Characterization of x‐rays emerging from between reflector and sample carrier in reflector‐assisted TXRF analysis

The possible application of an Si reflector, which is placed just above the sample carrier in total reflection x‐ray fluorescence (TXRF) analysis, was investigated. The x‐rays that were emitted from an Mo tube and passed between the Si reflector and the Si sample carrier were analyzed with an Si drift detector. In our experimental setup, the angle between the reflector and the sample carrier can be changed by adjusting the inclination of the reflector. The intensity of the x‐rays that emerged from between the two Si surfaces drastically changed depending on the reflector angle. At a proper reflector angle, this intensity showed a maximum and, in addition, the Compton peak in the x‐ray spectrum was suppressed. When this x‐ray beam was used for excitation of TXRF signals, the highest intensity of x‐ray fluorescence emitted from the sample was detected, indicating that these experimental conditions are useful for the enhancement of TXRF intensities. Copyright © 2004 John Wiley & Sons, Ltd.     

On the dependence of the free carrier concentration on light intensity in photorefractive crystals

The dependence of the free charge carrier concentration on light intensity is analyzed in two types of crystals where photorefractive centers are either traps or donors. Conditions under which the dependence becomes sublinear at relatively low light intensities are established.     

Multibubble sonoluminescence intensity dependence on liquid temperature at different ultrasound intensities.

It is shown that the influence of liquid temperature on the sonoluminescence (SL) intensity is different depending on the ultrasound intensity. At the ultrasound intensities not much higher than the cavitation appearance threshold the SL intensity increases with the temperature. At the ultrasound intensities considerably exceeding the cavitation threshold the SL intensity decreases with an increase of the temperature. At intermediate ultrasound intensities the SL intensity temperature dependence is extreme: the cavitation activity at first increases with temperature, reaches a maximum and then decreases. Continuous and pulsed modes of irradiation at frequencies 880 and 21.9 kHz were used in experiments.     

Speciation of selected metals in aerosol samples by TXRF after sequential leaching

Total reflection x‐ray fluorescence (TXRF) spectrometry was applied after sequential leaching for the speciation of selected elements in particulate matter, in order to complete the knowledge of the mobility of the selected elements and to determine which components are harmful to works of art. Samples were collected on filters in two churches, one situated in a rural area and the other in an urban area. A five‐stage sequential leaching scheme for the speciation of K, Ca, Fe, Zn and Pb was applied, the fractions obtained being as follows: exchangeable elements; elements bound to carbonates; elements bound to Fe and Mn oxides; elements bound to organic matter; and the digested insoluble residue. It was found that, in the case of the church in the urban area, much of the K, Fe and Zn appeared as mobile elements, whereas for the church situated in the rural area, the amounts of Ca and Fe were most mobile. Copyright © 2006 John Wiley & Sons, Ltd.     

Determination of halogen levels in marine geological samples

ABSTRACT

A method for determining levels of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) in marine geological samples using wavelength dispersive X-ray fluorescence is presented here. Samples are prepared as pressed powder pellets. The method makes full use of the advantages of the ability of the modern X-ray fluorescence spectrometer to detect ultra-light elements and high-powered X-rays. A series of calibration standards with an appropriate concentration range was developed using a standard addition method. Empirical coefficients were used to correct for matrix effects in the case of F and Cl, the rhodium Kα -Compton peak was used as internal standard for Br matrix corrections, and the rhodium Kb-Compton peak was used to correct for the matrix effect on I. For % concentration of the analyte, the precision (relative standard deviation) of the method was <5%. For concentrations <0.1%, the relative standard deviation depended heavily on the count rates (or concentration). The accuracy of the method was validated by comparison of the results to similar reference materials. The detection levels of this method (counting time100 s) were 100, 5, 0.5, and 10 µg g^?1 for F, Cl, Br, and I, respectively. The method was here used to determine the levels of halogens in samples of 19 marine sediments (China, Russia, Canada, American), 10 marine manganese nodules (China, Russia, American, Germany, India, Japan), 4 cobalt-rich crust reference materials (Russia, China), reference materials, and 3 phosphorites.     

Temperature dependence of the calibration factor of radon and radium determination in water samples by SSNTD

The sensitivity of a ²²⁶Ra determination method of water samples by SSNTD was measured as a function of storage temperature during exposure. The method is based on an etched track type radon monitor, which is closed into a gas permeable foil and is immersed in the water sample. The sample is sealed in a glass vessel and stored for an exposure time of 10–30 days. The sensitivity increased more than a factor of two when the storage temperature was raised from 2 °C to 30 °C. Temperature dependence of the partition coefficient of radon between water and air provides explanation for this dependence. For practical radio-analytical application the temperature dependence of the calibration factor is given by fitting the sensitivity data obtained by measuring ²²⁶Ra standard solutions (in the activity concentration range of 0.1–48.5 kBq m⁻³) at different storage temperatures.     

A different approach in sample preparation method for metallic contamination study by ToF-SIMS and TXRF

We propose a methodology to realize reliable reference samples for ToF-SIMS quantitative analysis of metallic contaminants. The procedure consists of spinning a Co contaminated solution, for which the contaminant concentration has been previously determined by ICP-MS, on a clean Si-wafer with a thin surface oxide obtained by SC1 treatment. We have compared the ToF-SIMS results with TXRF and we have demonstrated the validity of the procedure. We have also evidenced the effects of sample aging on the measurements showing that contaminant migration towards the interface between oxide and silicon can significantly impact on the quantification correctness.     

Charge carrier concentration in glasses. dependence on composition

Admittance spectra of the ion conducting glasses xNa₂O(1−x)SiO₂ and xK₂O(1−x)SiO₂,(x=0,1–0,3) have been studied on small signal conditions from room temperature to 713 K. Conductivity relaxation in the bulk and space charge relaxation due to drift and diffusion near the electrodes were found in separated parts of the frequency range 10⁻⁴–10⁶ Hz. The data show Arrhenius behaviour for dc conductivity and conductivity relaxation. The determination of the charge carrier concentration is based on the analysis of the beginning of space charge relaxation. The free carrier concentration, n₀, were evaluated to be of the order of 10²³ m⁻³ at temperatures 400 – 700 K and show a weak dependence on composition. The dominant factor determining conductivity was mobility in these glasses. The strong temperature dependence of n₀ below 400 K indicates changed conditions for the development of the space charge relaxation which are discussed. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994.     

Space and wavelength dependence of speckle intensity

A unified, analysis is presented for the spatial and the spectral sensitivity of speckle (the rapid spatial variations which occur in an image when illumination of narrow spectral width is used) in a space-invariant linear system. In prior work considering speckle size, others have shown that its spatial variation is functionally dependent primarily on the autocorrelation function of the system's impulse response, but effects of varying the wavelength were largely ignored. In the present paper we treat the general problem in which a diffuse object, illuminated by a collimated, monochromatic beam, is imaged by a system whose amplitude impulse response isz(x, η), wherex and η are space and normalized (temporal) frequency coordinates, respectively. An expression is derived for the multidimensional autocorrelation functionR _u (Δx,η ₁,η ₂) of the intensityu(x,η) in the image plane. Functionally, it depends upon a convolution of the system autocorrelation functionR _u (Δx,η ₁,η ₂) with the characteristic function of the distribution function for heights, which is used to model the input object's surface. Examples are presented; and, it is shown that one can infer valuable information about the variation of heights for points on the surface of the input diffuse object, which are separated by much less than the classical resolution limit.     

Charging and rotational dependence of line position

For a charged sample the measured binding energies depend on the location of the sample within the sample chamber^{1, 2}. If it is only the angle between the sample surface and the analyser which is varied then the line position depends, in a characteristic way, on the rotation angle. This dependence can be used to prove whether or not a sample is charged. In addition, the amount of rotational dependence of line positions gives an indication of the magnitude of charging.     

Time and field dependence of excess carrier concentration in semiconductors

The time and space distribution of excess carriers in semiconductor devices is derived through the solution of the ambipolar continuity equation. Both build-up of excess carriers due to external excitation and their decay following its termination are presented. A detailed solution for a 1-D photoconductive device with various boundary conditions is obtained. The solution is expanded to the 3-D distribution, where an analytical solution is given for the diffusion region of photodiodes. The procedure for solving the 3-D problem in photoconductor devices is outlined. The derived equations are used to demonstrate the advantages of the “covered electrodes” structure and in order to obtain an accurate value for the ambipolar mobility as measured in a four-probe device.     

Temperature dependence of mobilities and carrier concentrations in semi-insulating GaAs

The temperature behavior of electron and hole mobilities and carrier concentrations was measured in p-type Cr doped semi-insulating GaAs. The above quantities were determined by measuring at a given temperature the photomagnetoresistance and photo-Hall effect vs magnetic field intensity. A minimum of hole concentration is observed at 210–225 K. The electron concentration either remains constant below 190–200 K or it rises again at lower temperatures. The mobilities of both carriers show a maximum at almost the same temperatures with those where the behavior of n and p changes. We try to explain the above on the basis of radiative recombination and impurity conduction.     

Shubnikov-de Haas effect and effective mass inn-InP in dependence on carrier concentration

Shubnikov-de Haas investigations onn-InP are presented and the effective mass as a function of carrier concentration is determined. The experiments are carried out with bulk and liquid phase epitactically grown material and carrier concentrations betweenn=10¹⁷ and 10¹⁹cm^–3. Temperatures employed ranged fromT=2 to 77 K and magnetic fields were applied up toB=22 T. Supplementing Kane's theory by introducing both temperature and electron concentration dependence, the nonparabolicity of the effective mass for temperatures betweenT=0 K and 300 K is calculated. The result fits quite well to the experimental results.Dedicated to Prof. Dr. Günter Lautz on the occasion of his 70th birthday     

The dependence of muon intensity on the geomagnetic latitude

The vertical momentum spectrum of cosmic-ray muons has been determined by a counter controlled neon-hodoscope in the spectral region (0.2–3) Bev/c at geomagnetic latitude 12 °N. The observed spectrum agrees satisfactorily with the calculated spectrum of Olbert for muon momentum above 1.8 Bev/c. Below about 1.8 Bev/c, the measured spectrum exceeds slightly the theoretical spectrum of Olbert, calculated for the same geomagnetic latitude. The measured spectrum agrees with the experimental spectrum of Allkofer at 9 °N, but is somewhat below the spectrum obtained by Hayman in the low momentum region at 57.5 °N. This shows that there exists a latitude dependence of the low momentum muon spectrum. The estimated integral intensity of muon of momentum ≧320 Mev/c is found to be 7.3×10^?3 cm^?2 sec^?1 str^?1 which agrees with the value of other investigators^1–9.     

Microfluidic sample preparation for elemental analysis in liquid samples using micro X‐ray fluorescence spectrometry

The integration of microfluidic devices with micro X‐ray fluorescence (micro‐XRF) spectrometry offers a new approach for the direct characterization of liquid materials. A sample presentation method based on use of small volumes (<5 µl) of liquid contained in an XRF‐compatible device has been developed. In this feasibility study, a prototype chip was constructed, and its suitability for XRF analysis of liquids was evaluated, along with that of a commercially produced microfluidic device. Each of the chips had an analytical chamber which contained approximately 1 µl of sample when the device was filled using a pipette. The performance of the chips was assessed using micro‐XRF and high resolution monochromatic wavelength dispersive X‐ray fluorescence, a method that provides highly selective and sensitive detection of actinides. The intended application of the device developed in this study is for measurement of Pu in spent nuclear fuel. Aqueous solutions and a synthetic spent fuel matrix were used to evaluate the devices. Sr, which has its Kα line energy close to the Pu Lα line at 14.2 keV, was utilized as a surrogate for Pu because of reduced handling risks. Between and within chip repeatability were studied, along with linearity of response and accuracy. The limit of detection for Sr determination in the chip is estimated at 5 ng/µl (ppm). This work demonstrates the applicability of microfluidic sample preparation to liquid characterization by XRF, and provides a basis for further development of this approach for elemental analysis within a range of sample types. Copyright © 2014 John Wiley & Sons, Ltd.     

Optical determination of carrier mobility in GaAs

We analyze the radiative recombination of free electrons to acceptor-bond holes in GaAs at helium temperatures and obtain the energy distribution of conduction-band electrons in applied weak electric fields. We are able to determine electron temperatures, drift momenta, and mobilities as functions of field. Direct experimental proof is given for mobility enhancement through screening by a free-carrier plasma.     

A new type of sample tube for reducing convection effects in PGSE-NMR measurements of self-diffusion coefficients of liquid samples

Pulsed gradient spin-echo (PGSE) NMR measurements of the self-diffusion coefficients of low viscosity liquids are greatly hampered by the effects of convection especially away from ambient temperature. Here we report on a new NMR tube designed to minimize the deleterious effects of convection. In this tube, which derives from a Shigemi symmetrical NMR tube, the sample is contained in an annulus formed from a concentric cylinder of susceptibility matched glass. The performance of this tube was demonstrated by conducting measurements on the electrochemically important LiN(SO3CF3)2 (LiTFSI)-diglyme (DG) system. Calibrations were first made using DG at column heights of 2, 3, and 4-mm in the temperature range between -40 and 100 degrees C. Measurements of the diffusion coefficients of the lithium, anion, and DG were then performed to probe the solvent-ion and ion-ion interactions in the DG doped with LiTFSI. Changes in the 1H, 7Li, and 19F PGSE-NMR attenuation curves at -40 degrees C provided clear evidence of interactions between the DG and lithium ion.