Effect of mineral composition on thermoluminescence detection of irradiated seafood

Data from import control of irradiated seafood were collected from 300 batches of seafood. Thermoluminescence (TL) analysis of the seafood, based on measurement of thermoluminescent minerals separated from intestinal tract, was carried out with a Risø TL-DA-10 instrument. As identified by X-ray diffraction and SEM/EDS analysis, four main categories of minerals were extracted: tectosilicates, phyllosilicates, carbonates and sulphates. Detection of irradiation was reliable when based on the TL of tectosilicate minerals, i.e. quartz and feldspar. Suitable minerals were found in most seafood: only about five percent of all samples could not be successfully analysed because no minerals or only non-thermoluminescent clays or carbonates were found. False positive results were never obtained. A false negative decision results if analyses are based on hydrous clays or carbonates in the form of aragonite.     

Two-stage thermal stimulation of thermoluminescence

A thermoluminescence (TL) model of two-stage stimulation of electrons into the conduction band is discussed. This release of the carriers is assumed to take place via an intermediate localized excited state. Electrons are thermally stimulated from the trap into an excited state and then thermally released into the conduction band from which they may either be retrapped or recombine with holes in centers. The model resembles the previous “semi localized” model, but we concentrate only on recombination of electrons that go through the conduction band. It also bears similarity to the effect of thermally-assisted optically stimulated luminescence (OSL) previously discussed in the literature.The model is studied by solving the set of the relevant four simultaneous differential equations which govern the process during heating or isothermal decay. Using different sets of parameters, we can get pseudo-first-order, pseudo-second-order as well as intermediate cases, which are identified by their symmetry coefficient. Once the effective order is established, different analytical methods are used to determine the effective activation energy and frequency factor. We used the peak-shape methods, the various heating rate (VHR) method and the method based on the change of phosphorescence decay with temperature. The results are compared to the parameters used in the simulation. In many cases, the effective activation energy is equal to E₁ + E₂ where E₁ and E₂ are, respectively, the activation energies for the first and second stage of thermal stimulation. The numerical simulation results are accompanied by an analytical treatment using the usual quasi-steady assumption. Unusual cases, in which the effective frequency factor and the effective retrapping probability coefficient are temperature dependent, are identified. Some cases in which the effective activation energy is close to E₁ rather than E₁ + E₂ are identified and discussed. The relevance of this possible situation to the evaluation of the stability of TL signals is also considered, and a possible effect of anomalous stability is predicted.     

Dynamo quenching due to shear flow

We provide a theory of dynamo (alpha effect) and momentum transport in three-dimensional magnetohydrodynamics. For the first time, we show that the alpha effect is reduced by the shear even in the absence of magnetic field. The alpha effect is further suppressed by magnetic fields well below equipartition (with the large-scale flow) with different scalings depending on the relative strength of shear and magnetic field. The turbulent viscosity is also found to be significantly reduced by shear and magnetic fields, with positive value. These results suggest a crucial effect of shear and magnetic field on dynamo quenching and momentum transport reduction, with important implications for laboratory and astrophysical plasmas, in particular, for the dynamics of the Sun.     

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.     

Effect of plastic deformation and quenching on the absolute thermal emf of nickel

The effect of the degree and rate of plastic deformation of nickel on the change of its absolute thermal emf was studied. The dynamic effect of the change of thermal emf was established, the dynamic coefficient being 1.22–1.25. Plastic deformation of quenched nickel reduced its absolute thermal emf, on the basis of which conclusions are drawn about the contributions, different in sign, of holes and dislocations to the change of the absolute thermal emf of nickel. The kinetics were studied of the recovery of the thermal emf induced in nickel by plastic deformation, and the existence was established of two stages of recovery, differing in nature and with different activation energies, 0.1 and 0.3 eV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 77–81, June, 1971.     

Evaluation of parameters from thermal desorption spectra – methods borrowed from the analysis of thermoluminescence

A number of methods for extracting the activation energy, pre-exponential factor and reaction order associated with the Polanyi–Wigner rate formulation have been reported in the literature. An entirely analogous equation had been utilized in the study of thermoluminescence (TL) and several methods have been developed for the extraction of the relevant parameters. Some of these methods are practically identical to those developed for the study of thermal desorption, whereas others have not been developed for thermal desorption but can be used with only very minor adjustment to the analysis of thermal desorption curves. In the present work, the utilization of the methods developed for the analysis of TL for the study of thermal desorption data is advocated.     

Effect of gamma irradiation on thermoluminescence and thermodynamic parameters of LiKSO4 doped with Nd2 O3

Abstract

The thermoluminescence and thermo-dynamic parameters of LiKSO₄: Nd were investigated. The effect of Nd dopant concentration in the range 0.1-1% as well as that of γ-irradiation dose in the range 56.3-3.24 × 10⁵ Gy were studied. The glow curves of the material are characterized by a double peak; each behaving seperately with radiation dose. The highest TL enhancement was obtained for Nd concentration of 0.5%; while irradiation dose of few hundreds Gy gave the best TL response. The thermodynamic parameters of LiKSO₄ doped with 0.5% Nd decreased with radiation dose up to about 5000 Gy.     

Lattice thermal conductivity due to impurities

Phonon conductivity of NaF has been calculated using non-linear theory of heat transfer in solid given by Kazakov and Nagaev and shows good agreement with the measurements of Jackson and Walker in the temperature range 2–10°K.     

Lattice contraction due to quenching in vacancies in platinum and gold

Combined measurements of lattice parameter and electrical resistivity change of platinum and gold after quenching were performed. The lattice contraction due to vacancies could be determined.     

Luminescence quenching of F centers due to nonradiative de-excitation during lattice relaxation

F centers have no luminescence in some crystals. This occurs only in cases intermediate between the adiabatic and the nonadiabatic limits, when we adopt a reasonable damping rate of the configuration coordinate whose oscillation is triggered by photon excitation at an energy E. When $\text{(}\text{EE}{}_1\text{)}\text{E}{}_1\text{> 1 ? 4Λ}$, with E₁  absorption-peak energy, the luminescence quantum efficiency decreases steeply. Here Λ  S/E₁ represents Bartram and Stoneham's parameter with S  lattice-relaxation energy. Otherwise, the nonradiative de-excitation requires a thermal activation, but the activation energy is much smaller than that required at thermal equilibrium.     

不同参数对室内传输通道热晕效应影响的数值分析

着重讨论了不同参数对室内传输通道热晕效应的影响。数值计算的结果表明：对于理想光束,即使在10 kW的激光功率情况下,传输距离大于25 m,吸收系数大于0.013 km-1时,就需要考虑室内传输通道热晕效应对光束质量的影响。随着吸收系数的增大,传输距离的加长,激光功率的提高,通道内热晕效应的影响越来越严重,应采取一定的措施来减小室内传输通道热晕效应。     

不同参数对室内传输通道热晕效应影响的数值分析

着重讨论了不同参数对室内传输通道热晕效应的影响。数值计算的结果表明:对于理想光束,即使在10 kW的激光功率情况下,传输距离大于25 m,吸收系数大于0.013 km-1时,就需要考虑室内传输通道热晕效应对光束质量的影响。随着吸收系数的增大,传输距离的加长,激光功率的提高,通道内热晕效应的影响越来越严重,应采取一定的措施来减小室内传输通道热晕效应。     

Macroscopic thermal entanglement due to radiation pressure

Can entanglement and the quantum behavior in physical systems survive at arbitrary high temperatures? In this Letter we show that this is the case for a electromagnetic field mode in an optical cavity with a movable mirror in a thermal state. We also identify two different dynamical regimes of generation of entanglement separated by a critical coupling strength.     

Vibrations of polygonal plates due to thermal shock

Vibrations of polygonal elastic plates due to thermal shock are investigated through use of complex variable theory. The numerical results are shown graphically for different polygonal plates and results for triangular, square and circular plates are compared with published results.     

Determination of thermoluminescence kinetic parameters of thulium doped lithium calcium borate

For the first time kinetic parameters of thulium doped Lithium calcium borate (LCB) Thermoluminescence (TL) material are reported here. Irradiated LCB:Tm³⁺ powder has revealed two intense TL glow peaks one at 510 (peak 1) and the other at 660 K (peak 2). Activation energy (E), frequency factor (s) and order of kinetics (b) of these peaks were determined by various heating rate (VHR), initial rise (IR), and peak shape (PS) methods. The trap depth and frequency factor determined for peaks 1 and 2 of LCB:Tm phosphor using VHR and IR methods are in good agreement. The average activation energy of peaks 1 and 2 obtained by these methods is 1.62 and 1.91 eV respectively. The frequency factors of peaks 1 and 2 are in the range of 10^13–16 and 10^12–14 sec⁻¹ respectively. The E and s values estimated using the glow peak shape dependent parameters are relatively less compared to the values obtained from other methods. The large difference in these values is due to the complex nature of the glow curves. The order of the kinetics process for complex glow curve peaks could not be assigned on the basis of shape parameters alone but T_m response on absorbed dose is to be considered for final confirmation. Glow peaks 1 and 2 of LCB:Tm³⁺ obey first and general order kinetics respectively.     

Effect of thermal annealing on light yield,low temperature thermoluminescence,and time profiles of LuAG:Pr scintillator crystals

Measurements of light yield, low temperature thermoluminescence, and scintillation time profiles, performed comparatively on “as grown” and thermally annealed LuAG:Pr samples, are reported. It is shown that traps play an efficient role in the scintillation of LuAG:Pr, being responsible for the yield decrease and introducing a long component to the time profiles. The trap concentrations in the annealed crystals are lower than in the non-annealed ones, which correlates with the yield enhancement.     

Lattice thermal resistivity due to the core dislocations

The lattice thermal resistivity of an insulator having core dislocations has been studied by obtaining an analytical expression for it. The lattice thermal conductivity of a sample has also been calculated for different values of the core dislocation scattering strength to see the effect of core dislocation on it.