数矩阵是严格对角优势或不可约弱对角优势时,本文给出了使用迭代法u^s+1=Gu^s+K解偏微分方程时的终止检验公式。并且还给出一些数值例子。     

Tunneling rate for superparamagnetic particles by the instanton method

We derive the tunneling rate for paramagnetic molecules in the context of a collective spin model. By means of path integral methods, an analytical expression is derived. Given the very large spins in question (s3000), the observation of magnetization changes due to pure unitary tunnel effects is unlikely.     

Lithium ion transport in germanophosphate glasses

Glasses in the system Li₂O–GeO₂–P₂O₅ have been prepared using melt quenching route. Li⁺ ion transport has been investigated in these glasses using both d.c. and a.c. conductivity measurements. Arrhenius plots of d.c. conductivity exhibits two different slopes, which has been discussed in the light of cluster-tissue model. A.c. conductivity data has been fitted to single power law. Dielectric relaxation has been analyzed based on the behaviour of moduli. Good collapse on to master plots is observed for both a.c. conductivity and moduli. The behaviour of E_dc, s and β are found to be consistent when conductivity mechanism is considered as involving NBO–BO switching as the first step, which is followed by Li⁺ ion migration.     

阶矩阵及其在传统预处理方法中的应用

本文应用矩阵元素阶和阶矩阵概念,讨论了ICCG和MICCG这两种传统的预处理方法在实用中的一些问题。为什么ICCG(s,t)在s+t固定时取(s,t)=(1,1),(1,2),(1,3),(2,4),(3,5),…有较高的收敛速度?为什么MICCG(m)当m>3时迭代次数不变?ICCG和MICCG的填入方式如何系统化?MICCG是否总比ICCG收敛速度高?本文拟作一个初步的讨论。通过LU分解的阶矩阵,本文给出了按阶递增的填入原则,将ICCG和MICCG系统化为P阶ICCG和P阶MICCG,并讨论了MICCG原有填入方式存在的问题。应用误差阵的阶矩阵,本文讨沦了MICCG迭代参数选取中存在的问题,给出了合理的参数选取方法。通过不同算例,本文还比较了ICCG和MICCG的计算效率。     

Comparison of ‘blue’ and ‘infrared’ emission bands in thermoluminescence of alkali feldspars

Dating quaternary sediments by thermoluminescence (TL) or optically stimulated luminescence (OSL) calls for a detailed knowledge of the luminescence of feldspars. TL of the various alkali feldspars ((K, Na) Si₃AlO₈) display many common features, and some of these cause great difficulties for dating. After long storage following ionizing irradiation, the TL of most alkali feldspars is known to fade away by “anomalous fading”, which is incompatible with dating. This effect had been attributed to tunnel recombination. Following irradiation, a very intense tunnelling afterglow is observed at temperatures down to liquid nitrogen, in accordance with the observed rate of fading. This emission has a Gaussian spectrum entirely in the infrared (IR) with a maximum at 1.7 eV. It displays an important thermal quenching from 77 to 300 K. Its intensity is related with the ‘disorder’ of the crystal lattice. At higher temperatures, in TL proper, two emission bands can be separated. One is the well-studied complex visible emission, distributed over the spectral region from UV to orange, but mostly ‘blue’. The other is the ‘infrared’ band already observed at lower temperatures, which is attributed to Fe³⁺ ions. These two bands are clearly separated, with the spectral maxima, respectively, below and above 600 nm. They have also different kinetics, the glow peaks temperatures are different. But these two different bands are also coupled in many ways, they have parallel growth and fading. With ‘disordered’ feldspars, the ‘blue’ emission displays anomalous fading, which is stronger than that of the ‘infrared’. The infrared emission is more stable, which may be interesting for the purpose of dating.     

Al纳米颗粒增强微晶硅薄膜太阳电池光吸收的模拟研究

利用价格低廉、性能优良的金属纳米颗粒增强太阳电池的光吸收具有广阔的应用前景. 通过建立三维数值模型, 模拟了微晶硅薄膜电池前表面周期性分布的Al纳米颗粒阵列对电池光吸收的影响, 并对其结构参数进行了优化. 模拟结果表明: 对于球状Al纳米颗粒阵列, 影响电池光吸收的关键参数是周期P与半径R的比值, 或者说是颗粒的表面覆盖度; 当P/R=4–5时, 总的光吸收较参考电池提高可达20%. 与球状颗粒相比, 优化后的半球状Al纳米颗粒阵列可获得更好的陷光效果, 但后者对颗粒半径R的变化较敏感. 另外, 结合电场分布, 对电池光吸收增强的物理机理进行了分析.     

Detailed study of a thermoluminescent mineral exhibiting anomalous fading

Anomalous fading, the unexpected loss of charge carriers responsible for high temperature thermoluminescence, has been shown to affect some minerals that are found in samples proposed for archaeological and geological thermoluminescence (TL) dating studies. This paper describes detailed studies of the phenomenon in one feldspar sample. Three possible explanations are considered and further experiments are proposed to distinguish between them. The implications of anomalous fading for TL dating are assessed and some ways of circumventing its ill-effects are suggested.     

Electron spectroscopy observation of the 1s2s2p(S) state in atomic fluorine by means of electron impact excitation of the hf molecule

The energy of the 1s2s²2p⁶²S) core excited state in atomic fluorine is determined by studying a satellite in the electron beam excited KVV Auger electron spectrum of HF. The satellite is assigned to an atomic autoionization transition 1s2(²2p⁶(²S) → 1ss²2p⁴ (¹D). The energy of the 1s2s²2P⁶(²s) initial state has been determined to be 676.5 eV. Transitions to the 1s²2s²2p⁴³p(³P)and 1s²2s²2P⁴(¹S) states are also observed. The intensity for these transitions is very low.     

Evaluated thermoluminescence trapping parameters–What do they really mean?

The main two trapping parameters in thermoluminescence (TL), the activation energy and the frequency factor, are often calculated and used for the evaluation of the stability of the TL signal at a given temperature. In several cases, “anomalous” values of these parameters, either very high or very low have been reported in the literature. In practically all of these cases, the values reported have been recognized to be effective values which resulted from some special circumstances related to the specific materials in hand. Obviously, these effective values are not associated directly with the real rate of thermal release of carriers from traps at the ambient temperature, prior to heating, and therefore, they do not indicate the real decay time of the TL signal or, in other words, the stability of the signal which may be used in TL dosimetry or dating of archaeological or geological samples. In the present paper, we discuss briefly some of these cases and add, in more detail, a rather elementary situation of very low effective activation energy and frequency factor. A model with two trapping states and one kind of recombination center is used and the simulation includes the numerical solution of the relevant sets of coupled differential equations in the three stages of the measurement, namely, excitation, relaxation and heating for a given set of the trapping parameters. The parameters are chosen in such a way that two overlapping TL peaks occur, which look together like a single first-order peak, but with anomalously low evaluated effective activation energy and frequency factor. Implications regarding the possible results in glow curve deconvolution are discussed.