Characteristic Kα X-rays Research Articles

Target heating in femtosecond laser–plasma interactions: Quantitative analysis of experimental data

We study electron heating and stopping power in warm dense matter as formed in interactions of sub-picosecond high-intensity lasers with solid bulk targets. In such interactions, an intense beam of forward moving relativistic electrons is created, inducing a compensating return current and generating characteristic Kα x-ray radiation along the propagation path. The theoretical calculations presented here are inspired by, and tested against, a previously published study that provides bulk-temperature and absolutely calibrated Kα radial profiles. By using Monte Carlo simulations, the experimental data allow for inferring the flux of the relativistic electrons, which is a crucial input for the target heating calculations. For the latter, a “rigid beam” model is employed, describing the central, nearly homogeneous, part of the target. The comparison with the experiment shows a fairly good agreement. For the conditions analyzed, we find that the effect of the return current is dominant both in the target heating and in the beam stopping.

Refinement of the Compton–Rayleigh scatter ratio method for use on the Mars Science Laboratory alpha particle X-ray spectrometer: II – Extraction of invisible element content

The intensity ratio C/R between Compton and Rayleigh scatter peaks of the exciting Pu L X-rays in the alpha particle X-ray spectrometer (APXS) is strongly affected by the presence of very light elements such as oxygen which cannot be detected directly by the APXS. C/R values are determined along with element concentrations by fitting APXS spectra of geochemical reference materials (GRMs) with the GUAPX code. A quantity K is defined as the ratio between the C/R value determined by Monte Carlo simulation based on the measured element concentrations and the fitted C/R value from the spectrum. To ensure optimally accurate K values, the choice of appropriate GRMs is explored in detail, with attention paid to Rb and Sr, whose characteristic Kα X-ray peaks overlap the Pu Lα scatter peaks. The resulting relationship between the ratio K and the overall oxygen fraction is linear. This provides a calibration from which the concentration of additional light invisible constituents (ALICs) such as water may be estimated in unknown rock and conglomerate samples. Several GRMs are used as ‘unknowns’ in order to evaluate the accuracy of ALIC concentrations derived in this manner.

Study of strain propagation in laser irradiated silicon crystal by time-resolved diffraction of K-α x-ray probe of different photon energies

An experimental study on the time resolved x-ray diffraction from laser shocked silicon crystal, carried out using a 10 TW Ti:sapphire laser system, is presented. The characteristic Kα x-ray line radiation generated by 45 fs laser produced plasmas of two different target materials (iron and copper) is used as the probe, whereas the stretched pulse of sub-nanosecond duration (pump), derived from the same laser, is used to compress the sample. The use of x-ray probe of different photon energies yields information about the strain over a greater crystal depth. The dynamics of the strain propagation is inferred by monitoring the evolution of rocking curve width of the shocked sample at different time delays between the pump and the probe pulse. The shock velocity deduced from these measurements is ∼106 cm/s, consistent with the sound velocity in bulk silicon. The maximum elastic compression observed is 0.4%, indicating a pressure of 0.8 GPa.

Multi-phase Characterization of Asphalt Concrete Using X-ray Microfluorescence

The objective of this study was to develop a microstructure characterization technique to capture the multi-phase nature of asphalt concrete using x-ray microfluorescence. This study examines the morphology and positions of aggregates, sand mastic and air void phases of asphalt concrete. Three different samples with targeted air void levels of 4%, 7%, and 10% were analyzed using an X-ray microscope. The cylindrical asphalt specimens were cut into slabs and then polished, and finally white zinc-oxide powder was pressed into the voids. The zinc-oxide powder helped to discern air voids from aggregate and mastic. After sample preparation, elemental maps were constructed using characteristic Kα x-rays from the following elements: aluminum, silicon, sulfur, chlorine, potassium, calcium, iron, zinc, and strontium. The relative intensities of pixels in the elemental maps were used to categorize pixels in each image according to sand mastic, air voids, and aggregate using multi-spectral analysis techniques. Air void contents in the three images (A, B and C) are correlated to those computed from the asphalt concrete. It was found that the air void contents in the three images (A, B) are highly correlated to those computed from the asphalt concrete. The images were utilized to calculate aggregate gradations and compared with the real gradation. It is concluded that the microstructure characterization technique to capture the multi-phase nature of asphalt concrete using x-ray microfluorescence was moderately successful.

Development of femtosecond X-ray source in helium atmosphere with millijoule high-repetition-rate femtosecond laser

High intensity Cu Kα X-ray was generated in helium at atmospheric pressure (760 torr) using a commercial millijoule high-repetition rate Ti: sapphire laser. The characteristic Kα X-ray was generated by focusing the 0.06 mJ－1.46 mJ, 100 fs and 1 kHz repetition femtosecond laser onto a solid Cu target to a spot with a 5 μm diameter. We obtained the characteristic Kα X-ray of 5.4 × 109 photos/s into 2π sr at a 1 kHz repetition rate with 5.0 × 10-6 conversion efficiency. Kα X-ray intensity can be enhanced with 4－8% prepulse plasma into 7.7 × 109 photos/s/sr with 6.8 × 10-6 conversion efficiency. The X-ray intensity and conversion efficiency in helium achieved the almost the same level as in vacuum. Such vacuum-free femtosecond X-ray source with a tabletop laser can be a promising and easy accessible tool for time-resolved X-ray diffraction and other radiographic applications. The time-resolved X-ray diffraction experiment would reveal the ultrafast dynamics in crystalline materials, such as coherent phonon vibrations and ultrafast phase transitions.

Determination of lanthanides by source excited energy dispersive X-ray fluorescence (EDXRF) method after preconcentration with ammonium pyrrolidine dithiocarbamate (APDC)

A new analytical procedure for determination of lanthanides in environmental samples after chemical separation from major matrix elements on DOWEX 50W-X8 resin followed by preconcentration with chelating agent ammonium pyrrolidine dithiocarbamate (APDC) and analyses of thin targets by energy dispersive X-ray fluorescence (EDXRF) method using 109Cd as the source of excitation was presented. Characteristic Lα X-ray lines of the lanthanides were used for calculations of the net peak area and mass concentrations. The influence of pH value of the solution and addition of organic matter on the complexation was investigated. Percentage of recovery of each lanthanide after separation on DOWEX 50W-X8 resin was also determined. Accuracy of the method was tested on standard reference materials and real environmental samples (red mud material). For that purpose samples of standard reference materials and red mud were prepared as thick targets and directly analyzed (without the separation step) by EDXRF method using 241Am as the excitation source. In that case lanthanides concentrations were determined over their characteristic Kα X-ray lines and results were compared with those obtained after separation/preconcentration step described above. Results showed that selected lanthanides made stable complexes with APDC in the alkaline medium with the maximum recovery at pH = 8. The presence of organic matter slightly modified the complexation by means of somewhat higher recovery percentage at pH lower than 7 and approx. 20% lower recovery at pH higher than 7. Recovery of the elements after separation on DOWEX 50W-X8 resin and preconcentration with APDC at pH = 8 varied from 91.4% (Pr) to only 24.9% in the case of Dy. Concentrations of lanthanides measured in standard reference material and environmental samples of red mud after microwave digestion, separation on DOWEX 50W-X8 resin, preconcentration with APDC at pH = 8 and recalculation on the percentage of recovery were in good agreement with certified values in the case of SRM as well as with the concentrations obtained by direct determination over Kα lines using 241Am excitation source in the case of red mud leading to the conclusion that presented method was applicable for the determination of lanthanides in real environmental samples.

Investigation of the pre-edge inelastic X-ray scattering by several 3d transition-metal compounds

Abstract Spectra of X-rays scattered by compounds of 3d transition elements exhibit structure when the energies of the incident X-rays are a few electronvolts below the elements' K-absorption edge energies. This structure is the result of an inelastic scattering process and has been studied in compounds of chromium, iron and copper with a high-energy resolution wavelength-dispersive spectrometer. When the energies of the incident X-rays were tuned between the preedge peak and the absorption edge, the energy of the resonantly scattered X-rays were always measured to be equal to the energy of the characteristic Kα X-rays. This observation is in disagreement with the prediction of the present theoretical models for resonant scattering which were derived assuming the interactions to be fast collisions.

Charged particle track structure parameters for application in radiation biology and radiation chemistry

Chemical and biological damage, caused by directly or indirectly ionizing radiations, is attributable to the action of the charged particle tracks in the absorbing medium. Attempts to elucidate the biophysical mechanisms involved, and to quantify the damage, are typically made in terms of one or more of the main physical parameters descriptive of the charged particle tracks. To meet a need for a ready reference source of such information, tables of the relevant parameters have been calculated for a liquid water medium. The full tables are obtainable elsewhere. Here, a description is given of the quantities calculated and an extended example is given of their application in elucidating the physical mechanisms of radiation-induced biological damage. A representative selection of data is displayed graphically to illustrate the extent of the information obtained and its value in, e.g., application to fundamental radiation dosimetry. Track structure data is tabulated for instantaneous energies of individual particles and for the fluence and dose-weighted spectra at charged particle equilibrium. Data are listed for incident electrons (50 eV to 30 MeV); characteristic Kα X-rays from carbon to uranium; commonly used radioisotope sources of 241Am, 137Cs, and 60Co and for continuous X-ray spectra (⩽300 kV); Auger electron and beta-emitter radionuclides; heavy charged particles having specific energies of 0.5 keV/μ to 1 GeV/μ for 74 ion types ranging from protons to uranium ions, and for monoenergetic neutrons (0.5 keV to 100 MeV). Quantities listed are kerma factors; fluence of charged particles per unit source concentration; buildup factors; track and dose-average LET and restricted LET; W values; z2/β2;β2; delta-ray yields, energies, and ranges; ion ranges; and the mean free path for primary ionization and the linear primary ionization. For indirectly ionizing radiations, the microdose quantities, frequency, and dose means of lineal energy are tabulated along with typical energy deposition distribution spectra for neutrons and gamma rays in micron and nanometer volumes. © 1994 John Wiley & Sons, Inc.

Thickness measurements of thin films: comparison of techniques using characteristic X-ray line ratio techniques

In this research, two characteristic X-ray line ratio techniques are experimentally investigated. One technique uses the ratio of the characteristic L X-ray line to the characteristic Kα X-ray line of the substrate. The other techniques uses the ration between one characteristic X-ray line of the substrate and one characteristic X-ray line of the thin film overlay. Experimental measurements were taken for both techniques by bombarding a coated sample with electrons and measuring the ratio of the areas under the characteristic X-ray line peaks. The samples used in the experiment consisted of a copper substrate coated with aluminum and a molybdenum substrate coated with aluminum. The data are presented by plotting the characteristic X-ray line ratio vs. the thin film thickness from 400 to 7000 Å for 20, 25 and 30 keV electron bombardment. On the basis of these experiments, it was found that the ratio of the characteristic X-ray lines from the substrate (L:Kα ratio) is not suitable for thin film measurements because of the complication caused by matrix enhancement effects. However, matrix enhancement effects are also partly responsible for producing a large ratio change (80%) over the range of 5000 Å of overlay coating for the ratio technique that uses an X-ray line from the substrate and an X-ray line from the thin film overlay. This ratio was independent of accelerating electron energy and inversely proportional to the thickness.