Recent developments in chemical characterization with MeV ion beams

A multitude of ion-atom interactions are induced with projectiles of E0.1 MeV/nucleon. Analytical techniques derived from these include particle induced X-ray emission (PIXE), charged particle activation analysis (CPAA), prompt nuclear reactions (PNR), and Rutherford backscattering spectrometry (RBS). Among their features are broad elemental coverage (PIXE), subnanogram sensitivity (PIXE, CPAA), isotopic specificity (CPAA, PNR), and depth resolution (RBS, PNR). A limiting requirement with each technique is the need for high intensity ion beams. Novel approaches seek now to obtain analytical information with very small numbers of bombarding ions. Sample integrity is then maintained; moreover, they can be delivered in a microbeam (diameter 5 mm). A phenomenon which under these conditions provides useful analytical information is the particle induced desorption of molecular fragments. Thus, microscopic chemical analysis can be achieved with a small number (<10,000) of heavy fast projectiles and identification of the species desorbed from the sample surface via time-of-flight mass spectrometry. Experimental work with 84 MeV kr ions indicates the following: (a) high desorption yields can be obtained (>50%); (b) mass spectrometry on microspots (diameter of a few m) is feasible; (c) < 10⁶ atoms can be detected. Further capabilities of ion beams for minute, detailed, and comprehensive chemical characterization remain to be explored.     

Radiochemistry as a tool in RIB studies

Radiochemistry can be an important tool in studies of nuclear reactions induced by radioactive ion beams (RIBs). RIB intensities are typically 10³–10⁵ particles/s leading to very low reaction rates. The sensitivity of radiochemical methods and the ability to uniquely determine the atomic properties of the reaction products offer substantial advantages. The application of radiochemical techniques to study the fusion of ^9,11Li with ⁷⁰Zn and the “inverse fission” of uranium is described.     

Are cluster ion analysis beams good choices for hydrogen depth profiling using time‐of‐flight secondary ion mass spectrometry?

For more than three decades, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used for elemental depth profiling. In recent years, cluster primary ion sources (principally, C₆₀⁺, Bi_n⁺, and Au_n⁺) have become widely available, and they can greatly enhance the signal intensity of molecular ions (10–1000 times). Understanding the performance of cluster ion analysis beams used in elemental depth profiling can greatly assist normal ToF‐SIMS users in choosing the optimal analysis beam for depth profiling work. Presently, however, the experimental data are lacking, and such choices are difficult to make. In this paper, hydrogen and deuterium depth profiling were studied using six different analysis beams—25 keV Bi⁺, Bi₃⁺, Bi₅⁺, 50 keV Bi₃²⁺, 10 keV C₆₀⁺, and 20 keV C₆₀²⁺. The effort shows that cluster primary ions do enhance H^? and D^? yields, but the enhancement is only about 1.5–4.0 times when compared to atomic Bi⁺ ions. Because the currents of atomic ion analysis beams are much stronger than the currents of cluster ion analysis beams for most commercial ToF‐SIMS instruments, the atomic ion analysis beams can provide the strongest H^? and D^? signal intensities, and may be the best choices for hydrogen and deuterium depth profiling. In addition, two representative nuclides, ³⁰Si and ¹⁸O, were also studied and yielded results similar to those of H^? and D^?. Copyright © 2011 John Wiley & Sons, Ltd.     

Nuclear and atomic activation with heavy ion beams

Heavy ion activation has been studied as a method for determining hydrogen. The reactions used [e.g.¹H(⁷Li, n)⁷Be] are the “inverse” of well known reactions [e.g.⁷Li(p, n)⁷Be]. Nuclear activation parameters for the ion beams of interest (⁷Li²⁺,¹⁰B²⁺) have been studied. The analytical feasibility is demonstrated with the determination of hydrogen in titanium at the 100 and 30 ppm levels with relative precisions of 8 to 10%. Detection limits in titanium are in the 0.1 to 0.5 ppm range. Heavy ion bombardment is also accompanied by the emission of characteristic X-rays (“atomic” activation). The parameters governing X-ray emission and background production have been investigated. Experimental K and L X-ray yields from thick targets have been measured for many elements excited by Oⁿ⁺ beams of 0.5 to 7 MeV/amu and Kr⁷⁺ beams of 0.5 to 1 MeV/amu. The simultaneous determination of trace elements at levels of 10 to several 100 ppm in microsamples (∼10⁻⁵ g) is demonstrated on biological specimens. K and L X-ray yields and corresponding detection limits have also been measured with the⁷Li²⁺ and¹⁰B²⁺ beams used for the nuclear activation of hydrogen. With these beams (∼6 MeV/amu) simultaneous nuclear and atomic activation is possible, yielding an unusual multielement trace analysis capability covering hydrogen and medium and high Z elements.     

Determination of trace impurities in electronic grade quartz: Comparison of inductively coupled plasma mass spectroscopy with other analytical techniques

An analytical procedure for the determination of uranium and thorium in the sub-ng/g range as well as of other trace elements in the ng/g to g/g range in high purity quartz samples is described. The results obtained by inductively coupled plasma mass spectroscopy (ICP-MS) are compared to those obtained by other analytical techniques (instrumental neutron activation analysis, INAA; flame atomic absorption spectrometry, AAS; Zeeman graphite furnace atomic absorption spectrometry, ZGFAAS; total reflection X-ray fluorescence analysis, TRFA; direct current arc optical emission spectrometry, DC-arc OES; and X-ray fluorescence analysis, XRFA). For the ICP-MS measurements, the decomposition of the samples is carried out with HF/HNO₃/H₂SO₄-mixtures. The results obtained by the different methods show reasonable agreement. For uranium and thorium, ICP-MS proves to be the most sensitive method: detection limits of about 50 pg/g can be achieved for both elements.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Prompt and delayed radiation measurements in the elemental analysis of biological materials: The case for neutron induced gamma-ray emission tomography

Nuclear and atomic methods of analysis, which rely on the detection of prompt and delayed radiations, emitted as a result of interactions between radiation probe and target, for determining the elemental concentration in vivo and in vitro, are summarily reviewed, with reference to bone analysis; the demand for methods which provide information about elemental distribution is highlighted. The way neutrons can be used as probes to investigate the composition and structure of objects by employed the principles of computerised tomography are outlined and the novel modes of utilisation are briefly described: neutron transmission tomography, neutron induced prompt gammaray emission tomography and neutron induced delayed gamma-ray emission tomography. The latter method, alternatively termed neutron activation tomography, is then used to determine on-destructively the distribution of Na in selected planes of a human tibia, in vitro, by measuring the activity of²⁴Na using a NaI(Tl) and a Ge(Li) detector in a tomographic scanner which incorporates a microcomputer for control, data acquisition and image reconstruction. The problems of attenuation and scattering are discussed as are the limitations for quantitative results of this useful new mode of tomography which provided information about composition and elemental distribution in a material.     

Analytical techniques with a nuclear microprobe

Nuclear microprobes have proved to be versatile tools to perform investigations in materials science with a lateral resolution of typically 1 to 10 m. Many of the commonly utilized ion beam assisted analytical techniques, like PIXE (Particle Induced X-Ray Emission), RBS (Rutherford Back Scattering), NRA (Nuclear Reaction Analysis), and Channeling can be applied with a nuclear microprobe. Additionally, there are methods typical for the nuclear microprobe, e.g. STIM (Scanning Transmission Ion Microscopy). The nuclear microprobe used here has been applied successfully to the analysis of geological and biological specimens and is currently being modified by the introduction of a superconducting solenoid as focusing element to allow higher lateral resolution. Especially the analysis and modification of electronic devices will become possible. An overview of the analytical techniques practiced with the nuclear microprobe is given with emphasis on laterally resolved trace element analysis.     

Accelerator based techniques for trace element analysis on the micrometer scale

Summary Accelerators, capable of producing beams of ions up to several MeV are frequently used for (micro-)analytical purposes. In the majority of cases, the activities are centered around an accelerator previously exclusively used for studies in nuclear physics; but recently, at a number of laboratories completely dedicated analytical accelerators have been installed. In this paper an overview is given of the analytical possibilities opened up with the availability of these ion beams.     

Analysis of ionic solids with SNMS

Summary The application of plasma-based SNMS to salt samples was examined to reveal the analytical features of this technique for the analysis of environmental material, which is frequently composed of ionic compounds. 10¹⁶ s^–1 cm^–2 argon ions of 300–500 eV energy were used to sputter halides, sulfates, nitrates and carbonates. The mass spectra are dominated by atomic signals of all elements of the salt and contain additional minor signals of binary homo- and heteroelemental clusters. The latter, such as salt monomers of alkali halides, are useful for compound identification. In sputter equilibrium the atomic mass signals can be used for elemental quantitation with a matrix dependence of about ±30% for the detection factors of most elements. As the average elemental detection factors are shown to be governed by atomic ionization probabilities the erosion flux from salts comprises mainly atoms. Results indicate that thermal release of atoms as well as emission of clusters are the main cause of the matrix dependence. The relative yield of the clusters was found to be strongly enhanced with increasing mass difference of the combined ions. The sputter yield of NaCl was determined to be 3.3 atoms/projectile at 490 eV argon ion energy which results in a depth propagation of 5 nm/s for the given sputter conditions.     

The use of plasma atomic spectrometric methods for the analysis of ceramic powders

The use of plasma atomic spectrometric methods for the analysis of high-purity refractory powders of Al₂O₃, SiC and ZrO₂ used in the production of advanced ceramics is discussed. Special reference is given to the use of combined procedures including sample decomposition and in the case of ZrO₂ to matrix removal as well as to the slurry technique as a direct method in atomic spectrometry with inductively coupled plasmas (ICP). Both the possibilities, limitations and analytical use of the slurry technique are discussed and shown to be related to the particle size of the powder; this should be below the 5–10 m level. The use of a Simplex method for the optimization of the slurry technique towards obtaining both the highest power of detection and calibration using solutions will be treated for the case of SiC. A critical evaluation of the use of ICP atomic emission and of ICP mass spectrometry is presented.     

Doppler-broadened line shapes of atomic hydrogen in a parallel-plate radio frequency discharge

Doppler-shifted atomic hydrogen emission (Balmer ) is observed from a low-frequency rf discharge through molecular hydrogen by collecting the light through a hole in one of the electrodes. Doppler shifts as large as 0.7 nm, corresponding to an energy of 540 eV or 85% of the peak applied voltage, are observed when ions are accelerated by the sheath electric field. The mechanisms for hot atom production are discussed in terms of both gas-phase and surface ion-impact phenomena. Hot atoms are produced via gas-phase ion-atom and ion-molecule collisions, as a result of simultaneous neutralization and reflection of ions at the electrode surface, and/or by sputtering of adsorbed hydrogen. As much as 30% of the atomic hydrogen emission is substantially Doppler shifted, indicating that most of the atomic emission in the sheaths is actually produced by ion impact and not by electron impact.     

On the history of cluster beams

The methods to produce and investigate cluster beams have been developed primarily with the use of permanent gases. A summary is given of related work carried out at Marburg and Karlsruhe. The report deals with the effect of carrier gases on cluster beam production; ionization, electrical acceleration and magnetic deflection of cluster beams; the retarding potential mass spectrometry of cluster beams; cluster size measurement by atomic beam attenuation; reflection of cluster beams at solid surfaces; scattering properties of⁴He and³He clusters; the application of cluster beams in plasma physics, and the reduction of space charge problems by acceleration of cluster ions.     

Peptide–Column Interactions and Their Influence on Back Exchange Rates in Hydrogen/Deuterium Exchange-MS

Hydrogen/deuterium exchange (HDX) methods generate useful information on protein structure and dynamics, ideally at the individual residue level. Most MS-based HDX methods involve a rapid proteolytic digestion followed by LC/MS analysis, with exchange kinetics monitored at the peptide level. Localizing specific sites of HDX is usually restricted to a resolution the size of the host peptide because gas-phase processes can scramble deuterium throughout the peptide. Subtractive methods may improve resolution, where deuterium levels of overlapping and nested peptides are used in a subtractive manner to localize exchange to smaller segments. In this study, we explore the underlying assumption of the subtractive method, namely, that the measured back exchange kinetics of a given residue is independent of its host peptide. Using a series of deuterated peptides, we show that secondary structure can be partially retained under quenched conditions, and that interactions between peptides and reversed-phase LC columns may both accelerate and decelerate residue HDX, depending upon peptide sequence and length. Secondary structure is induced through column interactions in peptides with a solution-phase propensity for structure, which has the effect of slowing HDX rates relative to predicted random coil values. Conversely, column interactions can orient random-coil peptide conformers to accelerate HDX, the degree to which correlates with peptide charge in solution, and which can be reversed by using stronger ion pairing reagents. The dependency of these effects on sequence and length suggest that subtractive methods for improving structural resolution in HDX-MS will not offer a straightforward solution for increasing exchange site resolution.

Radioactive beams — A new application of radioanalytical chemistry

An emerging, exciting area of nuclear science is the use of radioactive nuclear beams to study chemical and physical phenomena. One uses the radioactive products (ms<t_1/2<y) of nuclear reactions induced by charged particles or nuetrons to induce secondary reactions or to act as radiotracers. The use of such beams enhances the tools of the radioanalytical chemist. Applications of such beams in materials science (where the beams act as tracers), and the synthesis of new nuclei (especially with Z104) are described.     

Application of surface chemical analysis tools for characterization of nanoparticles

The important role that surface chemical analysis methods can and should play in the characterization of nanoparticles is described. The types of information that can be obtained from analysis of nanoparticles using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary-ion mass spectrometry (TOF-SIMS), low-energy ion scattering (LEIS), and scanning-probe microscopy (SPM), including scanning tunneling microscopy (STM) and atomic force microscopy (AFM), are briefly summarized. Examples describing the characterization of engineered nanoparticles are provided. Specific analysis considerations and issues associated with using surface-analysis methods for the characterization of nanoparticles are discussed and summarized, with the impact that shape instability, environmentally induced changes, deliberate and accidental coating, etc., have on nanoparticle properties.      

Analysis of high-temperature superconducting films by X-ray fluorescence analysis

Radionuclide X-ray fluorescence analysis was used for the determination of Cu, Y and Ba in very thin high-temperature superconducting films. The precision of the method is better than 3% for about 1 m thick films. The atomic emission ICP spectrometry was used to testify results of XRF analysis. An acceptable agreement of both methods was obtained.     

Operating mechanism of the electrolyte cathode atmospheric glow discharge

Cathode fall (U_cf), cathodic current density and atomic emission intensities originating from metal salts in the electrolyte cathode were measured as a function of different discharge parameters. Emission intensities in function of cathode fall indicate a potential barrier in the sputtered mass flux. This means that the primary particles of the cathode sputtering are of positive charge and the cathode fall including its internal variables is the most important factor. The measured current density and the U_cf as a function of pressure are in accordance with the low pressure data in the literature. The observed decrease of the U_cf with decreasing pH was explained by a model in that the secondary electron emission coefficient of the cathode () is controlled through a reaction net of competing reactions of different electron scavengers involving the hydroxonium ions of the cathode solution. The model revealed two different electron emission processes of the electrolyte cathode, an emission coupled with hydrated electrons is dominating below pH 2.5 while a proton-independent emission of poor efficiency is working above pH 3. Our model fits to the reported yields of the ultimate products both in the solution and in the gas phase and offers a calculation of and U_cf in the function of the cathode acidity. The model provides two other independent calculation methods based on product analysis data.     

Nuclear systematics: II. The cradle of the nuclides

The nuclear energy surface is presented as three-dimensional (3-D) plots of mass or atomic number versus charge density versus average energy per nucleon. These plots reveal a trough or cradle of the nuclides. Stable and long-lived nuclides are located in the valley. Those that are radioactive or are easily destroyed by fusion or fission occupy higher positions. Separate modes of nucleosynthesis fill the cradle from different directions and produce distinct occupancy levels, i.e., different abundance patterns. The cradle can be used to estimate the properties of nuclear matter that cannot be studied in the laboratory.     

Temperature-dependent size exclusion chromatography for the in situ investigation of dynamic bonding/debonding reactions

Polymers capable of dynamic bonding/debonding reactions are of great interest in modern day research. Potential applications can be found in the fields of self-healing materials or printable networks. Since temperature is often used as a stimulus for triggering reversible bonding reactions, an analysis operating at elevated temperatures is very useful for the in situ investigation of the reaction mechanism, as unwanted side effects can be minimized when performing the analyses at the same temperature at which the reactions occur. A temperature-dependent size exclusion chromatographic system (TD SEC) has been optimized for investigating the kinetics of retro Diels?Alder-based depolymerization of Diels?Alder polymers. The changing molecular weight distribution of the analyzed polymers during depolymerization gives valuable quantitative information on the kinetics of the reactions. Adequate data interpretation methods were developed for the correct evaluation of the chromatograms. The results are confirmed by high-temperature dynamic light scattering, thermogravimetric analysis, and time-resolved nuclear magnetic resonance spectroscopy at high temperatures. In addition, the SEC system and column material stability under application conditions were assessed using thermoanalysis methods, infrared spectroscopy, nitrogen physisorption, and scanning electron microscopy. The findings demonstrate that the system is stable and, thus, we can reliably characterize such dynamically bonding/debonding systems with TD SEC.

Die entwicklung edelmetallselektiver extraktionsmittel und ihre anwendbarkeit in der analytischen chemie

Summary The classical fire assay technique is still the most important procedure for the isolation and determination of precious metals. However, the lead collection system is basically suitable for extracting gold and silver, less for platinum, palladium and the rare precious metals. Extensive corrections are required to achieve accurate results. Many attempts are published to improve the situation by applying alternate collectors, additional chemical separations and instrumental determinative methods, such as atomic absorption and plasma emission spectrometry.Promising methods could be employed if certain separating media (solvent extractants, ion-exchange resins) are provided which extract precious metals selectively and reversibly. In such a case the final calibration step can be carried out with standard solutions of definite composition.The designing of ler made extractants has to consider the complex nature of the solution chemistry of precious metals. Hence, the relationship between metal properties and solvent extraction and ion exchange is briefly surveyed. The outlook with respect to the authors' research activities is focussed on the synthesis, characterization and application of new organic liquid and solid extractants (modified polystyrene and silica gel). These materials are based on chelating formazans and ion-exchanging tetrazolium salts. The selectivity, efficiency and mechanism of metal extraction and re-extraction are reviewed with respect to the effects of substituents attached to the metal binding groups, the influence of organic solvents and the nature of various supports (silica gel, polystyrene). Certain analytical applications are presented, e.g. the determination of silver, gold, platinum and palladium by means of formazan extraction, sorption on to tetrazolium-resins and DCP-emission spectrometry. The methods offer the advantages of selectivity and simplicity.

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Herrn Prof. Dr. G. Tölg zum 60. Geburtstag gewidmet