Low Atomic Number Elements Research Articles

Determinations of low atomic number elements in real uranium oxide samples using vacuum chamber total reflection x-ray fluorescence

Conditions for the total reflection x-ray fluorescence (TXRF) analysis of real uranium samples for low atomic number elements using vacuum chamber TXRF spectrometer were optimized. It was observed that for analysis of low atomic number elements, almost complete removal of uranium matrix is required. Two certified reference materials of uranium containing trace elements in different concentrations were dissolved in minimum amount of high purity nitric acid. The uranium matrix from these solutions was separated by solvent extraction using tri-n-butyl phosphate as extracting reagent. Low atomic number elements in TXRF spectrum of the aqueous phase could be seen only after six tri-n-butyl phosphate equilibrations in extraction. The TXRF determinations of the certified low atomic number elements Mg and Al were made in these aqueous solutions after addition of Sc as an internal standard. The TXRF determined values for Mg were in good agreement with the certified values, whereas TXRF determined Al values differed from the certified values appreciably, probably due to the interference of Al Kα peak with escape peak of U Mα and the neighboring Si Kα peak. Copyright © 2013 John Wiley & Sons, Ltd.

Trace detection of light elements by laser-induced breakdown spectroscopy (LIBS): Applications to non-conducting materials

The existence as well as concentration of light (low-atomic number) elements is directly related to some of the most important properties of almost all materials. Thus, the development of a direct, fast, and sensitive spectroscopic method for the analytical quantification of these elements is considered an important continuing challenge in many fields. In this report, results obtained from previous as well as most recent studies regarding trace detection of light elements in non-conducting materials by laser-induced breakdown spectroscopy (LIBS) technique are reviewed for the first time. Firstly, we introduce investigations performed in the far- and vacuum-UV as well as UV-visible-NIR spectral domains, and cover many non-conducting materials including gases, aerosols, soil, cement, and selected organic compounds. The report also demonstrates important analytical results for the elements lithium, beryllium, boron, carbon, fluorine, phosphorus, sulfur, and chlorine. In addition, key characterization information relating to a specific element in a given matrix and state is summarized in such a way that relevant resources can easily be traced. Furthermore, in order to facilitate tracking down the evolution of the technique for a particular material category, a chronological order has been devised. In the second part of the review, the latest developments and advances in instrumentation and methodologies of the LIBS technique, particularly in the realm of light elements detection, are discussed. The sensitive detection of light elements in the UV-VIS-NIR is still unsatisfactory, and more work is needed in order to achieve better analytical performance in terms of precision, accuracy and limits of detection. The author anticipates that significant sensitivity improvements should be realized by combining LIBS, employing femtosecond laser pulses, with other diagnostic techniques based on probing the plasma via diode lasers.

Enhanced x-ray detection sensitivity in semiconducting polymer diodes containing metallic nanoparticles

Semiconducting polymer X-radiation detectors are a completely new family of low-cost radiation detectors with potential application as beam monitors or dosimeters. These detectors are easy to process, mechanically flexible, relatively inexpensive, and able to cover large areas. However, their x-ray photocurrents are typically low as, being composed of elements of low atomic number (Z), they attenuate x-rays weakly. Here, the addition of high-Z nanoparticles is used to increase the x-ray attenuation without sacrificing the attractive properties of the host polymer. Two types of nanoparticles (NPs) are compared: metallic tantalum and electrically insulating bismuth oxide. The detection sensitivity of 5 µm thick semiconducting poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene) diodes containing tantalum NPs is four times greater than that for the analogous NP-free devices; it is approximately double that of diodes containing an equal volume of bismuth oxide NPs. The x-ray induced photocurrent output of the diodes increases with an increased concentration of NPs. However, contrary to the results of theoretical x-ray attenuation calculations, the experimental current output is higher for the lower-Z tantalum diodes than the bismuth oxide diodes, at the same concentration of NP loading. This result is likely due to the higher tantalum NP electrical conductivity, which increases charge transport through the semiconducting polymer, leading to increased diode conductivity.

Atom Probe Tomography of Apatites and Bone-Type Mineralized Tissues

Nanocrystalline biological apatites constitute the mineral phase of vertebrate bone and teeth. Beyond their central importance to the mechanical function of our skeleton, their extraordinarily large surface acts as the most important ion exchanger for essential and toxic ions in our body. However, the nanoscale structural and chemical complexity of apatite-based mineralized tissues is a formidable challenge to quantitative imaging. For example, even energy-filtered electron microscopy is not suitable for detection of small quantities of low atomic number elements typical for biological materials. Herein we show that laser-pulsed atom probe tomography, a technique that combines subnanometer spatial resolution with unbiased chemical sensitivity, is uniquely suited to the task. Common apatite end members share a number of features, but can clearly be distinguished by their spectrometric fingerprint. This fingerprint and the formation of molecular ions during field evaporation can be explained based on the chemistry of the apatite channel ion. Using end members for reference, we are able to interpret the spectra of bone and dentin samples, and generate the first three-dimensional reconstruction of 1.2 × 10(7) atoms in a dentin sample. The fibrous nature of the collagenous organic matrix in dentin is clearly recognizable in the reconstruction. Surprisingly, some fibers show selectivity in binding for sodium ions over magnesium ions, implying that an additional, chemical level of hierarchy is necessary to describe dentin structure. Furthermore, segregation of inorganic ions or small organic molecules to homophase interfaces (grain boundaries) is not apparent. This has implications for the platelet model for apatite biominerals.

A Computational Study of a Capillary Discharge Pellet Accelerator Concept for Magnetic Fusion Fueling

An ablation-dominated capillary discharge using low atomic number elements for plasma formation to flow into an ablation-free extension barrel is a concept that provides a high energy–density plasma flow sufficient to propel fuel pellets into the tokamak fusion plasma chamber. In this concept, the extension barrel is made from a non-ablating material by coating the interior wall of the barrel with nanocrystalline diamond to eliminate mixing the propelling plasma with any impurities evolving from the barrel ablation. The electrothermal plasma code ETFLOW models the plasma formation and flow in the capillary discharge and the flow into the extension barrel to accelerate frozen deuterium pellets. The code includes governing equations for both the capillary and the extension barrel, with the addition of the pellet’s terms. It also includes ideal and non-ideal plasma conductivity models. The joule heating term in the energy conservation equation is only valid in the capillary section. The pellet momentum and kinetic energy are included in the governing equations of the barrel, with the addition of the effect of viscous drag terms. The electrothermal capillary source generates the plasma via the ablation of a sleeve inside the main capillary housing. The acceleration of the pellet starts in the extension barrel when the pressure of the plasma flow from the capillary reaches the release limit. The code results show pellet exit velocities in excess of 2 km/s for source/barrel systems with low-Z liner materials in the source for 5, 20, 45, and 80 mg pellets. The study shows that an increase in the length of both the source and the extension barrel increases the pellet exit velocity with the limitation of slowdown effects for plasma expansion and cooling off inside the barrel.

Calibration of the Mars Science Laboratory Alpha Particle X-ray Spectrometer

The alpha-particle X-ray spectrometer (APXS) for the Mars Science Laboratory (MSL) mission was calibrated for routine analysis of: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Br, Rb, Sr, and Y. The following elements were also calibrated, but may be too low to be measured (10s–100s ppm) for their usual abundance on Mars: V, Cu, Ga, As, Se and W. An extensive suite of geological reference materials, supplemented by pure chemical elements and compounds was used. Special attention was paid to include phyllosilicates, sulfates and a broad selection of basalts as these are predicted minerals and rocks at the Gale Crater landing site. The calibration approach is from first principles, using fundamental physics parameters and an assumed homogeneous sample matrix to calculate expected elemental signals for a given instrument setup and sample composition. Resulting concentrations for most elements accord with expected values. Deviations in elements of lower atomic number (Na, Mg, Al) indicate significant influences of mineral phases, especially in basalts, ultramafic rocks and trachytes. The systematics of these deviations help us to derive empirical, iterative corrections for different rock groups, based on a preliminary APXS analysis which assumes a homogeneous sample. These corrections have the potential to significantly improve the accuracy of APXS analyses, especially when other MSL instrument results, such as the X-ray diffraction data from CheMin, are included in the overall analysis process.

Elemental and structural studies at the bone–cartilage interface

Micro-Proton Induced X-ray Emission (μ-PIXE) and Proton Induced Gamma-ray Emission (PIGE) techniques were employed in the investigation of trace and essential elements distribution in normal and diseased human femoral head sections affected by osteoarthritis (OA). PIGE was exploited in the determination of elements of low atomic number z<15 such as Na and F whereas elements with z>15 viz Ca, Z, P and S were determined by PIXE. Accumulations of key elements in the bone and cartilage sections were observed, significant S and Na concentrations being found in the cartilage region particularly in normal tissues. Zn showed enhanced concentrations at the bone–cartilage interface. At a synchrotron facility, small angle X-ray scattering (SAXS) was utilized on a decalcified human femoral head section affected by OA, direct measurements being made of spatial alterations of collagen fibres. The SAXS results showed a slight decrease in the axial periodicity between normal collagen type I and that in diseased tissue in various sites, in contrast with the findings of others.

Vacancy Transfer Probabilities from K to L Shell for Low Atomic Number Elements at 5.96 keV

Vacancy Transfer Probabilities from K to L Shell for Low Atomic Number Elements at 5.96 keV

Determination of low atomic number elements at trace levels in uranium matrix using vacuum chamber total reflection X-ray fluorescence

Determinations of low atomic number elements Na, Mg and Al present at trace concentrations in uranium matrix were made by vacuum chamber total reflection X-ray fluorescence spectrometer for the first time. For this purpose, synthetic samples of uranium with known amounts of these low atomic number elements were prepared by mixing different volumes of their solutions with U solution of high purity. The concentrations of these elements in the samples were in the range of 100–300 μg/g with respect to uranium and 10–20 μg/mL in the solutions. Major matrix uranium was separated by solvent extraction with 30% solution of tri-n-butyl phosphate in dodecane. After the solvent extraction, aqueous phase containing trace elements was mixed with Sc internal standard and the samples were analyzed by vacuum chamber total reflection X-ray fluorescence spectrometer having a Cr Kα excitation source. The total reflection X-ray fluorescence results obtained, after blank corrections, indicated an average deviation of 14% from the calculated concentrations of these low atomic number elements on the basis of their preparation. However, the total reflection X-ray fluorescence determined concentration of Mg was exceptionally lower than the calculated concentration in two samples. These studies have shown that vacuum chamber total reflection X-ray fluorescence is a promising technique for the determination of low atomic number elements in uranium matrix after its separation.

Synchrotron-based scattered radiation from phantom materials used in X-ray CT

Synchrotron-based scattered radiation form low-contrast phantom materials prepared from polyethylene, polystyrene, nylon, and Plexiglas is used as test objects in X-ray CT was examined with 8, 10 and 12 keV X-rays. These phantom materials of medical interest will contains varying proportions of low atomic number elements. The assessment will allowed us to estimate the fluorescence to total scattered radiation. Detected the fluorescence spectra and the associated scattered radiation from calcium hydroxyapatite phantom with 8, 10 and 12 keV synchrotron X-rays. Samples with Bonefil (60% and 70% of calcium hydroxyapatite) and Bone cream (35 approximately 45% of calcium hydroxyapatite), were used. Utilized the X-ray micro-spectroscopy beamline facility, X27A, available at NSLS, BNL, USA. The primary beam with a spot size of the order of approximately 10 mum, has been used for focusing. With this spatial resolution and high flux throuput, the synchrotron-based scattered radiation from the phantom materials were measured using a liquid-nitrogen-cooled 13-element energy-dispersive high-purity germanium detector.

Determination of low atomic number elements by X-ray fluorescence fundamental parameter method

Two versions of the X-ray fluorescence fundamental parameter method are compared in the analysis of the materials that contain low atomic number elements (fluorine, oxygen, nitrogen, carbon, and boron). It is shown by the examples of carbon and oxygen that, in using the classical version, the account of C and O atom ionization by photo and Auger electrons of the irradiated sample is obligatory. A change to absolute intensities in combination with the regression approach makes the method more flexible. In particular, the computational modeling of analytical signals for elements with Z < 10 becomes possible without taking into account the ionizing effect of photo and Auger electrons when the contribution of these electrons to the fluorescence intensity changes insignificantly. The error of the analysis grows with an increase in the variation of this contribution. If the contributions for the test samples differ significantly, the computational modeling of the effect of photo and Auger electrons in the iterative process becomes necessary.

Self-assembled monolayer fiducial grids for spatial-phase-locked electron-beam lithography

The authors characterize a new fiducial grid based on a self-assembled monolayer (SAM) that is well suited to low-energy (⩽10keV) spatial-phase locked electron-beam lithography (SPLEBL). SAMs significantly alter the secondary electron yield of the metal films on which they are formed. In addition, SAMs are not expected to strongly scatter the primary beam, even at low energies, because they are less than 2-nm-thick and are composed of low atomic number elements. In this work the authors evaluate the signal-to-noise ratio (SNR) of SAM grids on gold and copper coated electron-beam resist. 400nm period octadecanethiol fiducial grids were microcontact printed onto the gold and copper metal layers using polydimethylsiloxane stamps. Gold serves as a model system and provides excellent SNR; however, its strong forward scattering makes it impractical in many applications. Copper offers reduced forward scattering but exhibits inverted secondary electron contrast and greatly reduced SNRs. In all cases, SNR decreases with increasing beam energy as overall secondary electron yield decreases. These results suggest that SAM fiducial grids are promising for low-energy SPLEBL; however, further optimization of the interlayer and SAM composition is warranted.

Glass formation and optical properties of CdGeAs2 alloys

Abstract Cadmium germanium arsenide (CGA), CdGeAs 2 , is a chalcopyrite-structured non-linear optical crystal with a high non-linear optical coefficient ( d 36 =236 pm/V) and a transparency range of 2.3–18 μm. This compound is also known to be a glass-former when quenched from a melt. In this study, the glass-forming ability of CGA alloyed with different amounts of P, Sn, Sb, and Pb is examined, and the optical properties of CGA single crystals are compared to those of the amorphous CGA samples. The glass-forming ability of the alloyed compounds was determined using powder X-ray diffraction, and glass transition and recrystallization temperatures were measured using differential scanning calorimetry. Glass formation ranges were measured to be: 0⩽ x ⩽1 for CdGe(As (1− x ) P x ) 2 , 0⩽ x ⩽0.4 for CdGe (1− x ) Sn x As 2 , 0⩽ x ⩽0.2 for CdGe(As (1− x ) Sb x ) 2 , and 0⩽ x ⩽0.1 for CdGe (1− x ) Pb x As 2 . The glass transition temperature of amorphous CGA decreased with the addition of Sn, Sb, and Pb and increased with the addition of P. Optical spectra were measured for the CGA single crystals and the alloyed glasses. The optical band gaps in all of the CGA glass alloys were measured to be higher than that of the CGA crystal (0.54 eV). The optical band gap of the CGA glass alloys increased with the addition of lower atomic number elements (P), and decreased with the addition of higher atomic number elements (Sn, Sb, Pb).

Characterization of pyrocarbon coated materials using laboratory based x-ray phase contrast imaging technique

In-line x-ray phase contrast is an emerging x-ray imaging technique that promises to improve the contrast in x-ray imaging process. This technique is most suited for x-ray imaging of soft materials, low atomic number elements such as carbon composite fibers, very thin coatings, etc. We have used this new emerging technique for visualization and characterization of the pyrocarbon coated materials using a combination of microfocus x-ray source and x-ray charge coupled device detector. These studies are important for characterization of coating and optimization of various process parameters during deposition. These experiments will help us to exploit the potential of this technique for studies in other areas of material science such as characterization of carbon fibered structures and detection of cracks and flaws in materials. The characterization of the imaging system and optimization of some process parameters for carbon deposition are also described in detail.

Phase separation in the crust of accreting neutron stars

Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus.

Application of Microfocus X-ray Generator and Charge-Coupled Device Camera for Refraction Contrast Radiography

The X-ray imaging of materials with low atomic number elements is difficult through a conventional photoabsorption contrast method whereas much higher contrast can be achieved by phase-contrast imaging. We have constructed a compact size imaging system using a microfocus X-ray generator with a few µm spot size. We present here the evaluation of basic characteristics and sample results, as well as future prospects.

Total reflection X-ray fluorescence analysis of river waters in its stream across the city of Cordoba, in Argentina

The aim of this work was to analyze the composition of river waters and to study their quality by detecting possible contaminants. The samples were taken at 32 points of the Suquía River in its stream across the city of Córdoba (in the Province of Córdoba, Argentina). The samples were analyzed with total reflection X-ray fluorescence (TXRF) using beam guides. Beam guides made of two Si plate reflectors were used as sample carriers and to guide the X-ray photons to the sample; the measurements were taken using the characteristic configuration that ensures the best excitation and detection conditions (in TXRF). The analyses were carried out by preconcentration of the water samples and by adding an internal standard (Gallium); small amounts of samples (30 μl) were deposited on the Si reflector plate and they were then analyzed in the total reflection regime. Spectra were analyzed with standard methods using conventional programs. The results show interesting behaviors of the concentration of trace elements along the river: elements of low atomic number (such as Ca, Cl, S, K) present higher concentrations as compared to high Z elements (such as Fe, Zn, Br, Sr); the concentrations of light elements follow a similar behavior along the stream, the same situation is observed in the set of elements with high atomic number. Some samples present high concentrations in certain elements indicating possible sources of contamination.

2004–2005 Analytical Developments in Secondary Ion Mass Spectrometry

This review of the literature from 2004 and 2005 concerning secondary ion mass spectrometry (SIMS) highlights the contribution the technique has made in the fields of petrology, geochronology, cosmochemistry and material sciences. In petrology, much research was devoted to the measurement of stable isotopes and trace elements by developments in multicollection acquisition, with emphasis on low atomic mass number elements. Elements studied in particular were S (in sulfides), O (in garnets), C (in sedimentary organic matter), Cl (in glasses) and Si. Novel applications of SIMS to geochronology have included the measurement of young zircon grains by the U‐Pb and U‐Th decay methods. An increasing number of studies have combined U‐Pb geochronology with the measurement of trace elements or stable isotopes in zircon.

‘‘Hybrid’’ calibrations of a Dual Energy X-ray Scanner for material testing

Conventional x-ray tubes produce a fan-shaped x-ray beam covering a large spectrum of energies, which is why the fundamental law of x-ray attenuation is not readily applicable. As the mathematical formulation of the problem would be too cumbersome, calibrations using well-defined objects are carried out, which in turn allow the use of multienergy x-rays for measurements. Occasionally, such calibrations may not lead to the desired results. This could be for instance due to an insensitivity of x-rays towards low atomic number elements. Here we present such a case on hand the example of raw natural fibre. The DEXA parameters correlated with the fibre parameter wool base, but show distinct correlation for geographical regions of the origin of the wool. A calibration that is valid independently of geographical origin can be achieved by including independently measured parameters of the calibration body. We demonstrate a successful calibration that uses dual energy x-ray scanning technology as well as a size parameter of the fibre in the regression equation.

Experimental study of coherence and correlation in the anisotropy of NeKL-LLLsatellite Auger decay

The coherent excitation of overlapping atomic states by ion projectiles has a strong effect on the angular distribution of Auger electrons. Therefore, the measurement of the angular anisotropy of outgoing Auger electrons is suitable for the quantitative studies of the influence of the coherence. In our experiment the Ne target was bombarded with $700--2000\phantom{\rule{0.3em}{0ex}}\text{keV}$ ${\mathrm{H}}^{+}$ and $2000\phantom{\rule{0.3em}{0ex}}\text{keV}$ ${\mathrm{He}}^{+}$ projectiles. The angular distributions of ${KL}_{2,3}{\text{\ensuremath{-}}LLL}_{2,3}$ Auger electrons emitted from the decay of the coherently excited $1s2p$ doubly vacancy states of Ne were measured. The anisotropy parameter of the Auger decay was deduced from the measurements and compared with theoretical results calculated using the multiconfiguration Dirac-Fock method. The results indicate that one should go beyond the $LS$ coupling scheme even at this relatively low atomic number element, but also suggest that only partially overlapping states need to be taken into account.