The chemical etching of fission fragment tracks in natural fluorite

An experimental study of the mechanism for chemical etching of fission fragment tracks in the natural mineral fluorite is described. A systematic search showed that a 3:1 mixture by volume of sulphuric to hydrochloric acids was a most appropriate etchant. Experiments directed at determining the etching efficiency as a function of solvent temperature are also discussed. The preferential track etch ratioVt/Vg, the track length and the track density all depend upon the time and temperature of annealing.

It is variations of the fission track density in fluorite, with etching time and annealing temperature, which make possible an overall geophysical interpretation of annealing data for the mineral in terms of the paleoisotherm of its intrinsic fission track clock.

An interactive image analysis system INTIMAN, assembled for the swift and automatic readout of fission fragment track measurements, in both crystalline and non-crystalline materials, is described. Normal procedures for measuring and analyzing tracks are outlined.     

A study of the basic properties of electrochemical track etching

The basic properties of the electrochemical track etching method proposed by Tommasino were studied for PC and PET foils irradiated with fission fragments and/or alpha-particles. Etching was performed in a specially designed double-wall vessel applying electric fields of different strengths and frequencies. The variation in the diameters of the discharge spots produced around the tracks of fission fragments entering PC and PET foils at right angles was systematically studied as a function of the strength and frequency of the electric field, etching time and etchant temperature. For alpha-tracks registered in PC foils the dependence of the discharge spot diameter on particle energy was also determined. It was found that the production of discharge spots started at a threshold field strength depending on the type of particle. The temperature dependence of the growing rate of discharge spots followed the Arrhenius law, but with a reduced activation energy as compared to that obtained for the chemical etching rate of the bulk material.     

Modeling the fission track etching process in apatite: Segmentation or crystallography influence

In this study, two factors which can influence fission track etching in apatite are considered: track segmentation (induced by thermal annealing) and variable radial etching speed (due to the reagent diffusion during the etching process).

During the latent track annealing, two distinguishable steps can be identified by measuring track lengths or diameters. A length reduction is firstly observed, followed by a segmentation process which leads to the emergence of disrupted regions (gaps).

At present time, electron microscopy studies on fission tracks in apatite show profiles which lead to hypotheses of a variable radial etching speed versus depth. These variations can be interpreted in terms of acid diffusion along the track. Moreover, the existence of several bulk etching speeds related to crystallographic orientation is approached.

Taking into account these different points, a software program, integrating parameters as original track orientation and depth, number of gaps, etc., is developed in order to model the track profile evolution during the etching process. Comparison with experiments in Durango apatite (Mexico) are also undertaken.     

Effects of radiations on the characteristics of alpha and fission tracks in CR-39 detectors

Abstract

The effects of neutron, gamma and alpha radiations on the alpha and fission fragment tracks registration and revelation properties of CR-39 detectors (CR-39 and CR-39(DOP) were studied. It was found that the ratio of the bulk etch rate of irradiated to unirradiated (V_G(irr.)/V_G(unirr.) detectors is linearly dependent on dose. An exponential decrease in fission track densities with increase in neutron fluence was observed. The ratio of V_G(irr.)/V_G(unirr.) was found to be high in CR-39 than that in CR-39(DOP) exposed to the same reactor neutron fluence. The decrease in fission track densities with increase in neutron fluence was observed to be faster in CR-39 than in CR-39(DOP). This indicates that doping with dioctyl phthalate improves the radiation resistance of CR-39 detectors. It was observed that in detectors exposed to an alpha flux of the order of 9.36 × 10⁶ / cm², the fission track density was reduced by 11% and thereafter it remained constant. The results also indicate that thermal neutron fluence up to 7.01 ×10¹¹ neutrons/cm² does not affect the alpha and fission track densities. I.R. spectra were also studied to find out the nature of chemical changes produced by these radiations on CR-39.     

Response of cellulose nitrate track detectors to electron doses

In order to study alternative dose determination methods, the bulk etching velocity and the latent track annealing of LR 115 track detectors was studied during electron irradiation runs from a Pelletron accelerator. For this purpose alpha irradiated and blank detectors were exposed to increasing electron doses from 10.5 to 317.5 kGy. After the irradiation with electrons the detectors were etched under routine conditions, except for the etching time, that was varied for each electron dose in order to reach a fixed residual thickness. The variation of the bulk etching velocity as a function of each one of the electron doses supplied, was interpolated in order to obtain dosimetric response curves. The observed annealing effect on the latent tracks is discussed as a function of the total electron doses supplied and the temperature.     

Diffusion of Na in sodium borate glasses

Diffusion of ²²Na in ion-conducting xNa₂O·(1−x)B₂O₃ glasses (x=0.2 and 0.3) was investigated under standard conditions and under high pressure employing the radiotracer sectioning method. A slight decrease of the diffusion coefficients with increasing time of diffusion annealing is observed and attributed to a structural relaxation of the glass network. The temperature dependence of diffusion was measured below and also in a small temperature range above the glass transition temperature (T_G). Below T_G the diffusion coefficients obey Arrhenius relations. Diffusion in the glass with x=0.3 is fast and associated with an activation enthalpy of 71 kJ mol⁻¹. The diffusion coefficients of the glass with x=0.2 are significantly smaller with an activation enthalpy of 112 kJ mol⁻¹. The activation volume ΔV of Na-diffusion in 0.3Na₂O·0.7B₂O₃ was determined from high pressure diffusion studies at 623 K. A value of 0.52 molar volume of the glass matrix was obtained. According to our knowledge this is the first measurement of an activation volume of diffusion in ion-conducting glasses. The present results will be discussed and compared with dc conductivity data for borate glasses and diffusion results for other oxide glasses reported in the literature.     

Small-angle X-ray scattering from styrene-butadiene-styrene block copolymers

Abstract

A new type of time-dependent and strain-history-dependent viscoelasticity was discovered in semidilute polymer solutions. Dynamic moduli G′ and G″ of 20% and 10% nitrile butadiene rubber (NBR) solutions were recorded as a function of time while oscillatory shear deformations were maintained. The moduli decrease with time was observed only at lower frequencies. The time dependence of G′ was more pronounced than that of G″. At a higher temperature, the time dependence was extended toward higher frequencies also, and the time dependence became stronger. Lowering the concentration of solution gave a similar effect as increasing temperature. After the cessation of oscillations, a slow recovery was observed. The recovery was somewhat faster at the higher temperature. The time-dependent moduli and their recovery were explained by the change and recovery of structures associated with long branches and gels in the NBR. The structure change occurred at higher frequencies also, but it was not observed during the application of oscillation. Only in subsequent measurements at lower frequencies could the structure change be detected. Thus, the change may be regarded as strain history dependent. The mechanism of the structural change was explained with either the entanglement or osmotic pressure models, depending on concentration.     

Modelling the length distribution of etched tracks taking into account fragmentation due to partial annealing

Fission track length measurements on apatite minerals are of great interest in thermo-chronology studies. RBS analyses on Durango apatites irradiated by Krypton ions have previously shown the progressive fragmentation of tracks by annealing. This study made for different irradiation energies corresponding to those of uranium fission fragments has been completed by TEM and AFM on etched tracks. In all cases, segmentation figures have been observed, that clearly necessitates to introduce fragmentation of latent tracks to model the length distribution of uranium etched fission tracks. This presentation concerns the case of a homogeneous population of tracks with partial amorphization. The next step will consist in considering multiple sub-populations with different segmentation rates. This algorithm is a new aspect to be included in our model, which already takes into account diffusion and crystallography in the track etching process.     

页岩气中CH4-C2H6吸附-扩散分子动力学研究

本文采用巨正则蒙特卡洛(GCMC)和分子动力学(MD)模拟方法,对比分析了不同温度、压力和孔径对二元气体(CH4-C2H6)在K-伊利石中的吸附-扩散的影响.结果表明,在低压条件下,K-伊利石对C2H6的吸附能力大于CH4, C2H6优先吸附在K-伊利石孔隙表面.热力学因子随着孔径的增加而减小,C2H6的热力学因子大于...     

Effect of uniaxial stress on the dielectric properties of BaTiO3+0.1wt.%Eu2O3 ceramics

ABSTRACT

BaTiO₃+0.1wt.%Eu₂O₃ ceramics were prepared by a solid-state reaction method. The dielectric behavior of these ceramics as a function of uniaxial pressure has been systematically studied. The external stress showed obvious effects on these properties. An increase of the Curie point (T_c) and decrease of the Curie–Weiss temperature (T₀) was observed with increasing pressure, resulting in an increase in the first-order nature of the phase transformation (T_c–T₀ increases). Broadening and flattening of the permittivity versus temperature curves near their maximum was found. The pressure behavior of thermal hysteresis and the ??/?T vs. T plot suggests that the phase transition changes to second-order type with increasing pressure. Furthermore, the Curie–Weiss constant obtained from a modified Curie–Weiss law strongly decreases with increasing pressure, suggesting that the mechanism of phase transition is going to order–disorder type.     

Influence of hydrostatic pressure on the diffusion of hydrogen in n-GaAs : Si

Hydrogen diffusion experiments have been performed in buried silicon doped GaAs epilayers under hydrostatic pressure. The deuterium diffusion profile in n-GaAs : Si depends on the hydrostatic pressure: a plateau followed by a steep decrease progressively appears as the pressure is increased. This has been interpreted as being due to the increasing importance of the trapping-detrapping process of H⁻ on Si⁺ donors during the hydrogen diffusion. This increase has been attributed to a deepening of the hydrogen acceptor level with respect to the bottom of the Γ conduction band of GaAs as the hydrostatic pressure increases.     

高压热处理对铝青铜热物理性能的影响

在5 GPa压力下对铝青铜进行750℃、保温15 min的高压热处理,对高压热处理前后铝青铜的电导率以及25～600℃温度范围内的热扩散系数、热容和热导率进行测试,结合显微组织的观察结果,探讨了高压热处理对铝青铜热物理性能的影响。研究表明:高压热处理能增大铝青铜的热扩散系数,减小热容;对热导率而言,温度低于400℃时高压热处理能增大铝青铜的热导率,而温度高于400℃时高压热处理能减小铝青铜的热导率。分析认为,产生变化的主要原因是高压热处理使铝青铜的微观组织发生了变化。     

Observations of fission-tracks in zircons by atomic force microscope

The fission-track (FT) method is a dating technique based on the observation of damage (tracks) by spontaneous fission of ²³⁸U left in a mineral. The date is calculated from the track density and the uranium concentration in the mineral. This is possible because the number of tracks is a function of uranium concentration and time since the start of track accumulation. Usually, the number of tracks is counted under an optical microscope after etching (chemical expansion of a track). However, as FT density per unit area rises, it becomes difficult to count the number of tracks. This is due to the fact that FTs overlap one another and are unable to be readily distinguished. This research examines the potential of atomic force microscope (AFM) for FT dating using zircons, which are likely to show higher FT density than other minerals due to their high U concentrations.To obtain an AFM image for a sample prepared for FT dating, removing the static electricity of the sample is essential to avoid an unexpected movement of the cantilever. A grain should be wider than about 30 μm to bring the cantilever on the mineral surface. Polishing with a fine grained compound is very important. There is not much difference in sharpness between images by AC mode (scanning with vibrating cantilever at a constant cycle) and Contact mode (scanning with the cantilever always in close contact with the surface). To confirm how tracks can be identified with the AFM, an AFM image was compared with an image obtained with the optical microscope. When change in the number of tracks and their shapes were observed through stepwise etching, the track expanded as the etching time increased. In addition, the etching rate was slower for large tracks than those for small tracks. This implied that the AFM can be used to observe etching of zircons with different degrees of nuclear fission damage. A track that could not be seen with the optical microscope due to insufficient etching could be observed by AFM methods, indicating the possibility of FT dating with high track densities using AFM after relatively short etching periods.     

Diffusion of deuterium in tantalum from internal friction measurements (Gorsky effect)

The long-range diffusion of deuterium in tantalum has been investigated as a function of temperature by means of the anelastic process due to redistribution of deuterium impurities between compressed and dilated regions of the sample, under an applied stress alternating at about 4 Hz. The diffusion coefficient was found to obey an Arrhenius-type law in the temperature range 200–390 K; a deviation was observed at lower temperatures. The diffusion parameters in the exponential region areD _0D=(3.3±1.5)×10⁻⁴ cm²/s, andW _D=(0.176±0.008) eV.     

Polarization behavior of Ni-YSZ cermet anodes in YSZ fuel cells running on methane under internal reforming conditions

The polarization characteristics of the Ni-YSZ cermet anode/YSZ interface were studied as a function of gas phase composition, temperature and anodic overpotential in methane fuelled internal reforming YSZ fuel cells. AC impedance measurements carried out under open circuit conditions in the temperature range 800 to 900°C showed the presence of at least two rate-limiting processes that were influenced by temperature and gas phase composition. The apparent polarization resistance, R_app, of the Ni-YSZ cermet anode/YSZ interface was found to increase with increasing methane partial pressure and decreasing H₂O partial pressure. The activation energy related to the apparent polarization conductance R _app ⁻¹ varied between 0.7 and 1.1 eV, mainly due to the variation of P_{H 2 O}. The order of magnitude of the apparent capacitance, C_app, values calculated from AC impedance data under open circuit conditions indicate that the observed capacitance corresponds to the double layer capacitance of the Ni/YSZ interface and/or a pseudo-capacitance related to adsorption of species on the Ni-YSZ cermet electrode accompanied by charge transfer. C_app was found to decrease with increasing methane partial pressure. AC impedance measurements carried out under closed circuit conditions at 900 °C and four different P_{H 2 O} showed the appearance of a low-frequency inductive loop at high anodic over-potentials, in addition to the features observed under open circuit conditions. The effect of gas phase composition on R_app was similar to the one observed under open circuit conditions. In addition an almost exponential decrease of R_app with increasing anodic overpotential was observed. The present results are compared with results presented in literature and discussed in the frame of the mechanism of the electrochemical and catalytic reactions taking place over the anode. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Diffusion-controlled transformation plasticity of steel under externally applied stress

The transformation plasticity of steel during phase transformation under external stress was modelled on a migrating interface diffusion mechanism. Atomic diffusion along the migrating phase interface is assumed to cause transformation plasticity by an accelerated Coble creep. A creep equation on transformation plasticity is derived as a function of transformation rate, temperature and externally applied stress. Predictions are compared with dilatometric measurements during the austenite-to-ferrite and ferrite-to-austenite transformation of steel under various levels of uniaxial compressive stress. Good agreement was found between the calculated and experimental transformation strain. The model proposed also successfully describes the thermally activated behaviour of the transformation strain. The evaluated effective diffusion coefficients on the migrating interface are three to four orders of magnitude larger than those reported for stationary boundaries.     

高气压空气环状感性耦合等离子体实验研究和参数诊断

等离子体的电子密度分布, 电子碰撞频率分布, 覆盖面积, 厚度是影响其覆盖目标电磁散射特征的关键属性. 对此, 本文开展了在20 cm×20 cm×7 cm石英腔内感性耦合等离子体(ICP)的放电实验, 观察了在高气压条件下, 空气ICP的环形放电形态, E-H模式跳变现象和分层结构, 测量了其电负性核心区和电正性边缘区宽度和厚度随功率、气压的变化趋势, 并通过COMSOL Multiphysics对平板线圈磁场强度分布的分析和电负性气体扩散理论给予上述现象合理的解释, 同时, 利用微波透射干涉法测量了核心区域的电子密度随功率和气压的变化曲线, 利用理论模型计算了边缘区域的电子密度分布, 最后通过辅助气体Ar发射谱线的玻尔兹曼图形法得到了核心区和边缘区的电子激发温度.     

Recoil studies of fission products formed in the fission of U by protons of energies 25–85 MeV

The recoil properties of ten fission products with masses ranging from 72 to 136 formed in the fission of ²³⁸U with protons of energies 25–85 MeV have been determined radiochemically by the integral-range method. From the recoil properties of the products and the Monte Carlo cascade calculations the average kinetic energy, cascade deposition energy, and anisotropy parameter for each fission product has been calculated. The kinetic energy and the excitation energy of the primary fragments leading to the observed fission product, and the total kinetic energy and the total excitation energy of the primary fragment pair have also been calculated.

The results indicate that up to a bombarding energy of 40 MeV fission takes place predominantly by the compound nucleus mechanism, with an increasing contribution of the direct interaction mechanism as the bombarding energy increases. The kinetic energy deficit was found to decrease with increasing bombarding energy. The fission products formed from the symmetric mode of fission have a larger separation distance between the charge centres of their respective primary fragments than those for the asymmetric mode of fission.     

Proton dose-dependent modification in track etching response in some polymers

In the present work, the effect of four different doses of 62 MeV protons, on the fission fragment track etching characteristics of two polymers, viz. polycarbonate (Makrofol-N (MFN)) and polyimide (PI) are studied by nuclear track technique. The bulk etch-rate of PI increased by around 30% at the highest proton dose, whereas the activation energy of etching remained almost constant for the same. A considerable increase in the bulk etch-rate of MFN was observed (75%) at the highest proton dose. The activation energy of etching of the fission fragment tracks in MFN was also found to be an inverse function of dose.     

Cu互连应力迁移温度特性研究

提出了一种基于扩散-蠕变机制的空洞生长模型, 结合应力模拟计算和聚焦离子束分析技术研究了Cu互连应力诱生空洞失效现象, 探讨了应力诱生空洞的形成机制并分析了空洞生长速率与温度、应力梯度和扩散路径的关系. 研究结果表明, 在Cu M1互连顶端通孔拐角底部处应力和应力梯度达到极大值并观察到空洞出现. 应力梯度是决定空洞成核位置及空洞生长速率的关键因素. 应力迁移是空位在应力梯度作用下沿主导扩散路径进行的空位积聚与成核现象, 应力梯度的作用与扩散作用随温度变化方向相反, 并存在一个中值温度使得应力诱生空洞速率达到极大值. 关键词： Cu互连 应力迁移 应力诱生空洞 失效